Provided by: peewee_3.7.0+dfsg-2build2_all 
NAME
peewee - peewee Documentation [image]
Peewee is a simple and small ORM. It has few (but expressive) concepts, making it easy to learn and
intuitive to use.
• a small, expressive ORM
• python 2.7+ and 3.4+ (developed with 3.6)
• supports sqlite, mysql and postgresql
• tons of extensions
postgresqlmysqlsqlite
Peewee's source code hosted on GitHub.
New to peewee? These may help:
• Quickstart
• Example twitter app
• Models and fields
• Querying
• Relationships and joins
CONTENTS:
Installing and Testing
Most users will want to simply install the latest version, hosted on PyPI:
pip install peewee
Peewee comes with a couple C extensions that will be built if Cython is available.
• Speedups, which includes miscellaneous functions re-implemented with Cython.
• Sqlite extensions, which includes Cython implementations of the SQLite date manipulation functions, the
REGEXP operator, and full-text search result ranking algorithms.
Installing with git
The project is hosted at https://github.com/coleifer/peewee and can be installed using git:
git clone https://github.com/coleifer/peewee.git
cd peewee
python setup.py install
NOTE:
On some systems you may need to use sudo python setup.py install to install peewee system-wide.
If you would like to build the SQLite extension in a git checkout, you can run:
# Build the C extension and place shared libraries alongside other modules.
python setup.py build_ext -i
Running tests
You can test your installation by running the test suite.
python runtests.py
You can test specific features or specific database drivers using the runtests.py script. To view the
available test runner options, use:
python runtests.py --help
NOTE:
To run tests against Postgres or MySQL you need to create a database named "peewee_test". To test the
Postgres extension module, you will also want to install the HStore extension in the postgres test
database:
-- install the hstore extension on the peewee_test postgres db.
CREATE EXTENSION hstore;
Optional dependencies
NOTE:
To use Peewee, you typically won't need anything outside the standard library, since most Python
distributions are compiled with SQLite support. You can test by running import sqlite3 in the Python
console. If you wish to use another database, there are many DB-API 2.0-compatible drivers out there,
such as pymysql or psycopg2 for MySQL and Postgres respectively.
• Cython: used for various speedups. Can give a big boost to certain operations, particularly if you use
SQLite. Since the generated C files are included with the package distribution, Cython is no longer
required to use the C extensions (as of v3.6.0).
• apsw: an optional 3rd-party SQLite binding offering greater performance and comprehensive support for
SQLite's C APIs. Use with APSWDatabase.
• gevent is an optional dependency for SqliteQueueDatabase (though it works with threading just fine).
• BerkeleyDB can be compiled with a SQLite frontend, which works with Peewee. Compiling can be tricky so
here are instructions.
• Lastly, if you use the Flask framework, there are helper extension modules available.
Note on the SQLite extensions
Peewee includes two SQLite-specific C extensions which provide additional functionality and improved
performance for SQLite database users. Peewee will attempt to determine ahead-of-time if SQLite3 is
installed, and only build the SQLite extensions if the SQLite shared-library is available on your system.
If, however, you receive errors like the following when attempting to install Peewee, you can explicitly
disable the compilation of the SQLite C extensions by settings the NO_SQLITE environment variable.
Here is how to install Peewee with the SQLite extensions explicitly disabled:
$ NO_SQLITE=1 python setup.py install
Quickstart
This document presents a brief, high-level overview of Peewee's primary features. This guide will cover:
• Model Definition
• Storing data
• Retrieving Data
NOTE:
If you'd like something a bit more meaty, there is a thorough tutorial on creating a "twitter"-style
web app using peewee and the Flask framework. In the projects examples/ folder you can find more
self-contained Peewee examples, like a blog app.
I strongly recommend opening an interactive shell session and running the code. That way you can get a
feel for typing in queries.
Model Definition
Model classes, fields and model instances all map to database concepts:
┌───────────────┬─────────────────────────┐
│Object │ Corresponds to... │
├───────────────┼─────────────────────────┤
│Model class │ Database table │
├───────────────┼─────────────────────────┤
│Field instance │ Column on a table │
├───────────────┼─────────────────────────┤
│Model instance │ Row in a database table │
└───────────────┴─────────────────────────┘
When starting a project with peewee, it's typically best to begin with your data model, by defining one
or more Model classes:
from peewee import *
db = SqliteDatabase('people.db')
class Person(Model):
name = CharField()
birthday = DateField()
class Meta:
database = db # This model uses the "people.db" database.
NOTE:
Note that we named our model Person instead of People. This is a convention you should follow -- even
though the table will contain multiple people, we always name the class using the singular form.
There are lots of field types suitable for storing various types of data. Peewee handles converting
between pythonic values those used by the database, so you can use Python types in your code without
having to worry.
Things get interesting when we set up relationships between models using foreign key relationships. This
is simple with peewee:
class Pet(Model):
owner = ForeignKeyField(Person, backref='pets')
name = CharField()
animal_type = CharField()
class Meta:
database = db # this model uses the "people.db" database
Now that we have our models, let's connect to the database. Although it's not necessary to open the
connection explicitly, it is good practice since it will reveal any errors with your database connection
immediately, as opposed to some arbitrary time later when the first query is executed. It is also good to
close the connection when you are done -- for instance, a web app might open a connection when it
receives a request, and close the connection when it sends the response.
db.connect()
We'll begin by creating the tables in the database that will store our data. This will create the tables
with the appropriate columns, indexes, sequences, and foreign key constraints:
db.create_tables([Person, Pet])
Storing data
Let's begin by populating the database with some people. We will use the save() and create() methods to
add and update people's records.
from datetime import date
uncle_bob = Person(name='Bob', birthday=date(1960, 1, 15))
uncle_bob.save() # bob is now stored in the database
# Returns: 1
NOTE:
When you call save(), the number of rows modified is returned.
You can also add a person by calling the create() method, which returns a model instance:
grandma = Person.create(name='Grandma', birthday=date(1935, 3, 1))
herb = Person.create(name='Herb', birthday=date(1950, 5, 5))
To update a row, modify the model instance and call save() to persist the changes. Here we will change
Grandma's name and then save the changes in the database:
grandma.name = 'Grandma L.'
grandma.save() # Update grandma's name in the database.
# Returns: 1
Now we have stored 3 people in the database. Let's give them some pets. Grandma doesn't like animals in
the house, so she won't have any, but Herb is an animal lover:
bob_kitty = Pet.create(owner=uncle_bob, name='Kitty', animal_type='cat')
herb_fido = Pet.create(owner=herb, name='Fido', animal_type='dog')
herb_mittens = Pet.create(owner=herb, name='Mittens', animal_type='cat')
herb_mittens_jr = Pet.create(owner=herb, name='Mittens Jr', animal_type='cat')
After a long full life, Mittens sickens and dies. We need to remove him from the database:
herb_mittens.delete_instance() # he had a great life
# Returns: 1
NOTE:
The return value of delete_instance() is the number of rows removed from the database.
Uncle Bob decides that too many animals have been dying at Herb's house, so he adopts Fido:
herb_fido.owner = uncle_bob
herb_fido.save()
Retrieving Data
The real strength of our database is in how it allows us to retrieve data through queries. Relational
databases are excellent for making ad-hoc queries.
Getting single records
Let's retrieve Grandma's record from the database. To get a single record from the database, use
Select.get():
grandma = Person.select().where(Person.name == 'Grandma L.').get()
We can also use the equivalent shorthand Model.get():
grandma = Person.get(Person.name == 'Grandma L.')
Lists of records
Let's list all the people in the database:
for person in Person.select():
print(person.name)
# prints:
# Bob
# Grandma L.
# Herb
Let's list all the cats and their owner's name:
query = Pet.select().where(Pet.animal_type == 'cat')
for pet in query:
print(pet.name, pet.owner.name)
# prints:
# Kitty Bob
# Mittens Jr Herb
ATTENTION:
There is a big problem with the previous query: because we are accessing pet.owner.name and we did not
select this relation in our original query, peewee will have to perform an additional query to
retrieve the pet's owner. This behavior is referred to as N+1 and it should generally be avoided.
For an in-depth guide to working with relationships and joins, refer to the relationships
documentation.
We can avoid the extra queries by selecting both Pet and Person, and adding a join.
query = (Pet
.select(Pet, Person)
.join(Person)
.where(Pet.animal_type == 'cat'))
for pet in query:
print(pet.name, pet.owner.name)
# prints:
# Kitty Bob
# Mittens Jr Herb
Let's get all the pets owned by Bob:
for pet in Pet.select().join(Person).where(Person.name == 'Bob'):
print(pet.name)
# prints:
# Kitty
# Fido
We can do another cool thing here to get bob's pets. Since we already have an object to represent Bob, we
can do this instead:
for pet in Pet.select().where(Pet.owner == uncle_bob):
print(pet.name)
Sorting
Let's make sure these are sorted alphabetically by adding an order_by() clause:
for pet in Pet.select().where(Pet.owner == uncle_bob).order_by(Pet.name):
print(pet.name)
# prints:
# Fido
# Kitty
Let's list all the people now, youngest to oldest:
for person in Person.select().order_by(Person.birthday.desc()):
print(person.name, person.birthday)
# prints:
# Bob 1960-01-15
# Herb 1950-05-05
# Grandma L. 1935-03-01
Combining filter expressions
Peewee supports arbitrarily-nested expressions. Let's get all the people whose birthday was either:
• before 1940 (grandma)
• after 1959 (bob)
d1940 = date(1940, 1, 1)
d1960 = date(1960, 1, 1)
query = (Person
.select()
.where((Person.birthday < d1940) | (Person.birthday > d1960)))
for person in query:
print(person.name, person.birthday)
# prints:
# Bob 1960-01-15
# Grandma L. 1935-03-01
Now let's do the opposite. People whose birthday is between 1940 and 1960:
query = (Person
.select()
.where(Person.birthday.between(d1940, d1960)))
for person in query:
print(person.name, person.birthday)
# prints:
# Herb 1950-05-05
Aggregates and Prefetch
Now let's list all the people and how many pets they have:
for person in Person.select():
print(person.name, person.pets.count(), 'pets')
# prints:
# Bob 2 pets
# Grandma L. 0 pets
# Herb 1 pets
Once again we've run into a classic example of N+1 query behavior. In this case, we're executing an
additional query for every Person returned by the original SELECT! We can avoid this by performing a JOIN
and using a SQL function to aggregate the results.
query = (Person
.select(Person, fn.COUNT(Pet.id).alias('pet_count'))
.join(Pet, JOIN.LEFT_OUTER) # include people without pets.
.group_by(Person)
.order_by(Person.name))
for person in query:
# "pet_count" becomes an attribute on the returned model instances.
print(person.name, person.pet_count, 'pets')
# prints:
# Bob 2 pets
# Grandma L. 0 pets
# Herb 1 pets
Now let's list all the people and the names of all their pets. As you may have guessed, this could easily
turn into another N+1 situation if we're not careful.
Before diving into the code, consider how this example is different from the earlier example where we
listed all the pets and their owner's name. A pet can only have one owner, so when we performed the join
from Pet to Person, there was always going to be a single match. The situation is different when we are
joining from Person to Pet because a person may have zero pets or they may have several pets. Because
we're using a relational databases, if we were to do a join from Person to Pet then every person with
multiple pets would be repeated, once for each pet.
It would look like this:
query = (Person
.select(Person, Pet)
.join(Pet, JOIN.LEFT_OUTER)
.order_by(Person.name, Pet.name))
for person in query:
# We need to check if they have a pet instance attached, since not all
# people have pets.
if hasattr(person, 'pet'):
print(person.name, person.pet.name)
else:
print(person.name, 'no pets')
# prints:
# Bob Fido
# Bob Kitty
# Grandma L. no pets
# Herb Mittens Jr
Usually this type of duplication is undesirable. To accommodate the more common (and intuitive) workflow
of listing a person and attaching a list of that person's pets, we can use a special method called
prefetch():
query = Person.select().order_by(Person.name).prefetch(Pet)
for person in query:
print(person.name)
for pet in person.pets:
print(' *', pet.name)
# prints:
# Bob
# * Kitty
# * Fido
# Grandma L.
# Herb
# * Mittens Jr
SQL Functions
One last query. This will use a SQL function to find all people whose names start with either an upper or
lower-case G:
expression = fn.Lower(fn.Substr(Person.name, 1, 1)) == 'g'
for person in Person.select().where(expression):
print(person.name)
# prints:
# Grandma L.
Closing the database
We're done with our database, let's close the connection:
db.close()
This is just the basics! You can make your queries as complex as you like. Check the documentation on
querying for more info.
Working with existing databases
If you already have a database, you can autogenerate peewee models using pwiz. For instance, if I have a
postgresql database named charles_blog, I might run:
python -m pwiz -e postgresql charles_blog > blog_models.py
What next?
That's it for the quickstart. If you want to look at a full web-app, check out the example-app.
Example app
We'll be building a simple twitter-like site. The source code for the example can be found in the
examples/twitter directory. You can also browse the source-code on github. There is also an example blog
app if that's more to your liking, however it is not covered in this guide.
The example app uses the flask web framework which is very easy to get started with. If you don't have
flask already, you will need to install it to run the example:
pip install flask
Running the example
[image]
After ensuring that flask is installed, cd into the twitter example directory and execute the
run_example.py script:
python run_example.py
The example app will be accessible at http://localhost:5000/
Diving into the code
For simplicity all example code is contained within a single module, examples/twitter/app.py. For a guide
on structuring larger Flask apps with peewee, check out Structuring Flask Apps.
Models
In the spirit of the popular web framework Django, peewee uses declarative model definitions. If you're
not familiar with Django, the idea is that you declare a model class for each table. The model class then
defines one or more field attributes which correspond to the table's columns. For the twitter clone,
there are just three models:
User: Represents a user account and stores the username and password, an email address for generating
avatars using gravatar, and a datetime field indicating when that account was created.
Relationship:
This is a utility model that contains two foreign-keys to the User model and stores which users
follow one another.
Message:
Analogous to a tweet. The Message model stores the text content of the tweet, when it was created,
and who posted it (foreign key to User).
If you like UML, these are the tables and relationships: [image]
In order to create these models we need to instantiate a SqliteDatabase object. Then we define our model
classes, specifying the columns as Field instances on the class.
# create a peewee database instance -- our models will use this database to
# persist information
database = SqliteDatabase(DATABASE)
# model definitions -- the standard "pattern" is to define a base model class
# that specifies which database to use. then, any subclasses will automatically
# use the correct storage.
class BaseModel(Model):
class Meta:
database = database
# the user model specifies its fields (or columns) declaratively, like django
class User(BaseModel):
username = CharField(unique=True)
password = CharField()
email = CharField()
join_date = DateTimeField()
# this model contains two foreign keys to user -- it essentially allows us to
# model a "many-to-many" relationship between users. by querying and joining
# on different columns we can expose who a user is "related to" and who is
# "related to" a given user
class Relationship(BaseModel):
from_user = ForeignKeyField(User, backref='relationships')
to_user = ForeignKeyField(User, backref='related_to')
class Meta:
# `indexes` is a tuple of 2-tuples, where the 2-tuples are
# a tuple of column names to index and a boolean indicating
# whether the index is unique or not.
indexes = (
# Specify a unique multi-column index on from/to-user.
(('from_user', 'to_user'), True),
)
# a dead simple one-to-many relationship: one user has 0..n messages, exposed by
# the foreign key. because we didn't specify, a users messages will be accessible
# as a special attribute, User.messages
class Message(BaseModel):
user = ForeignKeyField(User, backref='messages')
content = TextField()
pub_date = DateTimeField()
NOTE:
Note that we create a BaseModel class that simply defines what database we would like to use. All
other models then extend this class and will also use the correct database connection.
Peewee supports many different field types which map to different column types commonly supported by
database engines. Conversion between python types and those used in the database is handled
transparently, allowing you to use the following in your application:
• Strings (unicode or otherwise)
• Integers, floats, and Decimal numbers.
• Boolean values
• Dates, times and datetimes
• None (NULL)
• Binary data
Creating tables
In order to start using the models, its necessary to create the tables. This is a one-time operation and
can be done quickly using the interactive interpreter. We can create a small helper function to
accomplish this:
def create_tables():
with database:
database.create_tables([User, Relationship, Message])
Open a python shell in the directory alongside the example app and execute the following:
>>> from app import *
>>> create_tables()
NOTE:
If you encounter an ImportError it means that either flask or peewee was not found and may not be
installed correctly. Check the installation document for instructions on installing peewee.
Every model has a create_table() classmethod which runs a SQL CREATE TABLE statement in the database.
This method will create the table, including all columns, foreign-key constraints, indexes, and
sequences. Usually this is something you'll only do once, whenever a new model is added.
Peewee provides a helper method Database.create_tables() which will resolve inter-model dependencies and
call create_table() on each model, ensuring the tables are created in order.
NOTE:
Adding fields after the table has been created will required you to either drop the table and
re-create it or manually add the columns using an ALTER TABLE query.
Alternatively, you can use the schema migrations extension to alter your database schema using Python.
Establishing a database connection
You may have noticed in the above model code that there is a class defined on the base model named Meta
that sets the database attribute. Peewee allows every model to specify which database it uses. There are
many Meta options you can specify which control the behavior of your model.
This is a peewee idiom:
DATABASE = 'tweepee.db'
# Create a database instance that will manage the connection and
# execute queries
database = SqliteDatabase(DATABASE)
# Create a base-class all our models will inherit, which defines
# the database we'll be using.
class BaseModel(Model):
class Meta:
database = database
When developing a web application, it's common to open a connection when a request starts, and close it
when the response is returned. You should always manage your connections explicitly. For instance, if you
are using a connection pool, connections will only be recycled correctly if you call connect() and
close().
We will tell flask that during the request/response cycle we need to create a connection to the database.
Flask provides some handy decorators to make this a snap:
@app.before_request
def before_request():
database.connect()
@app.after_request
def after_request(response):
database.close()
return response
NOTE:
Peewee uses thread local storage to manage connection state, so this pattern can be used with
multi-threaded WSGI servers.
Making queries
In the User model there are a few instance methods that encapsulate some user-specific functionality:
• following(): who is this user following?
• followers(): who is following this user?
These methods are similar in their implementation but with an important difference in the SQL JOIN and
WHERE clauses:
def following(self):
# query other users through the "relationship" table
return (User
.select()
.join(Relationship, on=Relationship.to_user)
.where(Relationship.from_user == self)
.order_by(User.username))
def followers(self):
return (User
.select()
.join(Relationship, on=Relationship.from_user)
.where(Relationship.to_user == self)
.order_by(User.username))
Creating new objects
When a new user wants to join the site we need to make sure the username is available, and if so, create
a new User record. Looking at the join() view, we can see that our application attempts to create the
User using Model.create(). We defined the User.username field with a unique constraint, so if the
username is taken the database will raise an IntegrityError.
try:
with database.atomic():
# Attempt to create the user. If the username is taken, due to the
# unique constraint, the database will raise an IntegrityError.
user = User.create(
username=request.form['username'],
password=md5(request.form['password']).hexdigest(),
email=request.form['email'],
join_date=datetime.datetime.now())
# mark the user as being 'authenticated' by setting the session vars
auth_user(user)
return redirect(url_for('homepage'))
except IntegrityError:
flash('That username is already taken')
We will use a similar approach when a user wishes to follow someone. To indicate a following
relationship, we create a row in the Relationship table pointing from one user to another. Due to the
unique index on from_user and to_user, we will be sure not to end up with duplicate rows:
user = get_object_or_404(User, username=username)
try:
with database.atomic():
Relationship.create(
from_user=get_current_user(),
to_user=user)
except IntegrityError:
pass
Performing subqueries
If you are logged-in and visit the twitter homepage, you will see tweets from the users that you follow.
In order to implement this cleanly, we can use a subquery:
NOTE:
The subquery, user.following(), by default would ordinarily select all the columns on the User model.
Because we're using it as a subquery, peewee will only select the primary key.
# python code
user = get_current_user()
messages = (Message
.select()
.where(Message.user.in_(user.following()))
.order_by(Message.pub_date.desc()))
This code corresponds to the following SQL query:
SELECT t1."id", t1."user_id", t1."content", t1."pub_date"
FROM "message" AS t1
WHERE t1."user_id" IN (
SELECT t2."id"
FROM "user" AS t2
INNER JOIN "relationship" AS t3
ON t2."id" = t3."to_user_id"
WHERE t3."from_user_id" = ?
)
Other topics of interest
There are a couple other neat things going on in the example app that are worth mentioning briefly.
• Support for paginating lists of results is implemented in a simple function called object_list (after
it's corollary in Django). This function is used by all the views that return lists of objects.
def object_list(template_name, qr, var_name='object_list', **kwargs):
kwargs.update(
page=int(request.args.get('page', 1)),
pages=qr.count() / 20 + 1)
kwargs[var_name] = qr.paginate(kwargs['page'])
return render_template(template_name, **kwargs)
• Simple authentication system with a login_required decorator. The first function simply adds user data
into the current session when a user successfully logs in. The decorator login_required can be used to
wrap view functions, checking for whether the session is authenticated and if not redirecting to the
login page.
def auth_user(user):
session['logged_in'] = True
session['user'] = user
session['username'] = user.username
flash('You are logged in as %s' % (user.username))
def login_required(f):
@wraps(f)
def inner(*args, **kwargs):
if not session.get('logged_in'):
return redirect(url_for('login'))
return f(*args, **kwargs)
return inner
• Return a 404 response instead of throwing exceptions when an object is not found in the database.
def get_object_or_404(model, *expressions):
try:
return model.get(*expressions)
except model.DoesNotExist:
abort(404)
NOTE:
To avoid having to frequently copy/paste object_list() or get_object_or_404(), these functions are
included as part of the playhouse flask extension module.
from playhouse.flask_utils import get_object_or_404, object_list
More examples
There are more examples included in the peewee examples directory, including:
• Example blog app using Flask and peewee. Also see accompanying blog post.
• An encrypted command-line diary. There is a companion blog post you might enjoy as well.
• Analytics web-service (like a lite version of Google Analytics). Also check out the companion blog
post.
NOTE:
Like these snippets and interested in more? Check out flask-peewee - a flask plugin that provides a
django-like Admin interface, RESTful API, Authentication and more for your peewee models.
Contributing
In order to continually improve, Peewee needs the help of developers like you. Whether it's contributing
patches, submitting bug reports, or just asking and answering questions, you are helping to make Peewee a
better library.
In this document I'll describe some of the ways you can help.
Patches
Do you have an idea for a new feature, or is there a clunky API you'd like to improve? Before coding it
up and submitting a pull-request, open a new issue on GitHub describing your proposed changes. This
doesn't have to be anything formal, just a description of what you'd like to do and why.
When you're ready, you can submit a pull-request with your changes. Successful patches will have the
following:
• Unit tests.
• Documentation, both prose form and general API documentation.
• Code that conforms stylistically with the rest of the Peewee codebase.
Bugs
If you've found a bug, please check to see if it has already been reported, and if not create an issue on
GitHub. The more information you include, the more quickly the bug will get fixed, so please try to
include the following:
• Traceback and the error message (please format your code!)
• Relevant portions of your code or code to reproduce the error
• Peewee version: python -c "from peewee import __version__; print(__version__)"
• Which database you're using
If you have found a bug in the code and submit a failing test-case, then hats-off to you, you are a hero!
Questions
If you have questions about how to do something with peewee, then I recommend either:
• Ask on StackOverflow. I check SO just about every day for new peewee questions and try to answer them.
This has the benefit also of preserving the question and answer for other people to find.
• Ask on the mailing list, https://groups.google.com/group/peewee-orm
Database
The Peewee Database object represents a connection to a database. The Database class is instantiated
with all the information needed to open a connection to a database, and then can be used to:
• Open and close connections.
• Execute queries.
• Manage transactions (and savepoints).
• Introspect tables, columns, indexes, and constraints.
Peewee comes with support for SQLite, MySQL and Postgres. Each database class provides some basic,
database-specific configuration options.
from peewee import *
# SQLite database using WAL journal mode and 64MB cache.
sqlite_db = SqliteDatabase('/path/to/app.db', pragmas={
'journal_mode': 'wal',
'cache_size': -1024 * 64})
# Connect to a MySQL database on network.
mysql_db = MySQLDatabase('my_app', user='app', password='db_password',
host='10.1.0.8', port=3316)
# Connect to a Postgres database.
pg_db = PostgresqlDatabase('my_app', user='postgres', password='secret',
host='10.1.0.9', port=5432)
Peewee provides advanced support for SQLite and Postgres via database-specific extension modules. To use
the extended-functionality, import the appropriate database-specific module and use the database class
provided:
from playhouse.sqlite_ext import SqliteExtDatabase
# Use SQLite (will register a REGEXP function and set busy timeout to 3s).
db = SqliteExtDatabase('/path/to/app.db', regexp_function=True, timeout=3,
pragmas={'journal_mode': 'wal'})
from playhouse.postgres_ext import PostgresqlExtDatabase
# Use Postgres (and register hstore extension).
db = PostgresqlExtDatabase('my_app', user='postgres', register_hstore=True)
For more information on database extensions, see:
• postgres_ext
• sqlite_ext
• sqlcipher_ext
• apsw
• sqliteq
Initializing a Database
The Database initialization method expects the name of the database as the first parameter. Subsequent
keyword arguments are passed to the underlying database driver when establishing the connection, allowing
you to pass vendor-specific parameters easily.
For instance, with Postgresql it is common to need to specify the host, user and password when creating
your connection. These are not standard Peewee Database parameters, so they will be passed directly back
to psycopg2 when creating connections:
db = PostgresqlDatabase(
'database_name', # Required by Peewee.
user='postgres', # Will be passed directly to psycopg2.
password='secret', # Ditto.
host='db.mysite.com') # Ditto.
As another example, the pymysql driver accepts a charset parameter which is not a standard Peewee
Database parameter. To set this value, simply pass in charset alongside your other values:
db = MySQLDatabase('database_name', user='www-data', charset='utf8mb4')
Consult your database driver's documentation for the available parameters:
• Postgres: psycopg2
• MySQL: MySQLdb
• MySQL: pymysql
• SQLite: sqlite3
Using Postgresql
To connect to a Postgresql database, we will use PostgresqlDatabase. The first parameter is always the
name of the database, and after that you can specify arbitrary psycopg2 parameters.
psql_db = PostgresqlDatabase('my_database', user='postgres')
class BaseModel(Model):
"""A base model that will use our Postgresql database"""
class Meta:
database = psql_db
class User(BaseModel):
username = CharField()
The playhouse contains a Postgresql extension module which provides many postgres-specific features such
as:
• Arrays
• HStore
• JSON
• Server-side cursors
• And more!
If you would like to use these awesome features, use the PostgresqlExtDatabase from the
playhouse.postgres_ext module:
from playhouse.postgres_ext import PostgresqlExtDatabase
psql_db = PostgresqlExtDatabase('my_database', user='postgres')
Using SQLite
To connect to a SQLite database, we will use SqliteDatabase. The first parameter is the filename
containing the database, or the string ':memory:' to create an in-memory database. After the database
filename, you can specify a list or pragmas or any other arbitrary sqlite3 parameters.
sqlite_db = SqliteDatabase('my_app.db', pragmas={'journal_mode': 'wal'})
class BaseModel(Model):
"""A base model that will use our Sqlite database."""
class Meta:
database = sqlite_db
class User(BaseModel):
username = TextField()
# etc, etc
Peewee includes a SQLite extension module which provides many SQLite-specific features such as full-text
search, json extension support, and much, much more. If you would like to use these awesome features, use
the SqliteExtDatabase from the playhouse.sqlite_ext module:
from playhouse.sqlite_ext import SqliteExtDatabase
sqlite_db = SqliteExtDatabase('my_app.db', pragmas={
'journal_mode': 'wal', # WAL-mode.
'cache_size': -64 * 1000, # 64MB cache.
'synchronous': 0}) # Let the OS manage syncing.
PRAGMA statements
SQLite allows run-time configuration of a number of parameters through PRAGMA statements (SQLite
documentation). These statements are typically run when a new database connection is created. To run
one or more PRAGMA statements against new connections, you can specify them as a dictionary or a list of
2-tuples containing the pragma name and value:
db = SqliteDatabase('my_app.db', pragmas={
'journal_mode': 'wal',
'cache_size': 10000, # 10000 pages, or ~40MB
'foreign_keys': 1, # Enforce foreign-key constraints
})
PRAGMAs may also be configured dynamically using either the pragma() method or the special properties
exposed on the SqliteDatabase object:
# Set cache size to 64MB for *current connection*.
db.pragma('cache_size', -1024 * 64)
# Same as above.
db.cache_size = -1024 * 64
# Read the value of several pragmas:
print('cache_size:', db.cache_size)
print('foreign_keys:', db.foreign_keys)
print('journal_mode:', db.journal_mode)
print('page_size:', db.page_size)
# Set foreign_keys pragma on current connection *AND* on all
# connections opened subsequently.
db.pragma('foreign_keys', 1, permanent=True)
ATTENTION:
Pragmas set using the pragma() method, by default, do not persist after the connection is closed. To
configure a pragma to be run whenever a connection is opened, specify permanent=True.
NOTE:
A full list of PRAGMA settings, their meaning and accepted values can be found in the SQLite
documentation: http://sqlite.org/pragma.html
Recommended Settings
The following settings are what I use with SQLite for a typical web application database.
┌─────────────────────────┬─────────────────────┬──────────────────────────────┐
│pragma │ recommended setting │ explanation │
├─────────────────────────┼─────────────────────┼──────────────────────────────┤
│journal_mode │ wal │ allow readers and writers to │
│ │ │ co-exist │
├─────────────────────────┼─────────────────────┼──────────────────────────────┤
│cache_size │ -1 * data_size_kb │ set page-cache size in KiB, │
│ │ │ e.g. -32000 = 32MB │
├─────────────────────────┼─────────────────────┼──────────────────────────────┤
│foreign_keys │ 1 │ enforce foreign-key │
│ │ │ constraints │
├─────────────────────────┼─────────────────────┼──────────────────────────────┤
│ignore_check_constraints │ 0 │ enforce CHECK constraints │
├─────────────────────────┼─────────────────────┼──────────────────────────────┤
│synchronous │ 0 │ let OS handle fsync (use │
│ │ │ with caution) │
└─────────────────────────┴─────────────────────┴──────────────────────────────┘
Example database using the above options:
db = SqliteDatabase('my_app.db', pragmas={
'journal_mode': 'wal',
'cache_size': -1 * 64000, # 64MB
'foreign_keys': 1,
'ignore_check_constraints': 0,
'synchronous': 0})
User-defined functions
SQLite can be extended with user-defined Python code. The SqliteDatabase class supports three types of
user-defined extensions:
• Functions - which take any number of parameters and return a single value.
• Aggregates - which aggregate parameters from multiple rows and return a single value.
• Collations - which describe how to sort some value.
NOTE:
For even more extension support, see SqliteExtDatabase, which is in the playhouse.sqlite_ext module.
Example user-defined function:
db = SqliteDatabase('analytics.db')
from urllib.parse import urlparse
@db.func('hostname')
def hostname(url):
if url is not None:
return urlparse(url).netloc
# Call this function in our code:
# The following finds the most common hostnames of referrers by count:
query = (PageView
.select(fn.hostname(PageView.referrer), fn.COUNT(PageView.id))
.group_by(fn.hostname(PageView.referrer))
.order_by(fn.COUNT(PageView.id).desc()))
Example user-defined aggregate:
from hashlib import md5
@db.aggregate('md5')
class MD5Checksum(object):
def __init__(self):
self.checksum = md5()
def step(self, value):
self.checksum.update(value.encode('utf-8'))
def finalize(self):
return self.checksum.hexdigest()
# Usage:
# The following computes an aggregate MD5 checksum for files broken
# up into chunks and stored in the database.
query = (FileChunk
.select(FileChunk.filename, fn.MD5(FileChunk.data))
.group_by(FileChunk.filename)
.order_by(FileChunk.filename, FileChunk.sequence))
Example collation:
@db.collation('ireverse')
def collate_reverse(s1, s2):
# Case-insensitive reverse.
s1, s2 = s1.lower(), s2.lower()
return (s1 < s2) - (s1 > s2) # Equivalent to -cmp(s1, s2)
# To use this collation to sort books in reverse order...
Book.select().order_by(collate_reverse.collation(Book.title))
# Or...
Book.select().order_by(Book.title.asc(collation='reverse'))
Example user-defined table-value function (see TableFunction and table_function) for additional details:
from playhouse.sqlite_ext import TableFunction
db = SqliteDatabase('my_app.db')
@db.table_function('series')
class Series(TableFunction):
columns = ['value']
params = ['start', 'stop', 'step']
def initialize(self, start=0, stop=None, step=1):
"""
Table-functions declare an initialize() method, which is
called with whatever arguments the user has called the
function with.
"""
self.start = self.current = start
self.stop = stop or float('Inf')
self.step = step
def iterate(self, idx):
"""
Iterate is called repeatedly by the SQLite database engine
until the required number of rows has been read **or** the
function raises a `StopIteration` signalling no more rows
are available.
"""
if self.current > self.stop:
raise StopIteration
ret, self.current = self.current, self.current + self.step
return (ret,)
# Usage:
cursor = db.execute_sql('SELECT * FROM series(?, ?, ?)', (0, 5, 2))
for value, in cursor:
print(value)
# Prints:
# 0
# 2
# 4
For more information, see:
• SqliteDatabase.func()
• SqliteDatabase.aggregate()
• SqliteDatabase.collation()
• SqliteDatabase.table_function()
• For even more SQLite extensions, see sqlite_ext
Set locking mode for transaction
SQLite transactions can be opened in three different modes:
• Deferred (default) - only acquires lock when a read or write is performed. The first read creates a
shared lock and the first write creates a reserved lock. Because the acquisition of the lock is
deferred until actually needed, it is possible that another thread or process could create a separate
transaction and write to the database after the BEGIN on the current thread has executed.
• Immediate - a reserved lock is acquired immediately. In this mode, no other database may write to the
database or open an immediate or exclusive transaction. Other processes can continue to read from the
database, however.
• Exclusive - opens an exclusive lock which prevents all (except for read uncommitted) connections from
accessing the database until the transaction is complete.
Example specifying the locking mode:
db = SqliteDatabase('app.db')
with db.atomic('EXCLUSIVE'):
do_something()
@db.atomic('IMMEDIATE')
def some_other_function():
# This function is wrapped in an "IMMEDIATE" transaction.
do_something_else()
For more information, see the SQLite locking documentation. To learn more about transactions in Peewee,
see the Managing Transactions documentation.
APSW, an Advanced SQLite Driver
Peewee also comes with an alternate SQLite database that uses apsw, an advanced Python SQLite driver.
More information on APSW can be obtained on the APSW project website. APSW provides special features
like:
• Virtual tables, virtual file-systems, Blob I/O, backups and file control.
• Connections can be shared across threads without any additional locking.
• Transactions are managed explicitly by your code.
• Unicode is handled correctly.
• APSW is faster that the standard library sqlite3 module.
• Exposes pretty much the entire SQLite C API to your Python app.
If you would like to use APSW, use the APSWDatabase from the apsw_ext module:
from playhouse.apsw_ext import APSWDatabase
apsw_db = APSWDatabase('my_app.db')
Using MySQL
To connect to a MySQL database, we will use MySQLDatabase. After the database name, you can specify
arbitrary connection parameters that will be passed back to the driver (either MySQLdb or pymysql).
mysql_db = MySQLDatabase('my_database')
class BaseModel(Model):
"""A base model that will use our MySQL database"""
class Meta:
database = mysql_db
class User(BaseModel):
username = CharField()
# etc, etc
Error 2006: MySQL server has gone away
This particular error can occur when MySQL kills an idle database connection. This typically happens
with web apps that do not explicitly manage database connections. What happens is your application
starts, a connection is opened to handle the first query that executes, and, since that connection is
never closed, it remains open, waiting for more queries.
To fix this, make sure you are explicitly connecting to the database when you need to execute queries,
and close your connection when you are done. In a web-application, this typically means you will open a
connection when a request comes in, and close the connection when you return a response.
See the Framework Integration section for examples of configuring common web frameworks to manage
database connections.
Connecting using a Database URL
The playhouse module db_url provides a helper connect() function that accepts a database URL and returns
a Database instance.
Example code:
import os
from peewee import *
from playhouse.db_url import connect
# Connect to the database URL defined in the environment, falling
# back to a local Sqlite database if no database URL is specified.
db = connect(os.environ.get('DATABASE') or 'sqlite:///default.db')
class BaseModel(Model):
class Meta:
database = db
Example database URLs:
• sqlite:///my_database.db will create a SqliteDatabase instance for the file my_database.db in the
current directory.
• sqlite:///:memory: will create an in-memory SqliteDatabase instance.
• postgresql://postgres:my_password@localhost:5432/my_database will create a PostgresqlDatabase instance.
A username and password are provided, as well as the host and port to connect to.
• mysql://user:passwd@ip:port/my_db will create a MySQLDatabase instance for the local MySQL database
my_db.
• More examples in the db_url documentation.
Run-time database configuration
Sometimes the database connection settings are not known until run-time, when these values may be loaded
from a configuration file or the environment. In these cases, you can defer the initialization of the
database by specifying None as the database_name.
database = PostgresqlDatabase(None) # Un-initialized database.
class SomeModel(Model):
class Meta:
database = database
If you try to connect or issue any queries while your database is uninitialized you will get an
exception:
>>> database.connect()
Exception: Error, database not properly initialized before opening connection
To initialize your database, call the init() method with the database name and any additional keyword
arguments:
database_name = raw_input('What is the name of the db? ')
database.init(database_name, host='localhost', user='postgres')
For even more control over initializing your database, see the next section, Dynamically defining a
database.
Dynamically defining a database
For even more control over how your database is defined/initialized, you can use the Proxy helper. Proxy
objects act as a placeholder, and then at run-time you can swap it out for a different object. In the
example below, we will swap out the database depending on how the app is configured:
database_proxy = Proxy() # Create a proxy for our db.
class BaseModel(Model):
class Meta:
database = database_proxy # Use proxy for our DB.
class User(BaseModel):
username = CharField()
# Based on configuration, use a different database.
if app.config['DEBUG']:
database = SqliteDatabase('local.db')
elif app.config['TESTING']:
database = SqliteDatabase(':memory:')
else:
database = PostgresqlDatabase('mega_production_db')
# Configure our proxy to use the db we specified in config.
database_proxy.initialize(database)
WARNING:
Only use this method if your actual database driver varies at run-time. For instance, if your tests
and local dev environment run on SQLite, but your deployed app uses PostgreSQL, you can use the Proxy
to swap out engines at run-time.
However, if it is only connection values that vary at run-time, such as the path to the database file,
or the database host, you should instead use Database.init(). See Run-time database configuration for
more details.
Connection Management
To open a connection to a database, use the Database.connect() method:
>>> db = SqliteDatabase(':memory:') # In-memory SQLite database.
>>> db.connect()
True
If we try to call connect() on an already-open database, we get a OperationalError:
>>> db.connect()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/home/charles/pypath/peewee.py", line 2390, in connect
raise OperationalError('Connection already opened.')
peewee.OperationalError: Connection already opened.
To prevent this exception from being raised, we can call connect() with an additional argument,
reuse_if_open:
>>> db.close() # Close connection.
True
>>> db.connect()
True
>>> db.connect(reuse_if_open=True)
False
Note that the call to connect() returns False if the database connection was already open.
To close a connection, use the Database.close() method:
>>> db.close()
True
Calling close() on an already-closed connection will not result in an exception, but will return False:
>>> db.connect() # Open connection.
True
>>> db.close() # Close connection.
True
>>> db.close() # Connection already closed, returns False.
False
You can test whether the database is closed using the Database.is_closed() method:
>>> db.is_closed()
True
A note of caution
Although it is not necessary to explicitly connect to the database before using it, managing connections
explicitly is considered a best practice. For example, if the connection fails, the exception will be
caught when the connection is being opened, rather than some arbitrary time later when a query is
executed. Furthermore, if you are using a connection pool, it is necessary to call connect() and close()
to ensure connections are recycled properly.
Thread Safety
Peewee keeps track of the connection state using thread-local storage, making the Peewee Database object
safe to use with multiple threads. Each thread will have it's own connection, and as a result any given
thread will only have a single connection open at a given time.
Context managers
The database object itself can be used as a context-manager, which opens a connection for the duration of
the wrapped block of code. Additionally, a transaction is opened at the start of the wrapped block and
committed before the connection is closed (unless an error occurs, in which case the transaction is
rolled back).
>>> db.is_closed()
True
>>> with db:
... print(db.is_closed()) # db is open inside context manager.
...
False
>>> db.is_closed() # db is closed.
True
If you want to manage transactions separately, you can use the Database.connection_context() context
manager.
>>> with db.connection_context():
... # db connection is open.
... pass
...
>>> db.is_closed() # db connection is closed.
True
The connection_context() method can also be used as a decorator:
@db.connection_context()
def prepare_database():
# DB connection will be managed by the decorator, which opens
# a connection, calls function, and closes upon returning.
db.create_tables(MODELS) # Create schema.
load_fixture_data(db)
DB-API Connection Object
To obtain a reference to the underlying DB-API 2.0 connection, use the Database.connection() method. This
method will return the currently-open connection object, if one exists, otherwise it will open a new
connection.
>>> db.connection()
<sqlite3.Connection object at 0x7f94e9362f10>
Connection Pooling
Connection pooling is provided by the pool module, included in the playhouse extensions library. The pool
supports:
• Timeout after which connections will be recycled.
• Upper bound on the number of open connections.
from playhouse.pool import PooledPostgresqlExtDatabase
db = PooledPostgresqlExtDatabase(
'my_database',
max_connections=8,
stale_timeout=300,
user='postgres')
class BaseModel(Model):
class Meta:
database = db
The following pooled database classes are available:
• PooledPostgresqlDatabase
• PooledPostgresqlExtDatabase
• PooledMySQLDatabase
• PooledSqliteDatabase
• PooledSqliteExtDatabase
For an in-depth discussion of peewee's connection pool, see the pool section of the playhouse
documentation.
Testing Peewee Applications
When writing tests for an application that uses Peewee, it may be desirable to use a special database for
tests. Another common practice is to run tests against a clean database, which means ensuring tables are
empty at the start of each test.
To bind your models to a database at run-time, you can use the following methods:
• Database.bind_ctx(), which returns a context-manager that will bind the given models to the database
instance for the duration of the wrapped block.
• Model.bind_ctx(), which likewise returns a context-manager that binds the model (and optionally its
dependencies) to the given database for the duration of the wrapped block.
• Database.bind(), which is a one-time operation that binds the models (and optionally its dependencies)
to the given database.
• Model.bind(), which is a one-time operation that binds the model (and optionally its dependencies) to
the given database.
Depending on your use-case, one of these options may make more sense. For the examples below, I will use
Model.bind().
Example test-case setup:
# tests.py
import unittest
from my_app.models import EventLog, Relationship, Tweet, User
MODELS = [User, Tweet, EventLog, Relationship]
# use an in-memory SQLite for tests.
test_db = SqliteDatabase(':memory:')
class BaseTestCase(unittest.TestCase):
def setUp(self):
# Bind model classes to test db. Since we have a complete list of
# all models, we do not need to recursively bind dependencies.
test_db.bind(MODELS, bind_refs=False, bind_backrefs=False)
test_db.connect()
test_db.create_tables(MODELS)
def tearDown(self):
# Not strictly necessary since SQLite in-memory databases only live
# for the duration of the connection, and in the next step we close
# the connection...but a good practice all the same.
test_db.drop_tables(MODELS)
# Close connection to db.
test_db.close()
# If we wanted, we could re-bind the models to their original
# database here. But for tests this is probably not necessary.
As an aside, and speaking from experience, I recommend testing your application using the same database
backend you use in production, so as to avoid any potential compatibility issues.
If you'd like to see some more examples of how to run tests using Peewee, check out Peewee's own
test-suite.
Async with Gevent
gevent is recommended for doing asynchronous I/O with Postgresql or MySQL. Reasons I prefer gevent:
• No need for special-purpose "loop-aware" re-implementations of everything. Third-party libraries using
asyncio usually have to re-implement layers and layers of code as well as re-implementing the protocols
themselves.
• Gevent allows you to write your application in normal, clean, idiomatic Python. No need to litter every
line with "async", "await" and other noise. No callbacks, futures, tasks, promises. No cruft.
• Gevent works with both Python 2 and Python 3.
• Gevent is Pythonic. Asyncio is an un-pythonic abomination.
Besides monkey-patching socket, no special steps are required if you are using MySQL with a pure Python
driver like pymysql or are using mysql-connector in pure-python mode. MySQL drivers written in C will
require special configuration which is beyond the scope of this document.
For Postgres and psycopg2, which is a C extension, you can use the following code snippet to register
event hooks that will make your connection async:
from gevent.socket import wait_read, wait_write
from psycopg2 import extensions
# Call this function after monkey-patching socket (etc).
def patch_psycopg2():
extensions.set_wait_callback(_psycopg2_gevent_callback)
def _psycopg2_gevent_callback(conn, timeout=None):
while True:
state = conn.poll()
if state == extensions.POLL_OK:
break
elif state == extensions.POLL_READ:
wait_read(conn.fileno(), timeout=timeout)
elif state == extensions.POLL_WRITE:
wait_write(conn.fileno(), timeout=timeout)
else:
raise ValueError('poll() returned unexpected result')
SQLite, because it is embedded in the Python application itself, does not do any socket operations that
would be a candidate for non-blocking. Async has no effect one way or the other on SQLite databases.
Framework Integration
For web applications, it is common to open a connection when a request is received, and to close the
connection when the response is delivered. In this section I will describe how to add hooks to your web
app to ensure the database connection is handled properly.
These steps will ensure that regardless of whether you're using a simple SQLite database, or a pool of
multiple Postgres connections, peewee will handle the connections correctly.
NOTE:
Applications that receive lots of traffic may benefit from using a connection pool to mitigate the
cost of setting up and tearing down connections on every request.
Flask
Flask and peewee are a great combo and my go-to for projects of any size. Flask provides two hooks which
we will use to open and close our db connection. We'll open the connection when a request is received,
then close it when the response is returned.
from flask import Flask
from peewee import *
database = SqliteDatabase('my_app.db')
app = Flask(__name__)
# This hook ensures that a connection is opened to handle any queries
# generated by the request.
@app.before_request
def _db_connect():
database.connect()
# This hook ensures that the connection is closed when we've finished
# processing the request.
@app.teardown_request
def _db_close(exc):
if not database.is_closed():
database.close()
Django
While it's less common to see peewee used with Django, it is actually very easy to use the two. To manage
your peewee database connections with Django, the easiest way in my opinion is to add a middleware to
your app. The middleware should be the very first in the list of middlewares, to ensure it runs first
when a request is handled, and last when the response is returned.
If you have a django project named my_blog and your peewee database is defined in the module my_blog.db,
you might add the following middleware class:
# middleware.py
from my_blog.db import database # Import the peewee database instance.
class PeeweeConnectionMiddleware(object):
def process_request(self, request):
database.connect()
def process_response(self, request, response):
if not database.is_closed():
database.close()
return response
To ensure this middleware gets executed, add it to your settings module:
# settings.py
MIDDLEWARE_CLASSES = (
# Our custom middleware appears first in the list.
'my_blog.middleware.PeeweeConnectionMiddleware',
# These are the default Django 1.7 middlewares. Yours may differ,
# but the important this is that our Peewee middleware comes first.
'django.middleware.common.CommonMiddleware',
'django.contrib.sessions.middleware.SessionMiddleware',
'django.middleware.csrf.CsrfViewMiddleware',
'django.contrib.auth.middleware.AuthenticationMiddleware',
'django.contrib.messages.middleware.MessageMiddleware',
)
# ... other Django settings ...
Bottle
I haven't used bottle myself, but looking at the documentation I believe the following code should ensure
the database connections are properly managed:
# app.py
from bottle import hook #, route, etc, etc.
from peewee import *
db = SqliteDatabase('my-bottle-app.db')
@hook('before_request')
def _connect_db():
db.connect()
@hook('after_request')
def _close_db():
if not db.is_closed():
db.close()
# Rest of your bottle app goes here.
Web.py
See the documentation for application processors.
db = SqliteDatabase('my_webpy_app.db')
def connection_processor(handler):
db.connect()
try:
return handler()
finally:
if not db.is_closed():
db.close()
app.add_processor(connection_processor)
Tornado
It looks like Tornado's RequestHandler class implements two hooks which can be used to open and close
connections when a request is handled.
from tornado.web import RequestHandler
db = SqliteDatabase('my_db.db')
class PeeweeRequestHandler(RequestHandler):
def prepare(self):
db.connect()
return super(PeeweeRequestHandler, self).prepare()
def on_finish(self):
if not db.is_closed():
db.close()
return super(PeeweeRequestHandler, self).on_finish()
In your app, instead of extending the default RequestHandler, now you can extend PeeweeRequestHandler.
Note that this does not address how to use peewee asynchronously with Tornado or another event loop.
Wheezy.web
The connection handling code can be placed in a middleware.
def peewee_middleware(request, following):
db.connect()
try:
response = following(request)
finally:
if not db.is_closed():
db.close()
return response
app = WSGIApplication(middleware=[
lambda x: peewee_middleware,
# ... other middlewares ...
])
Thanks to GitHub user @tuukkamustonen for submitting this code.
Falcon
The connection handling code can be placed in a middleware component.
import falcon
from peewee import *
database = SqliteDatabase('my_app.db')
class PeeweeConnectionMiddleware(object):
def process_request(self, req, resp):
database.connect()
def process_response(self, req, resp, resource):
if not database.is_closed():
database.close()
application = falcon.API(middleware=[
PeeweeConnectionMiddleware(),
# ... other middlewares ...
])
Pyramid
Set up a Request factory that handles database connection lifetime as follows:
from pyramid.request import Request
db = SqliteDatabase('pyramidapp.db')
class MyRequest(Request):
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
db.connect()
self.add_finished_callback(self.finish)
def finish(self, request):
if not db.is_closed():
db.close()
In your application main() make sure MyRequest is used as request_factory:
def main(global_settings, **settings):
config = Configurator(settings=settings, ...)
config.set_request_factory(MyRequest)
CherryPy
See Publish/Subscribe pattern.
def _db_connect():
db.connect()
def _db_close():
if not db.is_closed():
db.close()
cherrypy.engine.subscribe('before_request', _db_connect)
cherrypy.engine.subscribe('after_request', _db_close)
Sanic
In Sanic, the connection handling code can be placed in the request and response middleware sanic
middleware.
# app.py
@app.middleware('request')
async def handle_request(request):
db.connect()
@app.middleware('response')
async def handle_response(request, response):
if not db.is_closed():
db.close()
Other frameworks
Don't see your framework here? Please open a GitHub ticket and I'll see about adding a section, or better
yet, submit a documentation pull-request.
Executing Queries
SQL queries will typically be executed by calling execute() on a query constructed using the
query-builder APIs (or by simply iterating over a query object in the case of a Select query). For cases
where you wish to execute SQL directly, you can use the Database.execute_sql() method.
db = SqliteDatabase('my_app.db')
db.connect()
# Example of executing a simple query and ignoring the results.
db.execute_sql("ATTACH DATABASE ':memory:' AS cache;")
# Example of iterating over the results of a query using the cursor.
cursor = db.execute_sql('SELECT * FROM users WHERE status = ?', (ACTIVE,))
for row in cursor.fetchall():
# Do something with row, which is a tuple containing column data.
pass
Managing Transactions
Peewee provides several interfaces for working with transactions. The most general is the
Database.atomic() method, which also supports nested transactions. atomic() blocks will be run in a
transaction or savepoint, depending on the level of nesting.
If an exception occurs in a wrapped block, the current transaction/savepoint will be rolled back.
Otherwise the statements will be committed at the end of the wrapped block.
NOTE:
While inside a block wrapped by the atomic() context manager, you can explicitly rollback or commit at
any point by calling Transaction.rollback() or Transaction.commit(). When you do this inside a wrapped
block of code, a new transaction will be started automatically.
with db.atomic() as transaction: # Opens new transaction.
try:
save_some_objects()
except ErrorSavingData:
# Because this block of code is wrapped with "atomic", a
# new transaction will begin automatically after the call
# to rollback().
transaction.rollback()
error_saving = True
create_report(error_saving=error_saving)
# Note: no need to call commit. Since this marks the end of the
# wrapped block of code, the `atomic` context manager will
# automatically call commit for us.
NOTE:
atomic() can be used as either a context manager or a decorator.
Context manager
Using atomic as context manager:
db = SqliteDatabase(':memory:')
with db.atomic() as txn:
# This is the outer-most level, so this block corresponds to
# a transaction.
User.create(username='charlie')
with db.atomic() as nested_txn:
# This block corresponds to a savepoint.
User.create(username='huey')
# This will roll back the above create() query.
nested_txn.rollback()
User.create(username='mickey')
# When the block ends, the transaction is committed (assuming no error
# occurs). At that point there will be two users, "charlie" and "mickey".
You can use the atomic method to perform get or create operations as well:
try:
with db.atomic():
user = User.create(username=username)
return 'Success'
except peewee.IntegrityError:
return 'Failure: %s is already in use.' % username
Decorator
Using atomic as a decorator:
@db.atomic()
def create_user(username):
# This statement will run in a transaction. If the caller is already
# running in an `atomic` block, then a savepoint will be used instead.
return User.create(username=username)
create_user('charlie')
Nesting Transactions
atomic() provides transparent nesting of transactions. When using atomic(), the outer-most call will be
wrapped in a transaction, and any nested calls will use savepoints.
with db.atomic() as txn:
perform_operation()
with db.atomic() as nested_txn:
perform_another_operation()
Peewee supports nested transactions through the use of savepoints (for more information, see
savepoint()).
Explicit transaction
If you wish to explicitly run code in a transaction, you can use transaction(). Like atomic(),
transaction() can be used as a context manager or as a decorator.
If an exception occurs in a wrapped block, the transaction will be rolled back. Otherwise the statements
will be committed at the end of the wrapped block.
db = SqliteDatabase(':memory:')
with db.transaction() as txn:
# Delete the user and their associated tweets.
user.delete_instance(recursive=True)
Transactions can be explicitly committed or rolled-back within the wrapped block. When this happens, a
new transaction will be started.
with db.transaction() as txn:
User.create(username='mickey')
txn.commit() # Changes are saved and a new transaction begins.
User.create(username='huey')
# Roll back. "huey" will not be saved, but since "mickey" was already
# committed, that row will remain in the database.
txn.rollback()
with db.transaction() as txn:
User.create(username='whiskers')
# Roll back changes, which removes "whiskers".
txn.rollback()
# Create a new row for "mr. whiskers" which will be implicitly committed
# at the end of the `with` block.
User.create(username='mr. whiskers')
NOTE:
If you attempt to nest transactions with peewee using the transaction() context manager, only the
outer-most transaction will be used. However if an exception occurs in a nested block, this can lead
to unpredictable behavior, so it is strongly recommended that you use atomic().
Explicit Savepoints
Just as you can explicitly create transactions, you can also explicitly create savepoints using the
savepoint() method. Savepoints must occur within a transaction, but can be nested arbitrarily deep.
with db.transaction() as txn:
with db.savepoint() as sp:
User.create(username='mickey')
with db.savepoint() as sp2:
User.create(username='zaizee')
sp2.rollback() # "zaizee" will not be saved, but "mickey" will be.
WARNING:
If you manually commit or roll back a savepoint, a new savepoint will not automatically be created.
This differs from the behavior of transaction, which will automatically open a new transaction after
manual commit/rollback.
Autocommit Mode
By default, Peewee operates in autocommit mode, such that any statements executed outside of a
transaction are run in their own transaction. To group multiple statements into a transaction, Peewee
provides the atomic() context-manager/decorator. This should cover all use-cases, but in the unlikely
event you want to temporarily disable Peewee's transaction management completely, you can use the
Database.manual_commit() context-manager/decorator.
Here is how you might emulate the behavior of the transaction() context manager:
with db.manual_commit():
db.begin() # Have to begin transaction explicitly.
try:
user.delete_instance(recursive=True)
except:
db.rollback() # Rollback! An error occurred.
raise
else:
try:
db.commit() # Commit changes.
except:
db.rollback()
raise
Again -- I don't anticipate anyone needing this, but it's here just in case.
Database Errors
The Python DB-API 2.0 spec describes several types of exceptions. Because most database drivers have
their own implementations of these exceptions, Peewee simplifies things by providing its own wrappers
around any implementation-specific exception classes. That way, you don't need to worry about importing
any special exception classes, you can just use the ones from peewee:
• DatabaseError
• DataError
• IntegrityError
• InterfaceError
• InternalError
• NotSupportedError
• OperationalError
• ProgrammingError
NOTE:
All of these error classes extend PeeweeException.
Logging queries
All queries are logged to the peewee namespace using the standard library logging module. Queries are
logged using the DEBUG level. If you're interested in doing something with the queries, you can simply
register a handler.
# Print all queries to stderr.
import logging
logger = logging.getLogger('peewee')
logger.addHandler(logging.StreamHandler())
logger.setLevel(logging.DEBUG)
Adding a new Database Driver
Peewee comes with built-in support for Postgres, MySQL and SQLite. These databases are very popular and
run the gamut from fast, embeddable databases to heavyweight servers suitable for large-scale
deployments. That being said, there are a ton of cool databases out there and adding support for your
database-of-choice should be really easy, provided the driver supports the DB-API 2.0 spec.
The DB-API 2.0 spec should be familiar to you if you've used the standard library sqlite3 driver,
psycopg2 or the like. Peewee currently relies on a handful of parts:
• Connection.commit
• Connection.execute
• Connection.rollback
• Cursor.description
• Cursor.fetchone
These methods are generally wrapped up in higher-level abstractions and exposed by the Database, so even
if your driver doesn't do these exactly you can still get a lot of mileage out of peewee. An example is
the apsw sqlite driver in the "playhouse" module.
The first thing is to provide a subclass of Database that will open a connection.
from peewee import Database
import foodb # Our fictional DB-API 2.0 driver.
class FooDatabase(Database):
def _connect(self, database, **kwargs):
return foodb.connect(database, **kwargs)
The Database provides a higher-level API and is responsible for executing queries, creating tables and
indexes, and introspecting the database to get lists of tables. The above implementation is the absolute
minimum needed, though some features will not work -- for best results you will want to additionally add
a method for extracting a list of tables and indexes for a table from the database. We'll pretend that
FooDB is a lot like MySQL and has special "SHOW" statements:
class FooDatabase(Database):
def _connect(self, database, **kwargs):
return foodb.connect(database, **kwargs)
def get_tables(self):
res = self.execute('SHOW TABLES;')
return [r[0] for r in res.fetchall()]
Other things the database handles that are not covered here include:
• last_insert_id() and rows_affected()
• param and quote, which tell the SQL-generating code how to add parameter placeholders and quote entity
names.
• field_types for mapping data-types like INT or TEXT to their vendor-specific type names.
• operations for mapping operations such as "LIKE/ILIKE" to their database equivalent
Refer to the Database API reference or the source code. for details.
NOTE:
If your driver conforms to the DB-API 2.0 spec, there shouldn't be much work needed to get up and
running.
Our new database can be used just like any of the other database subclasses:
from peewee import *
from foodb_ext import FooDatabase
db = FooDatabase('my_database', user='foo', password='secret')
class BaseModel(Model):
class Meta:
database = db
class Blog(BaseModel):
title = CharField()
contents = TextField()
pub_date = DateTimeField()
Models and Fields
Model classes, Field instances and model instances all map to database concepts:
┌───────────────┬─────────────────────────┐
│Thing │ Corresponds to... │
├───────────────┼─────────────────────────┤
│Model class │ Database table │
├───────────────┼─────────────────────────┤
│Field instance │ Column on a table │
├───────────────┼─────────────────────────┤
│Model instance │ Row in a database table │
└───────────────┴─────────────────────────┘
The following code shows the typical way you will define your database connection and model classes.
from peewee import *
db = SqliteDatabase('my_app.db')
class BaseModel(Model):
class Meta:
database = db
class User(BaseModel):
username = CharField(unique=True)
class Tweet(BaseModel):
user = ForeignKeyField(User, backref='tweets')
message = TextField()
created_date = DateTimeField(default=datetime.datetime.now)
is_published = BooleanField(default=True)
1. Create an instance of a Database.
db = SqliteDatabase('my_app.db')
The db object will be used to manage the connections to the Sqlite database. In this example we're
using SqliteDatabase, but you could also use one of the other database engines.
2. Create a base model class which specifies our database.
class BaseModel(Model):
class Meta:
database = db
It is good practice to define a base model class which establishes the database connection. This
makes your code DRY as you will not have to specify the database for subsequent models.
Model configuration is kept namespaced in a special class called Meta. This convention is borrowed
from Django. Meta configuration is passed on to subclasses, so our project's models will all
subclass BaseModel. There are many different attributes you can configure using Model.Meta.
3. Define a model class.
class User(BaseModel):
username = CharField(unique=True)
Model definition uses the declarative style seen in other popular ORMs like SQLAlchemy or Django.
Note that we are extending the BaseModel class so the User model will inherit the database
connection.
We have explicitly defined a single username column with a unique constraint. Because we have not
specified a primary key, peewee will automatically add an auto-incrementing integer primary key
field named id.
NOTE:
If you would like to start using peewee with an existing database, you can use pwiz to automatically
generate model definitions.
Fields
The Field class is used to describe the mapping of Model attributes to database columns. Each field type
has a corresponding SQL storage class (i.e. varchar, int), and conversion between python data types and
underlying storage is handled transparently.
When creating a Model class, fields are defined as class attributes. This should look familiar to users
of the django framework. Here's an example:
class User(Model):
username = CharField()
join_date = DateTimeField()
about_me = TextField()
In the above example, because none of the fields are initialized with primary_key=True, an
auto-incrementing primary key will automatically be created and named "id".
There is one special type of field, ForeignKeyField, which allows you to represent foreign-key
relationships between models in an intuitive way:
class Message(Model):
user = ForeignKeyField(User, backref='messages')
body = TextField()
send_date = DateTimeField(default=datetime.datetime.now)
This allows you to write code like the following:
>>> print(some_message.user.username)
Some User
>>> for message in some_user.messages:
... print(message.body)
some message
another message
yet another message
NOTE:
Refer to the relationships document for an in-depth discussion of foreign-keys, joins and
relationships between models.
For full documentation on fields, see the Fields API notes
Field types table
┌──────────────────┬───────────────┬──────────────────┬──────────────────┐
│Field Type │ Sqlite │ Postgresql │ MySQL │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│IntegerField │ integer │ integer │ integer │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│BigIntegerField │ integer │ bigint │ bigint │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│SmallIntegerField │ integer │ smallint │ smallint │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│AutoField │ integer │ serial │ integer │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│BigAutoField │ integer │ bigserial │ bigint │
└──────────────────┴───────────────┴──────────────────┴──────────────────┘
│IdentityField │ not supported │ int identity │ not supported │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│FloatField │ real │ real │ real │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│DoubleField │ real │ double precision │ double precision │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│DecimalField │ decimal │ numeric │ numeric │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│CharField │ varchar │ varchar │ varchar │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│FixedCharField │ char │ char │ char │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│TextField │ text │ text │ longtext │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│BlobField │ blob │ bytea │ blob │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│BitField │ integer │ bigint │ bigint │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│BigBitField │ blob │ bytea │ blob │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│UUIDField │ text │ uuid │ varchar(40) │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│BinaryUUIDField │ blob │ bytea │ varbinary(16) │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│DateTimeField │ datetime │ timestamp │ datetime │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│DateField │ date │ date │ date │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│TimeField │ time │ time │ time │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│TimestampField │ integer │ integer │ integer │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│IPField │ integer │ bigint │ bigint │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│BooleanField │ integer │ boolean │ bool │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│BareField │ untyped │ not supported │ not supported │
├──────────────────┼───────────────┼──────────────────┼──────────────────┤
│ForeignKeyField │ integer │ integer │ integer │
└──────────────────┴───────────────┴──────────────────┴──────────────────┘
NOTE:
Don't see the field you're looking for in the above table? It's easy to create custom field types and
use them with your models.
• Creating a custom field
• Database, particularly the fields parameter.
Field initialization arguments
Parameters accepted by all field types and their default values:
• null = False -- allow null values
• index = False -- create an index on this column
• unique = False -- create a unique index on this column. See also adding composite indexes.
• column_name = None -- explicitly specify the column name in the database.
• default = None -- any value or callable to use as a default for uninitialized models
• primary_key = False -- primary key for the table
• constraints = None - one or more constraints, e.g. [Check('price > 0')]
• sequence = None -- sequence name (if backend supports it)
• collation = None -- collation to use for ordering the field / index
• unindexed = False -- indicate field on virtual table should be unindexed (SQLite-only)
• choices = None -- optional iterable containing 2-tuples of value, display
• help_text = None -- string representing any helpful text for this field
• verbose_name = None -- string representing the "user-friendly" name of this field
Some fields take special parameters...
┌────────────────┬───────────────────────────────────────┐
│Field type │ Special Parameters │
├────────────────┼───────────────────────────────────────┤
│CharField │ max_length │
├────────────────┼───────────────────────────────────────┤
│FixedCharField │ max_length │
├────────────────┼───────────────────────────────────────┤
│DateTimeField │ formats │
├────────────────┼───────────────────────────────────────┤
│DateField │ formats │
├────────────────┼───────────────────────────────────────┤
│TimeField │ formats │
├────────────────┼───────────────────────────────────────┤
│TimestampField │ resolution, utc │
├────────────────┼───────────────────────────────────────┤
│DecimalField │ max_digits, decimal_places, │
│ │ auto_round, rounding │
├────────────────┼───────────────────────────────────────┤
│ForeignKeyField │ model, field, backref, on_delete, │
│ │ on_update, deferrable │
├────────────────┼───────────────────────────────────────┤
│BareField │ adapt │
└────────────────┴───────────────────────────────────────┘
NOTE:
Both default and choices could be implemented at the database level as DEFAULT and CHECK CONSTRAINT
respectively, but any application change would require a schema change. Because of this, default is
implemented purely in python and choices are not validated but exist for metadata purposes only.
To add database (server-side) constraints, use the constraints parameter.
Default field values
Peewee can provide default values for fields when objects are created. For example to have an
IntegerField default to zero rather than NULL, you could declare the field with a default value:
class Message(Model):
context = TextField()
read_count = IntegerField(default=0)
In some instances it may make sense for the default value to be dynamic. A common scenario is using the
current date and time. Peewee allows you to specify a function in these cases, whose return value will be
used when the object is created. Note we only provide the function, we do not actually call it:
class Message(Model):
context = TextField()
timestamp = DateTimeField(default=datetime.datetime.now)
NOTE:
If you are using a field that accepts a mutable type (list, dict, etc), and would like to provide a
default, it is a good idea to wrap your default value in a simple function so that multiple model
instances are not sharing a reference to the same underlying object:
def house_defaults():
return {'beds': 0, 'baths': 0}
class House(Model):
number = TextField()
street = TextField()
attributes = JSONField(default=house_defaults)
The database can also provide the default value for a field. While peewee does not explicitly provide an
API for setting a server-side default value, you can use the constraints parameter to specify the server
default:
class Message(Model):
context = TextField()
timestamp = DateTimeField(constraints=[SQL('DEFAULT CURRENT_TIMESTAMP')])
NOTE:
Remember: when using the default parameter, the values are set by Peewee rather than being a part of
the actual table and column definition.
ForeignKeyField
ForeignKeyField is a special field type that allows one model to reference another. Typically a foreign
key will contain the primary key of the model it relates to (but you can specify a particular column by
specifying a field).
Foreign keys allow data to be normalized. In our example models, there is a foreign key from Tweet to
User. This means that all the users are stored in their own table, as are the tweets, and the foreign key
from tweet to user allows each tweet to point to a particular user object.
NOTE:
Refer to the relationships document for an in-depth discussion of foreign keys, joins and
relationships between models.
In peewee, accessing the value of a ForeignKeyField will return the entire related object, e.g.:
tweets = (Tweet
.select(Tweet, User)
.join(User)
.order_by(Tweet.create_date.desc()))
for tweet in tweets:
print(tweet.user.username, tweet.message)
In the example above the User data was selected as part of the query. For more examples of this
technique, see the Avoiding N+1 document.
If we did not select the User, though, then an additional query would be issued to fetch the associated
User data:
tweets = Tweet.select().order_by(Tweet.create_date.desc())
for tweet in tweets:
# WARNING: an additional query will be issued for EACH tweet
# to fetch the associated User data.
print(tweet.user.username, tweet.message)
Sometimes you only need the associated primary key value from the foreign key column. In this case,
Peewee follows the convention established by Django, of allowing you to access the raw foreign key value
by appending "_id" to the foreign key field's name:
tweets = Tweet.select()
for tweet in tweets:
# Instead of "tweet.user", we will just get the raw ID value stored
# in the column.
print(tweet.user_id, tweet.message)
ForeignKeyField allows for a backreferencing property to be bound to the target model. Implicitly, this
property will be named classname_set, where classname is the lowercase name of the class, but can be
overridden using the parameter backref:
class Message(Model):
from_user = ForeignKeyField(User, backref='outbox')
to_user = ForeignKeyField(User, backref='inbox')
text = TextField()
for message in some_user.outbox:
# We are iterating over all Messages whose from_user is some_user.
print(message)
for message in some_user.inbox:
# We are iterating over all Messages whose to_user is some_user
print(message)
DateTimeField, DateField and TimeField
The three fields devoted to working with dates and times have special properties which allow access to
things like the year, month, hour, etc.
DateField has properties for:
• year
• month
• day
TimeField has properties for:
• hour
• minute
• second
DateTimeField has all of the above.
These properties can be used just like any other expression. Let's say we have an events calendar and
want to highlight all the days in the current month that have an event attached:
# Get the current time.
now = datetime.datetime.now()
# Get days that have events for the current month.
Event.select(Event.event_date.day.alias('day')).where(
(Event.event_date.year == now.year) &
(Event.event_date.month == now.month))
NOTE:
SQLite does not have a native date type, so dates are stored in formatted text columns. To ensure that
comparisons work correctly, the dates need to be formatted so they are sorted lexicographically. That
is why they are stored, by default, as YYYY-MM-DD HH:MM:SS.
BitField and BigBitField
The BitField and BigBitField are new as of 3.0.0. The former provides a subclass of IntegerField that is
suitable for storing feature toggles as an integer bitmask. The latter is suitable for storing a bitmap
for a large data-set, e.g. expressing membership or bitmap-type data.
As an example of using BitField, let's say we have a Post model and we wish to store certain True/False
flags about how the post. We could store all these feature toggles in their own BooleanField objects, or
we could use BitField instead:
class Post(Model):
content = TextField()
flags = BitField()
is_favorite = flags.flag(1)
is_sticky = flags.flag(2)
is_minimized = flags.flag(4)
is_deleted = flags.flag(8)
Using these flags is quite simple:
>>> p = Post()
>>> p.is_sticky = True
>>> p.is_minimized = True
>>> print(p.flags) # Prints 4 | 2 --> "6"
6
>>> p.is_favorite
False
>>> p.is_sticky
True
We can also use the flags on the Post class to build expressions in queries:
# Generates a WHERE clause that looks like:
# WHERE (post.flags & 1 != 0)
favorites = Post.select().where(Post.is_favorite)
# Query for sticky + favorite posts:
sticky_faves = Post.select().where(Post.is_sticky & Post.is_favorite)
Since the BitField is stored in an integer, there is a maximum of 64 flags you can represent (64-bits is
common size of integer column). For storing arbitrarily large bitmaps, you can instead use BigBitField,
which uses an automatically managed buffer of bytes, stored in a BlobField.
Example usage:
class Bitmap(Model):
data = BigBitField()
bitmap = Bitmap()
# Sets the ith bit, e.g. the 1st bit, the 11th bit, the 63rd, etc.
bits_to_set = (1, 11, 63, 31, 55, 48, 100, 99)
for bit_idx in bits_to_set:
bitmap.data.set_bit(bit_idx)
# We can test whether a bit is set using "is_set":
assert bitmap.data.is_set(11)
assert not bitmap.data.is_set(12)
# We can clear a bit:
bitmap.data.clear_bit(11)
assert not bitmap.data.is_set(11)
# We can also "toggle" a bit. Recall that the 63rd bit was set earlier.
assert bitmap.data.toggle_bit(63) is False
assert bitmap.data.toggle_bit(63) is True
assert bitmap.data.is_set(63)
BareField
The BareField class is intended to be used only with SQLite. Since SQLite uses dynamic typing and
data-types are not enforced, it can be perfectly fine to declare fields without any data-type. In those
cases you can use BareField. It is also common for SQLite virtual tables to use meta-columns or untyped
columns, so for those cases as well you may wish to use an untyped field (although for full-text search,
you should use SearchField instead!).
BareField accepts a special parameter adapt. This parameter is a function that takes a value coming from
the database and converts it into the appropriate Python type. For instance, if you have a virtual table
with an un-typed column but you know that it will return int objects, you can specify adapt=int.
Example:
db = SqliteDatabase(':memory:')
class Junk(Model):
anything = BareField()
class Meta:
database = db
# Store multiple data-types in the Junk.anything column:
Junk.create(anything='a string')
Junk.create(anything=12345)
Junk.create(anything=3.14159)
Creating a custom field
It is easy to add support for custom field types in peewee. In this example we will create a UUID field
for postgresql (which has a native UUID column type).
To add a custom field type you need to first identify what type of column the field data will be stored
in. If you just want to add python behavior atop, say, a decimal field (for instance to make a currency
field) you would just subclass DecimalField. On the other hand, if the database offers a custom column
type you will need to let peewee know. This is controlled by the Field.field_type attribute.
NOTE:
Peewee ships with a UUIDField, the following code is intended only as an example.
Let's start by defining our UUID field:
class UUIDField(Field):
field_type = 'uuid'
We will store the UUIDs in a native UUID column. Since psycopg2 treats the data as a string by default,
we will add two methods to the field to handle:
• The data coming out of the database to be used in our application
• The data from our python app going into the database
import uuid
class UUIDField(Field):
field_type = 'uuid'
def db_value(self, value):
return value.hex # convert UUID to hex string.
def python_value(self, value):
return uuid.UUID(value) # convert hex string to UUID
This step is optional. By default, the field_type value will be used for the columns data-type in the
database schema. If you need to support multiple databases which use different data-types for your
field-data, we need to let the database know how to map this uuid label to an actual uuid column type in
the database. Specify the overrides in the Database constructor:
# Postgres, we use UUID data-type.
db = PostgresqlDatabase('my_db', field_types={'uuid': 'uuid'})
# Sqlite doesn't have a UUID type, so we use text type.
db = SqliteDatabase('my_db', field_types={'uuid': 'text'})
That is it! Some fields may support exotic operations, like the postgresql HStore field acts like a
key/value store and has custom operators for things like contains and update. You can specify custom
operations as well. For example code, check out the source code for the HStoreField, in
playhouse.postgres_ext.
Field-naming conflicts
Model classes implement a number of class- and instance-methods, for example Model.save() or
Model.create(). If you declare a field whose name coincides with a model method, it could cause problems.
Consider:
class LogEntry(Model):
event = TextField()
create = TimestampField() # Uh-oh.
update = TimestampField() # Uh-oh.
To avoid this problem while still using the desired column name in the database schema, explicitly
specify the column_name while providing an alternative name for the field attribute:
class LogEntry(Model):
event = TextField()
create_ = TimestampField(column_name='create')
update_ = TimestampField(column_name='update')
Creating model tables
In order to start using our models, its necessary to open a connection to the database and create the
tables first. Peewee will run the necessary CREATE TABLE queries, additionally creating any constraints
and indexes.
# Connect to our database.
db.connect()
# Create the tables.
db.create_tables([User, Tweet])
NOTE:
Strictly speaking, it is not necessary to call connect() but it is good practice to be explicit. That
way if something goes wrong, the error occurs at the connect step, rather than some arbitrary time
later.
NOTE:
By default, Peewee includes an IF NOT EXISTS clause when creating tables. If you want to disable this,
specify safe=False.
After you have created your tables, if you choose to modify your database schema (by adding, removing or
otherwise changing the columns) you will need to either:
• Drop the table and re-create it.
• Run one or more ALTER TABLE queries. Peewee comes with a schema migration tool which can greatly
simplify this. Check the schema migrations docs for details.
Model options and table metadata
In order not to pollute the model namespace, model-specific configuration is placed in a special class
called Meta (a convention borrowed from the django framework):
from peewee import *
contacts_db = SqliteDatabase('contacts.db')
class Person(Model):
name = CharField()
class Meta:
database = contacts_db
This instructs peewee that whenever a query is executed on Person to use the contacts database.
NOTE:
Take a look at the sample models - you will notice that we created a BaseModel that defined the
database, and then extended. This is the preferred way to define a database and create models.
Once the class is defined, you should not access ModelClass.Meta, but instead use ModelClass._meta:
>>> Person.Meta
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: type object 'Person' has no attribute 'Meta'
>>> Person._meta
<peewee.ModelOptions object at 0x7f51a2f03790>
The ModelOptions class implements several methods which may be of use for retrieving model metadata (such
as lists of fields, foreign key relationships, and more).
>>> Person._meta.fields
{'id': <peewee.PrimaryKeyField object at 0x7f51a2e92750>,
'name': <peewee.CharField object at 0x7f51a2f0a510>}
>>> Person._meta.primary_key
<peewee.PrimaryKeyField object at 0x7f51a2e92750>
>>> Person._meta.database
<peewee.SqliteDatabase object at 0x7f519bff6dd0>
There are several options you can specify as Meta attributes. While most options are inheritable, some
are table-specific and will not be inherited by subclasses.
┌───────────────────┬──────────────────────────────┬──────────────┐
│Option │ Meaning │ Inheritable? │
├───────────────────┼──────────────────────────────┼──────────────┤
│database │ database for model │ yes │
├───────────────────┼──────────────────────────────┼──────────────┤
│table_name │ name of the table to store │ no │
│ │ data │ │
├───────────────────┼──────────────────────────────┼──────────────┤
│table_function │ function to generate table │ yes │
│ │ name dynamically │ │
├───────────────────┼──────────────────────────────┼──────────────┤
│indexes │ a list of fields to index │ yes │
├───────────────────┼──────────────────────────────┼──────────────┤
│primary_key │ a CompositeKey instance │ yes │
└───────────────────┴──────────────────────────────┴──────────────┘
│constraints │ a list of table constraints │ yes │
├───────────────────┼──────────────────────────────┼──────────────┤
│schema │ the database schema for the │ yes │
│ │ model │ │
├───────────────────┼──────────────────────────────┼──────────────┤
│only_save_dirty │ when calling model.save(), │ yes │
│ │ only save dirty fields │ │
├───────────────────┼──────────────────────────────┼──────────────┤
│options │ dictionary of options for │ yes │
│ │ create table extensions │ │
├───────────────────┼──────────────────────────────┼──────────────┤
│temporary │ indicate temporary table │ yes │
├───────────────────┼──────────────────────────────┼──────────────┤
│legacy_table_names │ use legacy table name │ yes │
│ │ generation (enabled by │ │
│ │ default) │ │
├───────────────────┼──────────────────────────────┼──────────────┤
│table_alias │ an alias to use for the │ no │
│ │ table in queries │ │
├───────────────────┼──────────────────────────────┼──────────────┤
│depends_on │ indicate this table depends │ no │
│ │ on another for creation │ │
├───────────────────┼──────────────────────────────┼──────────────┤
│without_rowid │ indicate table should not │ no │
│ │ have rowid (SQLite only) │ │
└───────────────────┴──────────────────────────────┴──────────────┘
Here is an example showing inheritable versus non-inheritable attributes:
>>> db = SqliteDatabase(':memory:')
>>> class ModelOne(Model):
... class Meta:
... database = db
... table_name = 'model_one_tbl'
...
>>> class ModelTwo(ModelOne):
... pass
...
>>> ModelOne._meta.database is ModelTwo._meta.database
True
>>> ModelOne._meta.table_name == ModelTwo._meta.table_name
False
Meta.primary_key
The Meta.primary_key attribute is used to specify either a CompositeKey or to indicate that the model has
no primary key. Composite primary keys are discussed in more detail here: Composite primary keys.
To indicate that a model should not have a primary key, then set primary_key = False.
Examples:
class BlogToTag(Model):
"""A simple "through" table for many-to-many relationship."""
blog = ForeignKeyField(Blog)
tag = ForeignKeyField(Tag)
class Meta:
primary_key = CompositeKey('blog', 'tag')
class NoPrimaryKey(Model):
data = IntegerField()
class Meta:
primary_key = False
Table Names
By default Peewee will automatically generate a table name based on the name of your model class. The way
the table-name is generated depends on the value of Meta.legacy_table_names. By default,
legacy_table_names=True so as to avoid breaking backwards-compatibility. However, if you wish to use the
new and improved table-name generation, you can specify legacy_table_names=False.
This table shows the differences in how a model name is converted to a SQL table name, depending on the
value of legacy_table_names:
┌─────────────────┬─────────────────────────┬──────────────────────────┐
│Model name │ legacy_table_names=True │ legacy_table_names=False │
│ │ │ (new) │
├─────────────────┼─────────────────────────┼──────────────────────────┤
│User │ user │ user │
├─────────────────┼─────────────────────────┼──────────────────────────┤
│UserProfile │ userprofile │ user_profile │
├─────────────────┼─────────────────────────┼──────────────────────────┤
│APIResponse │ apiresponse │ api_response │
├─────────────────┼─────────────────────────┼──────────────────────────┤
│WebHTTPRequest │ webhttprequest │ web_http_request │
├─────────────────┼─────────────────────────┼──────────────────────────┤
│mixedCamelCase │ mixedcamelcase │ mixed_camel_case │
├─────────────────┼─────────────────────────┼──────────────────────────┤
│Name2Numbers3XYZ │ name2numbers3xyz │ name2_numbers3_xyz │
└─────────────────┴─────────────────────────┴──────────────────────────┘
ATTENTION:
To preserve backwards-compatibility, the current release (Peewee 3.x) specifies
legacy_table_names=True by default.
In the next major release (Peewee 4.0), legacy_table_names will have a default value of False.
To explicitly specify the table name for a model class, use the table_name Meta option. This feature can
be useful for dealing with pre-existing database schemas that may have used awkward naming conventions:
class UserProfile(Model):
class Meta:
table_name = 'user_profile_tbl'
If you wish to implement your own naming convention, you can specify the table_function Meta option. This
function will be called with your model class and should return the desired table name as a string.
Suppose our company specifies that table names should be lower-cased and end with "_tbl", we can
implement this as a table function:
def make_table_name(model_class):
model_name = model_class.__name__
return model_name.lower() + '_tbl'
class BaseModel(Model):
class Meta:
table_function = make_table_name
class User(BaseModel):
# table_name will be "user_tbl".
class UserProfile(BaseModel):
# table_name will be "userprofile_tbl".
Indexes and Constraints
Peewee can create indexes on single or multiple columns, optionally including a UNIQUE constraint. Peewee
also supports user-defined constraints on both models and fields.
Single-column indexes and constraints
Single column indexes are defined using field initialization parameters. The following example adds a
unique index on the username field, and a normal index on the email field:
class User(Model):
username = CharField(unique=True)
email = CharField(index=True)
To add a user-defined constraint on a column, you can pass it in using the constraints parameter. You may
wish to specify a default value as part of the schema, or add a CHECK constraint, for example:
class Product(Model):
name = CharField(unique=True)
price = DecimalField(constraints=[Check('price < 10000')])
created = DateTimeField(
constraints=[SQL("DEFAULT (datetime('now'))")])
Multi-column indexes
Multi-column indexes may be defined as Meta attributes using a nested tuple. Each database index is a
2-tuple, the first part of which is a tuple of the names of the fields, the second part a boolean
indicating whether the index should be unique.
class Transaction(Model):
from_acct = CharField()
to_acct = CharField()
amount = DecimalField()
date = DateTimeField()
class Meta:
indexes = (
# create a unique on from/to/date
(('from_acct', 'to_acct', 'date'), True),
# create a non-unique on from/to
(('from_acct', 'to_acct'), False),
)
NOTE:
Remember to add a trailing comma if your tuple of indexes contains only one item:
class Meta:
indexes = (
(('first_name', 'last_name'), True), # Note the trailing comma!
)
Advanced Index Creation
Peewee supports a more structured API for declaring indexes on a model using the Model.add_index() method
or by directly using the ModelIndex helper class.
Examples:
class Article(Model):
name = TextField()
timestamp = TimestampField()
status = IntegerField()
flags = IntegerField()
# Add an index on "name" and "timestamp" columns.
Article.add_index(Article.name, Article.timestamp)
# Add a partial index on name and timestamp where status = 1.
Article.add_index(Article.name, Article.timestamp,
where=(Article.status == 1))
# Create a unique index on timestamp desc, status & 4.
idx = Article.index(
Article.timestamp.desc(),
Article.flags.bin_and(4),
unique=True)
Article.add_index(idx)
WARNING:
SQLite does not support parameterized CREATE INDEX queries. This means that when using SQLite to
create an index that involves an expression or scalar value, you will need to declare the index using
the SQL helper:
# SQLite does not support parameterized CREATE INDEX queries, so
# we declare it manually.
Article.add_index(SQL('CREATE INDEX ...'))
See add_index() for details.
For more information, see:
• Model.add_index()
• Model.index()
• ModelIndex
• Index
Table constraints
Peewee allows you to add arbitrary constraints to your Model, that will be part of the table definition
when the schema is created.
For instance, suppose you have a people table with a composite primary key of two columns, the person's
first and last name. You wish to have another table relate to the people table, and to do this, you will
need to define a foreign key constraint:
class Person(Model):
first = CharField()
last = CharField()
class Meta:
primary_key = CompositeKey('first', 'last')
class Pet(Model):
owner_first = CharField()
owner_last = CharField()
pet_name = CharField()
class Meta:
constraints = [SQL('FOREIGN KEY(owner_first, owner_last) '
'REFERENCES person(first, last)')]
You can also implement CHECK constraints at the table level:
class Product(Model):
name = CharField(unique=True)
price = DecimalField()
class Meta:
constraints = [Check('price < 10000')]
Non-integer Primary Keys, Composite Keys and other Tricks
Non-integer primary keys
If you would like use a non-integer primary key (which I generally don't recommend), you can specify
primary_key=True when creating a field. When you wish to create a new instance for a model using a
non-autoincrementing primary key, you need to be sure you save() specifying force_insert=True.
from peewee import *
class UUIDModel(Model):
id = UUIDField(primary_key=True)
Auto-incrementing IDs are, as their name says, automatically generated for you when you insert a new row
into the database. When you call save(), peewee determines whether to do an INSERT versus an UPDATE based
on the presence of a primary key value. Since, with our uuid example, the database driver won't generate
a new ID, we need to specify it manually. When we call save() for the first time, pass in force_insert =
True:
# This works because .create() will specify `force_insert=True`.
obj1 = UUIDModel.create(id=uuid.uuid4())
# This will not work, however. Peewee will attempt to do an update:
obj2 = UUIDModel(id=uuid.uuid4())
obj2.save() # WRONG
obj2.save(force_insert=True) # CORRECT
# Once the object has been created, you can call save() normally.
obj2.save()
NOTE:
Any foreign keys to a model with a non-integer primary key will have a ForeignKeyField use the same
underlying storage type as the primary key they are related to.
Composite primary keys
Peewee has very basic support for composite keys. In order to use a composite key, you must set the
primary_key attribute of the model options to a CompositeKey instance:
class BlogToTag(Model):
"""A simple "through" table for many-to-many relationship."""
blog = ForeignKeyField(Blog)
tag = ForeignKeyField(Tag)
class Meta:
primary_key = CompositeKey('blog', 'tag')
WARNING:
Peewee does not support foreign-keys to models that define a CompositeKey primary key. If you wish to
add a foreign-key to a model that has a composite primary key, replicate the columns on the related
model and add a custom accessor (e.g. a property).
Manually specifying primary keys
Sometimes you do not want the database to automatically generate a value for the primary key, for
instance when bulk loading relational data. To handle this on a one-off basis, you can simply tell peewee
to turn off auto_increment during the import:
data = load_user_csv() # load up a bunch of data
User._meta.auto_increment = False # turn off auto incrementing IDs
with db.atomic():
for row in data:
u = User(id=row[0], username=row[1])
u.save(force_insert=True) # <-- force peewee to insert row
User._meta.auto_increment = True
Although a better way to accomplish the above, without resorting to hacks, is to use the
Model.insert_many() API:
data = load_user_csv()
fields = [User.id, User.username]
with db.atomic():
User.insert_many(data, fields=fields).execute()
If you always want to have control over the primary key, simply do not use the PrimaryKeyField field
type, but use a normal IntegerField (or other column type):
class User(BaseModel):
id = IntegerField(primary_key=True)
username = CharField()
>>> u = User.create(id=999, username='somebody')
>>> u.id
999
>>> User.get(User.username == 'somebody').id
999
Models without a Primary Key
If you wish to create a model with no primary key, you can specify primary_key = False in the inner Meta
class:
class MyData(BaseModel):
timestamp = DateTimeField()
value = IntegerField()
class Meta:
primary_key = False
This will yield the following DDL:
CREATE TABLE "mydata" (
"timestamp" DATETIME NOT NULL,
"value" INTEGER NOT NULL
)
WARNING:
Some model APIs may not work correctly for models without a primary key, for instance save() and
delete_instance() (you can instead use insert(), update() and delete()).
Self-referential foreign keys
When creating a hierarchical structure it is necessary to create a self-referential foreign key which
links a child object to its parent. Because the model class is not defined at the time you instantiate
the self-referential foreign key, use the special string 'self' to indicate a self-referential foreign
key:
class Category(Model):
name = CharField()
parent = ForeignKeyField('self', null=True, backref='children')
As you can see, the foreign key points upward to the parent object and the back-reference is named
children.
ATTENTION:
Self-referential foreign-keys should always be null=True.
When querying against a model that contains a self-referential foreign key you may sometimes need to
perform a self-join. In those cases you can use Model.alias() to create a table reference. Here is how
you might query the category and parent model using a self-join:
Parent = Category.alias()
GrandParent = Category.alias()
query = (Category
.select(Category, Parent)
.join(Parent, on=(Category.parent == Parent.id))
.join(GrandParent, on=(Parent.parent == GrandParent.id))
.where(GrandParent.name == 'some category')
.order_by(Category.name))
Circular foreign key dependencies
Sometimes it happens that you will create a circular dependency between two tables.
NOTE:
My personal opinion is that circular foreign keys are a code smell and should be refactored (by adding
an intermediary table, for instance).
Adding circular foreign keys with peewee is a bit tricky because at the time you are defining either
foreign key, the model it points to will not have been defined yet, causing a NameError.
class User(Model):
username = CharField()
favorite_tweet = ForeignKeyField(Tweet, null=True) # NameError!!
class Tweet(Model):
message = TextField()
user = ForeignKeyField(User, backref='tweets')
One option is to simply use an IntegerField to store the raw ID:
class User(Model):
username = CharField()
favorite_tweet_id = IntegerField(null=True)
By using DeferredForeignKey we can get around the problem and still use a foreign key field:
class User(Model):
username = CharField()
# Tweet has not been defined yet so use the deferred reference.
favorite_tweet = DeferredForeignKey('Tweet', null=True)
class Tweet(Model):
message = TextField()
user = ForeignKeyField(User, backref='tweets')
# Now that Tweet is defined, "favorite_tweet" has been converted into
# a ForeignKeyField.
print(User.favorite_tweet)
# <ForeignKeyField: "user"."favorite_tweet">
There is one more quirk to watch out for, though. When you call create_table we will again encounter the
same issue. For this reason peewee will not automatically create a foreign key constraint for any
deferred foreign keys.
To create the tables and the foreign-key constraint, you can use the SchemaManager.create_foreign_key()
method to create the constraint after creating the tables:
# Will create the User and Tweet tables, but does *not* create a
# foreign-key constraint on User.favorite_tweet.
db.create_tables([User, Tweet])
# Create the foreign-key constraint:
User._schema.create_foreign_key(User.favorite_tweet)
NOTE:
Because SQLite has limited support for altering tables, foreign-key constraints cannot be added to a
table after it has been created.
Querying
This section will cover the basic CRUD operations commonly performed on a relational database:
• Model.create(), for executing INSERT queries.
• Model.save() and Model.update(), for executing UPDATE queries.
• Model.delete_instance() and Model.delete(), for executing DELETE queries.
• Model.select(), for executing SELECT queries.
NOTE:
There is also a large collection of example queries taken from the Postgresql Exercises website.
Examples are listed on the query examples document.
Creating a new record
You can use Model.create() to create a new model instance. This method accepts keyword arguments, where
the keys correspond to the names of the model's fields. A new instance is returned and a row is added to
the table.
>>> User.create(username='Charlie')
<__main__.User object at 0x2529350>
This will INSERT a new row into the database. The primary key will automatically be retrieved and stored
on the model instance.
Alternatively, you can build up a model instance programmatically and then call save():
>>> user = User(username='Charlie')
>>> user.save() # save() returns the number of rows modified.
1
>>> user.id
1
>>> huey = User()
>>> huey.username = 'Huey'
>>> huey.save()
1
>>> huey.id
2
When a model has a foreign key, you can directly assign a model instance to the foreign key field when
creating a new record.
>>> tweet = Tweet.create(user=huey, message='Hello!')
You can also use the value of the related object's primary key:
>>> tweet = Tweet.create(user=2, message='Hello again!')
If you simply wish to insert data and do not need to create a model instance, you can use Model.insert():
>>> User.insert(username='Mickey').execute()
3
After executing the insert query, the primary key of the new row is returned.
NOTE:
There are several ways you can speed up bulk insert operations. Check out the Bulk inserts recipe
section for more information.
Bulk inserts
There are a couple of ways you can load lots of data quickly. The naive approach is to simply call
Model.create() in a loop:
data_source = [
{'field1': 'val1-1', 'field2': 'val1-2'},
{'field1': 'val2-1', 'field2': 'val2-2'},
# ...
]
for data_dict in data_source:
MyModel.create(**data_dict)
The above approach is slow for a couple of reasons:
1. If you are not wrapping the loop in a transaction then each call to create() happens in its own
transaction. That is going to be really slow!
2. There is a decent amount of Python logic getting in your way, and each InsertQuery must be generated
and parsed into SQL.
3. That's a lot of data (in terms of raw bytes of SQL) you are sending to your database to parse.
4. We are retrieving the last insert id, which causes an additional query to be executed in some cases.
You can get a significant speedup by simply wrapping this in a transaction with atomic().
# This is much faster.
with db.atomic():
for data_dict in data_source:
MyModel.create(**data_dict)
The above code still suffers from points 2, 3 and 4. We can get another big boost by using insert_many().
This method accepts a list of tuples or dictionaries, and inserts multiple rows in a single query:
data_source = [
{'field1': 'val1-1', 'field2': 'val1-2'},
{'field1': 'val2-1', 'field2': 'val2-2'},
# ...
]
# Fastest way to INSERT multiple rows.
MyModel.insert_many(data_source).execute()
The insert_many() method also accepts a list of row-tuples, provided you also specify the corresponding
fields:
# We can INSERT tuples as well...
data = [('val1-1', 'val1-2'),
('val2-1', 'val2-2'),
('val3-1', 'val3-2')]
# But we need to indicate which fields the values correspond to.
MyModel.insert_many(data, fields=[MyModel.field1, MyModel.field2]).execute()
It is also a good practice to wrap the bulk insert in a transaction:
# You can, of course, wrap this in a transaction as well:
with db.atomic():
MyModel.insert_many(data, fields=fields).execute()
NOTE:
SQLite users should be aware of some caveats when using bulk inserts. Specifically, your SQLite3
version must be 3.7.11.0 or newer to take advantage of the bulk insert API. Additionally, by default
SQLite limits the number of bound variables in a SQL query to 999.
Inserting rows in batches
Depending on the number of rows in your data source, you may need to break it up into chunks. SQLite in
particular typically has a limit of 999 variables-per-query (batch size would then be roughly 1000 / row
length).
You can write a loop to batch your data into chunks (in which case it is strongly recommended you use a
transaction):
# Insert rows 100 at a time.
with db.atomic():
for idx in range(0, len(data_source), 100):
MyModel.insert_many(data_source[idx:idx+100]).execute()
Peewee comes with a chunked() helper function which you can use for efficiently chunking a generic
iterable into a series of batch-sized iterables:
from peewee import chunked
# Insert rows 100 at a time.
with db.atomic():
for batch in chunked(data_source, 100):
MyModel.insert_many(batch).execute()
Alternatives
The Model.bulk_create() method behaves much like Model.insert_many(), but instead it accepts a list of
unsaved model instances to insert, and it optionally accepts a batch-size parameter. To use the
bulk_create() API:
# Read list of usernames from a file, for example.
with open('user_list.txt') as fh:
# Create a list of unsaved User instances.
users = [User(username=line.strip()) for line in fh.readlines()]
# Wrap the operation in a transaction and batch INSERT the users
# 100 at a time.
with db.atomic():
User.bulk_create(users, batch_size=100)
NOTE:
If you are using Postgresql (which supports the RETURNING clause), then the previously-unsaved model
instances will have their new primary key values automatically populated.
Alternatively, you can use the Database.batch_commit() helper to process chunks of rows inside
batch-sized transactions. This method also provides a workaround for databases besides Postgresql, when
the primary-key of the newly-created rows must be obtained.
# List of row data to insert.
row_data = [{'username': 'u1'}, {'username': 'u2'}, ...]
# Assume there are 789 items in row_data. The following code will result in
# 8 total transactions (7x100 rows + 1x89 rows).
for row in db.batch_commit(row_data, 100):
User.create(**row)
Bulk-loading from another table
If the data you would like to bulk load is stored in another table, you can also create INSERT queries
whose source is a SELECT query. Use the Model.insert_from() method:
res = (TweetArchive
.insert_from(
Tweet.select(Tweet.user, Tweet.message),
fields=[TweetArchive.user, TweetArchive.message])
.execute())
The above query is equivalent to the following SQL:
INSERT INTO "tweet_archive" ("user_id", "message")
SELECT "user_id", "message" FROM "tweet";
Updating existing records
Once a model instance has a primary key, any subsequent call to save() will result in an UPDATE rather
than another INSERT. The model's primary key will not change:
>>> user.save() # save() returns the number of rows modified.
1
>>> user.id
1
>>> user.save()
>>> user.id
1
>>> huey.save()
1
>>> huey.id
2
If you want to update multiple records, issue an UPDATE query. The following example will update all
Tweet objects, marking them as published, if they were created before today. Model.update() accepts
keyword arguments where the keys correspond to the model's field names:
>>> today = datetime.today()
>>> query = Tweet.update(is_published=True).where(Tweet.creation_date < today)
>>> query.execute() # Returns the number of rows that were updated.
4
For more information, see the documentation on Model.update() and Update.
NOTE:
If you would like more information on performing atomic updates (such as incrementing the value of a
column), check out the atomic update recipes.
Atomic updates
Peewee allows you to perform atomic updates. Let's suppose we need to update some counters. The naive
approach would be to write something like this:
>>> for stat in Stat.select().where(Stat.url == request.url):
... stat.counter += 1
... stat.save()
Do not do this! Not only is this slow, but it is also vulnerable to race conditions if multiple processes
are updating the counter at the same time.
Instead, you can update the counters atomically using update():
>>> query = Stat.update(counter=Stat.counter + 1).where(Stat.url == request.url)
>>> query.execute()
You can make these update statements as complex as you like. Let's give all our employees a bonus equal
to their previous bonus plus 10% of their salary:
>>> query = Employee.update(bonus=(Employee.bonus + (Employee.salary * .1)))
>>> query.execute() # Give everyone a bonus!
We can even use a subquery to update the value of a column. Suppose we had a denormalized column on the
User model that stored the number of tweets a user had made, and we updated this value periodically. Here
is how you might write such a query:
>>> subquery = Tweet.select(fn.COUNT(Tweet.id)).where(Tweet.user == User.id)
>>> update = User.update(num_tweets=subquery)
>>> update.execute()
Upsert
Peewee provides support for varying types of upsert functionality. With SQLite prior to 3.24.0 and MySQL,
Peewee offers the replace(), which allows you to insert a record or, in the event of a constraint
violation, replace the existing record.
Example of using replace() and on_conflict_replace():
class User(Model):
username = TextField(unique=True)
last_login = DateTimeField(null=True)
# Insert or update the user. The "last_login" value will be updated
# regardless of whether the user existed previously.
user_id = (User
.replace(username='the-user', last_login=datetime.now())
.execute())
# This query is equivalent:
user_id = (User
.insert(username='the-user', last_login=datetime.now())
.on_conflict_replace()
.execute())
NOTE:
In addition to replace, SQLite, MySQL and Postgresql provide an ignore action (see:
on_conflict_ignore()) if you simply wish to insert and ignore any potential constraint violation.
MySQL supports upsert via the ON DUPLICATE KEY UPDATE clause. For example:
class User(Model):
username = TextField(unique=True)
last_login = DateTimeField(null=True)
login_count = IntegerField()
# Insert a new user.
User.create(username='huey', login_count=0)
# Simulate the user logging in. The login count and timestamp will be
# either created or updated correctly.
now = datetime.now()
rowid = (User
.insert(username='huey', last_login=now, login_count=1)
.on_conflict(
preserve=[User.last_login], # Use the value we would have inserted.
update={User.login_count: User.login_count + 1})
.execute())
In the above example, we could safely invoke the upsert query as many times as we wanted. The login count
will be incremented atomically, the last login column will be updated, and no duplicate rows will be
created.
Postgresql and SQLite (3.24.0 and newer) provide a different syntax that allows for more granular control
over which constraint violation should trigger the conflict resolution, and what values should be updated
or preserved.
Example of using on_conflict() to perform a Postgresql-style upsert (or SQLite 3.24+):
class User(Model):
username = TextField(unique=True)
last_login = DateTimeField(null=True)
login_count = IntegerField()
# Insert a new user.
User.create(username='huey', login_count=0)
# Simulate the user logging in. The login count and timestamp will be
# either created or updated correctly.
now = datetime.now()
rowid = (User
.insert(username='huey', last_login=now, login_count=1)
.on_conflict(
conflict_target=[User.username], # Which constraint?
preserve=[User.last_login], # Use the value we would have inserted.
update={User.login_count: User.login_count + 1})
.execute())
In the above example, we could safely invoke the upsert query as many times as we wanted. The login count
will be incremented atomically, the last login column will be updated, and no duplicate rows will be
created.
NOTE:
The main difference between MySQL and Postgresql/SQLite is that Postgresql and SQLite require that you
specify a conflict_target.
For more information, see Insert.on_conflict() and OnConflict.
Deleting records
To delete a single model instance, you can use the Model.delete_instance() shortcut. delete_instance()
will delete the given model instance and can optionally delete any dependent objects recursively (by
specifying recursive=True).
>>> user = User.get(User.id == 1)
>>> user.delete_instance() # Returns the number of rows deleted.
1
>>> User.get(User.id == 1)
UserDoesNotExist: instance matching query does not exist:
SQL: SELECT t1."id", t1."username" FROM "user" AS t1 WHERE t1."id" = ?
PARAMS: [1]
To delete an arbitrary set of rows, you can issue a DELETE query. The following will delete all Tweet
objects that are over one year old:
>>> query = Tweet.delete().where(Tweet.creation_date < one_year_ago)
>>> query.execute() # Returns the number of rows deleted.
7
For more information, see the documentation on:
• Model.delete_instance()
• Model.delete()
• DeleteQuery
Selecting a single record
You can use the Model.get() method to retrieve a single instance matching the given query. For
primary-key lookups, you can also use the shortcut method Model.get_by_id().
This method is a shortcut that calls Model.select() with the given query, but limits the result set to a
single row. Additionally, if no model matches the given query, a DoesNotExist exception will be raised.
>>> User.get(User.id == 1)
<__main__.User object at 0x25294d0>
>>> User.get_by_id(1) # Same as above.
<__main__.User object at 0x252df10>
>>> User[1] # Also same as above.
<__main__.User object at 0x252dd10>
>>> User.get(User.id == 1).username
u'Charlie'
>>> User.get(User.username == 'Charlie')
<__main__.User object at 0x2529410>
>>> User.get(User.username == 'nobody')
UserDoesNotExist: instance matching query does not exist:
SQL: SELECT t1."id", t1."username" FROM "user" AS t1 WHERE t1."username" = ?
PARAMS: ['nobody']
For more advanced operations, you can use SelectBase.get(). The following query retrieves the latest
tweet from the user named charlie:
>>> (Tweet
... .select()
... .join(User)
... .where(User.username == 'charlie')
... .order_by(Tweet.created_date.desc())
... .get())
<__main__.Tweet object at 0x2623410>
For more information, see the documentation on:
• Model.get()
• Model.get_by_id()
• Model.get_or_none() - if no matching row is found, return None.
• Model.first()
• Model.select()
• SelectBase.get()
Create or get
Peewee has one helper method for performing "get/create" type operations: Model.get_or_create(), which
first attempts to retrieve the matching row. Failing that, a new row will be created.
For "create or get" type logic, typically one would rely on a unique constraint or primary key to prevent
the creation of duplicate objects. As an example, let's say we wish to implement registering a new user
account using the example User model. The User model has a unique constraint on the username field, so we
will rely on the database's integrity guarantees to ensure we don't end up with duplicate usernames:
try:
with db.atomic():
return User.create(username=username)
except peewee.IntegrityError:
# `username` is a unique column, so this username already exists,
# making it safe to call .get().
return User.get(User.username == username)
You can easily encapsulate this type of logic as a classmethod on your own Model classes.
The above example first attempts at creation, then falls back to retrieval, relying on the database to
enforce a unique constraint. If you prefer to attempt to retrieve the record first, you can use
get_or_create(). This method is implemented along the same lines as the Django function of the same name.
You can use the Django-style keyword argument filters to specify your WHERE conditions. The function
returns a 2-tuple containing the instance and a boolean value indicating if the object was created.
Here is how you might implement user account creation using get_or_create():
user, created = User.get_or_create(username=username)
Suppose we have a different model Person and would like to get or create a person object. The only
conditions we care about when retrieving the Person are their first and last names, but if we end up
needing to create a new record, we will also specify their date-of-birth and favorite color:
person, created = Person.get_or_create(
first_name=first_name,
last_name=last_name,
defaults={'dob': dob, 'favorite_color': 'green'})
Any keyword argument passed to get_or_create() will be used in the get() portion of the logic, except for
the defaults dictionary, which will be used to populate values on newly-created instances.
For more details read the documentation for Model.get_or_create().
Selecting multiple records
We can use Model.select() to retrieve rows from the table. When you construct a SELECT query, the
database will return any rows that correspond to your query. Peewee allows you to iterate over these
rows, as well as use indexing and slicing operations:
>>> query = User.select()
>>> [user.username for user in query]
['Charlie', 'Huey', 'Peewee']
>>> query[1]
<__main__.User at 0x7f83e80f5550>
>>> query[1].username
'Huey'
>>> query[:2]
[<__main__.User at 0x7f83e80f53a8>, <__main__.User at 0x7f83e80f5550>]
Select queries are smart, in that you can iterate, index and slice the query multiple times but the query
is only executed once.
In the following example, we will simply call select() and iterate over the return value, which is an
instance of Select. This will return all the rows in the User table:
>>> for user in User.select():
... print user.username
...
Charlie
Huey
Peewee
NOTE:
Subsequent iterations of the same query will not hit the database as the results are cached. To
disable this behavior (to reduce memory usage), call Select.iterator() when iterating.
When iterating over a model that contains a foreign key, be careful with the way you access values on
related models. Accidentally resolving a foreign key or iterating over a back-reference can cause N+1
query behavior.
When you create a foreign key, such as Tweet.user, you can use the backref to create a back-reference
(User.tweets). Back-references are exposed as Select instances:
>>> tweet = Tweet.get()
>>> tweet.user # Accessing a foreign key returns the related model.
<tw.User at 0x7f3ceb017f50>
>>> user = User.get()
>>> user.tweets # Accessing a back-reference returns a query.
<peewee.ModelSelect at 0x7f73db3bafd0>
You can iterate over the user.tweets back-reference just like any other Select:
>>> for tweet in user.tweets:
... print(tweet.message)
...
hello world
this is fun
look at this picture of my food
In addition to returning model instances, Select queries can return dictionaries, tuples and namedtuples.
Depending on your use-case, you may find it easier to work with rows as dictionaries, for example:
>>> query = User.select().dicts()
>>> for row in query:
... print(row)
{'id': 1, 'username': 'Charlie'}
{'id': 2, 'username': 'Huey'}
{'id': 3, 'username': 'Peewee'}
See namedtuples(), tuples(), dicts() for more information.
Iterating over large result-sets
By default peewee will cache the rows returned when iterating over a Select query. This is an
optimization to allow multiple iterations as well as indexing and slicing without causing additional
queries. This caching can problematic, however, when you plan to iterate over a large number of rows.
To reduce the amount of memory used by peewee when iterating over a query, use the iterator() method.
This method allows you to iterate without caching each model returned, using much less memory when
iterating over large result sets.
# Let's assume we've got 10 million stat objects to dump to a csv file.
stats = Stat.select()
# Our imaginary serializer class
serializer = CSVSerializer()
# Loop over all the stats and serialize.
for stat in stats.iterator():
serializer.serialize_object(stat)
For simple queries you can see further speed improvements by returning rows as dictionaries, namedtuples
or tuples. The following methods can be used on any Select query to change the result row type:
• dicts()
• namedtuples()
• tuples()
When iterating over a large number of rows that contain columns from multiple tables, peewee will
reconstruct the model graph for each row returned. This operation can be slow for complex graphs. For
example, if we were selecting a list of tweets along with the username and avatar of the tweet's author,
Peewee would have to create two objects for each row (a tweet and a user). In addition to the above
row-types, there is a fourth method objects() which will return the rows as model instances, but will not
attempt to resolve the model graph.
For example:
query = (Tweet
.select(Tweet, User) # Select tweet and user data.
.join(User))
# Note that the user columns are stored in a separate User instance
# accessible at tweet.user:
for tweet in query:
print(tweet.user.username, tweet.content)
# Using ".objects()" will not create the tweet.user object and assigns all
# user attributes to the tweet instance:
for tweet in query.objects():
print(tweet.username, tweet.content)
For maximum performance, you can execute queries and then iterate over the results using the underlying
database cursor. Database.execute() accepts a query object, executes the query, and returns a DB-API 2.0
Cursor object. The cursor will return the raw row-tuples:
query = Tweet.select(Tweet.content, User.username).join(User)
cursor = database.execute(query)
for (content, username) in cursor:
print(username, '->', content)
Filtering records
You can filter for particular records using normal python operators. Peewee supports a wide variety of
query operators.
>>> user = User.get(User.username == 'Charlie')
>>> for tweet in Tweet.select().where(Tweet.user == user, Tweet.is_published == True):
... print(tweet.user.username, '->', tweet.message)
...
Charlie -> hello world
Charlie -> this is fun
>>> for tweet in Tweet.select().where(Tweet.created_date < datetime.datetime(2011, 1, 1)):
... print(tweet.message, tweet.created_date)
...
Really old tweet 2010-01-01 00:00:00
You can also filter across joins:
>>> for tweet in Tweet.select().join(User).where(User.username == 'Charlie'):
... print(tweet.message)
hello world
this is fun
look at this picture of my food
If you want to express a complex query, use parentheses and python's bitwise or and and operators:
>>> Tweet.select().join(User).where(
... (User.username == 'Charlie') |
... (User.username == 'Peewee Herman'))
NOTE:
Note that Peewee uses bitwise operators (& and |) rather than logical operators (and and or). The
reason for this is that Python coerces the return value of logical operations to a boolean value. This
is also the reason why "IN" queries must be expressed using .in_() rather than the in operator.
Check out the table of query operations to see what types of queries are possible.
NOTE:
A lot of fun things can go in the where clause of a query, such as:
• A field expression, e.g. User.username == 'Charlie'
• A function expression, e.g. fn.Lower(fn.Substr(User.username, 1, 1)) == 'a'
• A comparison of one column to another, e.g. Employee.salary < (Employee.tenure * 1000) + 40000
You can also nest queries, for example tweets by users whose username starts with "a":
# get users whose username starts with "a"
a_users = User.select().where(fn.Lower(fn.Substr(User.username, 1, 1)) == 'a')
# the ".in_()" method signifies an "IN" query
a_user_tweets = Tweet.select().where(Tweet.user.in_(a_users))
More query examples
NOTE:
For a wide range of example queries, see the Query Examples document, which shows how to implements
queries from the PostgreSQL Exercises website.
Get active users:
User.select().where(User.active == True)
Get users who are either staff or superusers:
User.select().where(
(User.is_staff == True) | (User.is_superuser == True))
Get tweets by user named "charlie":
Tweet.select().join(User).where(User.username == 'charlie')
Get tweets by staff or superusers (assumes FK relationship):
Tweet.select().join(User).where(
(User.is_staff == True) | (User.is_superuser == True))
Get tweets by staff or superusers using a subquery:
staff_super = User.select(User.id).where(
(User.is_staff == True) | (User.is_superuser == True))
Tweet.select().where(Tweet.user.in_(staff_super))
Sorting records
To return rows in order, use the order_by() method:
>>> for t in Tweet.select().order_by(Tweet.created_date):
... print(t.pub_date)
...
2010-01-01 00:00:00
2011-06-07 14:08:48
2011-06-07 14:12:57
>>> for t in Tweet.select().order_by(Tweet.created_date.desc()):
... print(t.pub_date)
...
2011-06-07 14:12:57
2011-06-07 14:08:48
2010-01-01 00:00:00
You can also use + and - prefix operators to indicate ordering:
# The following queries are equivalent:
Tweet.select().order_by(Tweet.created_date.desc())
Tweet.select().order_by(-Tweet.created_date) # Note the "-" prefix.
# Similarly you can use "+" to indicate ascending order, though ascending
# is the default when no ordering is otherwise specified.
User.select().order_by(+User.username)
You can also order across joins. Assuming you want to order tweets by the username of the author, then by
created_date:
query = (Tweet
.select()
.join(User)
.order_by(User.username, Tweet.created_date.desc()))
SELECT t1."id", t1."user_id", t1."message", t1."is_published", t1."created_date"
FROM "tweet" AS t1
INNER JOIN "user" AS t2
ON t1."user_id" = t2."id"
ORDER BY t2."username", t1."created_date" DESC
When sorting on a calculated value, you can either include the necessary SQL expressions, or reference
the alias assigned to the value. Here are two examples illustrating these methods:
# Let's start with our base query. We want to get all usernames and the number of
# tweets they've made. We wish to sort this list from users with most tweets to
# users with fewest tweets.
query = (User
.select(User.username, fn.COUNT(Tweet.id).alias('num_tweets'))
.join(Tweet, JOIN.LEFT_OUTER)
.group_by(User.username))
You can order using the same COUNT expression used in the select clause. In the example below we are
ordering by the COUNT() of tweet ids descending:
query = (User
.select(User.username, fn.COUNT(Tweet.id).alias('num_tweets'))
.join(Tweet, JOIN.LEFT_OUTER)
.group_by(User.username)
.order_by(fn.COUNT(Tweet.id).desc()))
Alternatively, you can reference the alias assigned to the calculated value in the select clause. This
method has the benefit of being a bit easier to read. Note that we are not referring to the named alias
directly, but are wrapping it using the SQL helper:
query = (User
.select(User.username, fn.COUNT(Tweet.id).alias('num_tweets'))
.join(Tweet, JOIN.LEFT_OUTER)
.group_by(User.username)
.order_by(SQL('num_tweets').desc()))
Or, to do things the "peewee" way:
ntweets = fn.COUNT(Tweet.id)
query = (User
.select(User.username, ntweets.alias('num_tweets'))
.join(Tweet, JOIN.LEFT_OUTER)
.group_by(User.username)
.order_by(ntweets.desc())
Getting random records
Occasionally you may want to pull a random record from the database. You can accomplish this by ordering
by the random or rand function (depending on your database):
Postgresql and Sqlite use the Random function:
# Pick 5 lucky winners:
LotteryNumber.select().order_by(fn.Random()).limit(5)
MySQL uses Rand:
# Pick 5 lucky winners:
LotterNumber.select().order_by(fn.Rand()).limit(5)
Paginating records
The paginate() method makes it easy to grab a page or records. paginate() takes two parameters,
page_number, and items_per_page.
ATTENTION:
Page numbers are 1-based, so the first page of results will be page 1.
>>> for tweet in Tweet.select().order_by(Tweet.id).paginate(2, 10):
... print(tweet.message)
...
tweet 10
tweet 11
tweet 12
tweet 13
tweet 14
tweet 15
tweet 16
tweet 17
tweet 18
tweet 19
If you would like more granular control, you can always use limit() and offset().
Counting records
You can count the number of rows in any select query:
>>> Tweet.select().count()
100
>>> Tweet.select().where(Tweet.id > 50).count()
50
Peewee will wrap your query in an outer query that performs a count, which results in SQL like:
SELECT COUNT(1) FROM ( ... your query ... );
Aggregating records
Suppose you have some users and want to get a list of them along with the count of tweets in each.
query = (User
.select(User, fn.Count(Tweet.id).alias('count'))
.join(Tweet, JOIN.LEFT_OUTER)
.group_by(User))
The resulting query will return User objects with all their normal attributes plus an additional
attribute count which will contain the count of tweets for each user. We use a left outer join to include
users who have no tweets.
Let's assume you have a tagging application and want to find tags that have a certain number of related
objects. For this example we'll use some different models in a many-to-many configuration:
class Photo(Model):
image = CharField()
class Tag(Model):
name = CharField()
class PhotoTag(Model):
photo = ForeignKeyField(Photo)
tag = ForeignKeyField(Tag)
Now say we want to find tags that have at least 5 photos associated with them:
query = (Tag
.select()
.join(PhotoTag)
.join(Photo)
.group_by(Tag)
.having(fn.Count(Photo.id) > 5))
This query is equivalent to the following SQL:
SELECT t1."id", t1."name"
FROM "tag" AS t1
INNER JOIN "phototag" AS t2 ON t1."id" = t2."tag_id"
INNER JOIN "photo" AS t3 ON t2."photo_id" = t3."id"
GROUP BY t1."id", t1."name"
HAVING Count(t3."id") > 5
Suppose we want to grab the associated count and store it on the tag:
query = (Tag
.select(Tag, fn.Count(Photo.id).alias('count'))
.join(PhotoTag)
.join(Photo)
.group_by(Tag)
.having(fn.Count(Photo.id) > 5))
Retrieving Scalar Values
You can retrieve scalar values by calling Query.scalar(). For instance:
>>> PageView.select(fn.Count(fn.Distinct(PageView.url))).scalar()
100
You can retrieve multiple scalar values by passing as_tuple=True:
>>> Employee.select(
... fn.Min(Employee.salary), fn.Max(Employee.salary)
... ).scalar(as_tuple=True)
(30000, 50000)
Window functions
A Window function refers to an aggregate function that operates on a sliding window of data that is being
processed as part of a SELECT query. Window functions make it possible to do things like:
1. Perform aggregations against subsets of a result-set.
2. Calculate a running total.
3. Rank results.
4. Compare a row value to a value in the preceding (or succeeding!) row(s).
peewee comes with support for SQL window functions, which can be created by calling Function.over() and
passing in your partitioning or ordering parameters.
For the following examples, we'll use the following model and sample data:
class Sample(Model):
counter = IntegerField()
value = FloatField()
data = [(1, 10),
(1, 20),
(2, 1),
(2, 3),
(3, 100)]
Sample.insert_many(data, fields=[Sample.counter, Sample.value]).execute()
Our sample table now contains:
┌───┬─────────┬───────┐
│id │ counter │ value │
├───┼─────────┼───────┤
│1 │ 1 │ 10.0 │
├───┼─────────┼───────┤
│2 │ 1 │ 20.0 │
├───┼─────────┼───────┤
│3 │ 2 │ 1.0 │
├───┼─────────┼───────┤
│4 │ 2 │ 3.0 │
├───┼─────────┼───────┤
│5 │ 3 │ 100.0 │
└───┴─────────┴───────┘
Ordered Windows
Let's calculate a running sum of the value field. In order for it to be a "running" sum, we need it to be
ordered, so we'll order with respect to the Sample's id field:
query = Sample.select(
Sample.counter,
Sample.value,
fn.SUM(Sample.value).over(order_by=[Sample.id]).alias('total'))
for sample in query:
print(sample.counter, sample.value, sample.total)
# 1 10. 10.
# 1 20. 30.
# 2 1. 31.
# 2 3. 34.
# 3 100 134.
For another example, we'll calculate the difference between the current value and the previous value,
when ordered by the id:
difference = Sample.value - fn.LAG(Sample.value, 1).over(order_by=[Sample.id])
query = Sample.select(
Sample.counter,
Sample.value,
difference.alias('diff'))
for sample in query:
print(sample.counter, sample.value, sample.diff)
# 1 10. NULL
# 1 20. 10. -- (20 - 10)
# 2 1. -19. -- (1 - 20)
# 2 3. 2. -- (3 - 1)
# 3 100 97. -- (100 - 3)
Partitioned Windows
Let's calculate the average value for each distinct "counter" value. Notice that there are three possible
values for the counter field (1, 2, and 3). We can do this by calculating the AVG() of the value column
over a window that is partitioned depending on the counter field:
query = Sample.select(
Sample.counter,
Sample.value,
fn.AVG(Sample.value).over(partition_by=[Sample.counter]).alias('cavg'))
for sample in query:
print(sample.counter, sample.value, sample.cavg)
# 1 10. 15.
# 1 20. 15.
# 2 1. 2.
# 2 3. 2.
# 3 100 100.
We can use ordering within partitions by specifying both the order_by and partition_by parameters. For an
example, let's rank the samples by value within each distinct counter group.
query = Sample.select(
Sample.counter,
Sample.value,
fn.RANK().over(
order_by=[Sample.value],
partition_by=[Sample.counter]).alias('rank'))
for sample in query:
print(sample.counter, sample.value, sample.rank)
# 1 10. 1
# 1 20. 2
# 2 1. 1
# 2 3. 2
# 3 100 1
Bounded windows
By default, window functions are evaluated using an unbounded preceding start for the window, and the
current row as the end. We can change the bounds of the window our aggregate functions operate on by
specifying a start and/or end in the call to Function.over(). Additionally, Peewee comes with
helper-methods on the Window object for generating the appropriate boundary references:
• Window.CURRENT_ROW - attribute that references the current row.
• Window.preceding() - specify number of row(s) preceding, or omit number to indicate all preceding rows.
• Window.following() - specify number of row(s) following, or omit number to indicate all following rows.
To examine how boundaries work, we'll calculate a running total of the value column, ordered with respect
to id, but we'll only look the running total of the current row and it's two preceding rows:
query = Sample.select(
Sample.counter,
Sample.value,
fn.SUM(Sample.value).over(
order_by=[Sample.id],
start=Window.preceding(2),
end=Window.CURRENT_ROW).alias('rsum'))
for sample in query:
print(sample.counter, sample.value, sample.rsum)
# 1 10. 10.
# 1 20. 30. -- (20 + 10)
# 2 1. 31. -- (1 + 20 + 10)
# 2 3. 24. -- (3 + 1 + 20)
# 3 100 104. -- (100 + 3 + 1)
NOTE:
Technically we did not need to specify the end=Window.CURRENT because that is the default. It was
shown in the example for demonstration.
Let's look at another example. In this example we will calculate the "opposite" of a running total, in
which the total sum of all values is decreased by the value of the samples, ordered by id. To accomplish
this, we'll calculate the sum from the current row to the last row.
query = Sample.select(
Sample.counter,
Sample.value,
fn.SUM(Sample.value).over(
order_by=[Sample.id],
start=Window.CURRENT_ROW,
end=Window.following()).alias('rsum'))
# 1 10. 134. -- (10 + 20 + 1 + 3 + 100)
# 1 20. 124. -- (20 + 1 + 3 + 100)
# 2 1. 104. -- (1 + 3 + 100)
# 2 3. 103. -- (3 + 100)
# 3 100 100. -- (100)
Filtered Aggregates
Aggregate functions may also support filter functions (Postgres and Sqlite 3.25+), which get translated
into a FILTER (WHERE...) clause. Filter expressions are added to an aggregate function with the
Function.filter() method.
For an example, we will calculate the running sum of the value field with respect to the id, but we will
filter-out any samples whose counter=2.
query = Sample.select(
Sample.counter,
Sample.value,
fn.SUM(Sample.value).filter(Sample.counter != 2).over(
order_by=[Sample.id]).alias('csum'))
for sample in query:
print(sample.counter, sample.value, sample.csum)
# 1 10. 10.
# 1 20. 30.
# 2 1. 30.
# 2 3. 30.
# 3 100 130.
NOTE:
The call to filter() must precede the call to over().
Reusing Window Definitions
If you intend to use the same window definition for multiple aggregates, you can create a Window object.
The Window object takes the same parameters as Function.over(), and can be passed to the over() method
in-place of the individual parameters.
Here we'll declare a single window, ordered with respect to the sample id, and call several window
functions using that window definition:
win = Window(order_by=[Sample.id])
query = Sample.select(
Sample.counter,
Sample.value,
fn.LEAD(Sample.value).over(win),
fn.LAG(Sample.value).over(win),
fn.SUM(Sample.value).over(win)
).window(win) # Include our window definition in query.
for row in query.tuples():
print(row)
# counter value lead() lag() sum()
# 1 10. 20. NULL 10.
# 1 20. 1. 10. 30.
# 2 1. 3. 20. 31.
# 2 3. 100. 1. 34.
# 3 100. NULL 3. 134.
Multiple window definitions
In the previous example, we saw how to declare a Window definition and re-use it for multiple different
aggregations. You can include as many window definitions as you need in your queries, but it is necessary
to ensure each window has a unique alias:
w1 = Window(order_by=[Sample.id]).alias('w1')
w2 = Window(partition_by=[Sample.counter]).alias('w2')
query = Sample.select(
Sample.counter,
Sample.value,
fn.SUM(Sample.value).over(w1).alias('rsum'), # Running total.
fn.AVG(Sample.value).over(w2).alias('cavg') # Avg per category.
).window(w1, w2) # Include our window definitions.
for sample in query:
print(sample.counter, sample.value, sample.rsum, sample.cavg)
# counter value rsum cavg
# 1 10. 10. 15.
# 1 20. 30. 15.
# 2 1. 31. 2.
# 2 3. 34. 2.
# 3 100 134. 100.
Frame types: RANGE vs ROWS
Depending on the frame type, the database will process ordered groups differently. Let's create two
additional Sample rows to visualize the difference:
>>> Sample.create(counter=1, value=20.)
<Sample 6>
>>> Sample.create(counter=2, value=1.)
<Sample 7>
Our table now contains:
┌───┬─────────┬───────┐
│id │ counter │ value │
├───┼─────────┼───────┤
│1 │ 1 │ 10.0 │
├───┼─────────┼───────┤
│2 │ 1 │ 20.0 │
├───┼─────────┼───────┤
│3 │ 2 │ 1.0 │
├───┼─────────┼───────┤
│4 │ 2 │ 3.0 │
├───┼─────────┼───────┤
│5 │ 3 │ 100.0 │
├───┼─────────┼───────┤
│6 │ 1 │ 20.0 │
├───┼─────────┼───────┤
│7 │ 2 │ 1.0 │
└───┴─────────┴───────┘
Let's examine the difference by calculating a "running sum" of the samples, ordered with respect to the
counter and value fields. To specify the frame type, we can use either:
• Window.RANGE
• Window.ROWS
The behavior of RANGE, when there are logical duplicates, may lead to unexpected results:
query = Sample.select(
Sample.counter,
Sample.value,
fn.SUM(Sample.value).over(
order_by=[Sample.counter, Sample.value],
frame_type=Window.RANGE).alias('rsum'))
for sample in query.order_by(Sample.counter, Sample.value):
print(sample.counter, sample.value, sample.rsum)
# counter value rsum
# 1 10. 10.
# 1 20. 50.
# 1 20. 50.
# 2 1. 52.
# 2 1. 52.
# 2 3. 55.
# 3 100 155.
With the inclusion of the new rows we now have some rows that have duplicate category and value values.
The RANGE frame type causes these duplicates to be evaluated together rather than separately.
The more expected result can be achieved by using ROWS as the frame-type:
query = Sample.select(
Sample.counter,
Sample.value,
fn.SUM(Sample.value).over(
order_by=[Sample.counter, Sample.value],
frame_type=Window.ROWS).alias('rsum'))
for sample in query.order_by(Sample.counter, Sample.value):
print(sample.counter, sample.value, sample.rsum)
# counter value rsum
# 1 10. 10.
# 1 20. 30.
# 1 20. 50.
# 2 1. 51.
# 2 1. 52.
# 2 3. 55.
# 3 100 155.
Peewee uses these rules for determining what frame-type to use:
• If the user specifies a frame_type, that frame type will be used.
• If start and/or end boundaries are specified Peewee will default to using ROWS.
• If the user did not specify frame type or start/end boundaries, Peewee will use the database default,
which is RANGE.
NOTE:
For information about the window function APIs, see:
• Function.over()
• Function.filter()
• Window
For general information on window functions, the postgresql docs. have a good overview.
Retrieving row tuples / dictionaries / namedtuples
Sometimes you do not need the overhead of creating model instances and simply want to iterate over the
row data without needing all the APIs provided Model. To do this, use:
• dicts()
• namedtuples()
• tuples()
• objects() -- accepts an arbitrary constructor function which is called with the row tuple.
stats = (Stat
.select(Stat.url, fn.Count(Stat.url))
.group_by(Stat.url)
.tuples())
# iterate over a list of 2-tuples containing the url and count
for stat_url, stat_count in stats:
print(stat_url, stat_count)
Similarly, you can return the rows from the cursor as dictionaries using dicts():
stats = (Stat
.select(Stat.url, fn.Count(Stat.url).alias('ct'))
.group_by(Stat.url)
.dicts())
# iterate over a list of 2-tuples containing the url and count
for stat in stats:
print(stat['url'], stat['ct'])
Returning Clause
PostgresqlDatabase supports a RETURNING clause on UPDATE, INSERT and DELETE queries. Specifying a
RETURNING clause allows you to iterate over the rows accessed by the query.
For example, let's say you have an Update that deactivates all user accounts whose registration has
expired. After deactivating them, you want to send each user an email letting them know their account was
deactivated. Rather than writing two queries, a SELECT and an UPDATE, you can do this in a single UPDATE
query with a RETURNING clause:
query = (User
.update(is_active=False)
.where(User.registration_expired == True)
.returning(User))
# Send an email to every user that was deactivated.
for deactivate_user in query.execute():
send_deactivation_email(deactivated_user)
The RETURNING clause is also available on Insert and Delete. When used with INSERT, the newly-created
rows will be returned. When used with DELETE, the deleted rows will be returned.
The only limitation of the RETURNING clause is that it can only consist of columns from tables listed in
the query's FROM clause. To select all columns from a particular table, you can simply pass in the Model
class.
Common Table Expressions
Peewee supports the inclusion of common table expressions (CTEs) in all types of queries. CTEs may be
useful for:
• Factoring out a common subquery.
• Grouping or filtering by a column derived in the CTE's result set.
• Writing recursive queries.
To declare a Select query for use as a CTE, use cte() method, which wraps the query in a CTE object. To
indicate that a CTE should be included as part of a query, use the Query.with_cte() method, passing a
list of CTE objects.
Simple Example
For an example, let's say we have some data points that consist of a key and a floating-point value.
Let's define our model and populate some test data:
class Sample(Model):
key = TextField()
value = FloatField()
data = (
('a', (1.25, 1.5, 1.75)),
('b', (2.1, 2.3, 2.5, 2.7, 2.9)),
('c', (3.5, 3.5)))
# Populate data.
for key, values in data:
Sample.insert_many([(key, value) for value in values],
fields=[Sample.key, Sample.value]).execute()
Let's use a CTE to calculate, for each distinct key, which values were above-average for that key.
# First we'll declare the query that will be used as a CTE. This query
# simply determines the average value for each key.
cte = (Sample
.select(Sample.key, fn.AVG(Sample.value).alias('avg_value'))
.group_by(Sample.key)
.cte('key_avgs', columns=('key', 'avg_value')))
# Now we'll query the sample table, using our CTE to find rows whose value
# exceeds the average for the given key. We'll calculate how far above the
# average the given sample's value is, as well.
query = (Sample
.select(Sample.key, Sample.value)
.join(cte, on=(Sample.key == cte.c.key))
.where(Sample.value > cte.c.avg_value)
.order_by(Sample.value)
.with_cte(cte))
We can iterate over the samples returned by the query to see which samples had above-average values for
their given group:
>>> for sample in query:
... print(sample.key, sample.value)
# 'a', 1.75
# 'b', 2.7
# 'b', 2.9
Complex Example
For a more complete example, let's consider the following query which uses multiple CTEs to find
per-product sales totals in only the top sales regions. Our model looks like this:
class Order(Model):
region = TextField()
amount = FloatField()
product = TextField()
quantity = IntegerField()
Here is how the query might be written in SQL. This example can be found in the postgresql documentation.
WITH regional_sales AS (
SELECT region, SUM(amount) AS total_sales
FROM orders
GROUP BY region
), top_regions AS (
SELECT region
FROM regional_sales
WHERE total_sales > (SELECT SUM(total_sales) / 10 FROM regional_sales)
)
SELECT region,
product,
SUM(quantity) AS product_units,
SUM(amount) AS product_sales
FROM orders
WHERE region IN (SELECT region FROM top_regions)
GROUP BY region, product;
With Peewee, we would write:
reg_sales = (Order
.select(Order.region,
fn.SUM(Order.amount).alias('total_sales'))
.group_by(Order.region)
.cte('regional_sales'))
top_regions = (reg_sales
.select(reg_sales.c.region)
.where(reg_sales.c.total_sales > (
reg_sales.select(fn.SUM(reg_sales.c.total_sales) / 10)))
.cte('top_regions'))
query = (Order
.select(Order.region,
Order.product,
fn.SUM(Order.quantity).alias('product_units'),
fn.SUM(Order.amount).alias('product_sales'))
.where(Order.region.in_(top_regions.select(top_regions.c.region)))
.group_by(Order.region, Order.product)
.with_cte(regional_sales, top_regions))
Recursive CTEs
Peewee supports recursive CTEs. Recursive CTEs can be useful when, for example, you have a tree
data-structure represented by a parent-link foreign key. Suppose, for example, that we have a hierarchy
of categories for an online bookstore. We wish to generate a table showing all categories and their
absolute depths, along with the path from the root to the category.
We'll assume the following model definition, in which each category has a foreign-key to its immediate
parent category:
class Category(Model):
name = TextField()
parent = ForeignKeyField('self', backref='children', null=True)
To list all categories along with their depth and parents, we can use a recursive CTE:
# Define the base case of our recursive CTE. This will be categories that
# have a null parent foreign-key.
Base = Category.alias()
level = Value(1).alias('level')
path = Base.name.alias('path')
base_case = (Base
.select(Base.name, Base.parent, level, path)
.where(Base.parent.is_null())
.cte('base', recursive=True))
# Define the recursive terms.
RTerm = Category.alias()
rlevel = (base_case.c.level + 1).alias('level')
rpath = base_case.c.path.concat('->').concat(RTerm.name).alias('path')
recursive = (RTerm
.select(RTerm.name, RTerm.parent, rlevel, rpath)
.join(base_case, on=(RTerm.parent == base_case.c.id)))
# The recursive CTE is created by taking the base case and UNION ALL with
# the recursive term.
cte = base_case.union_all(recursive)
# We will now query from the CTE to get the categories, their levels, and
# their paths.
query = (cte
.select_from(cte.c.name, cte.c.level, cte.c.path)
.order_by(cte.c.path))
# We can now iterate over a list of all categories and print their names,
# absolute levels, and path from root -> category.
for category in query:
print(category.name, category.level, category.path)
# Example output:
# root, 1, root
# p1, 2, root->p1
# c1-1, 3, root->p1->c1-1
# c1-2, 3, root->p1->c1-2
# p2, 2, root->p2
# c2-1, 3, root->p2->c2-1
Foreign Keys and Joins
This section have been moved into its own document: relationships.
Query operators
The following types of comparisons are supported by peewee:
┌───────────┬───────────────────────────────────────┐
│Comparison │ Meaning │
├───────────┼───────────────────────────────────────┤
│== │ x equals y │
├───────────┼───────────────────────────────────────┤
│< │ x is less than y │
├───────────┼───────────────────────────────────────┤
│<= │ x is less than or equal to y │
├───────────┼───────────────────────────────────────┤
│> │ x is greater than y │
├───────────┼───────────────────────────────────────┤
│>= │ x is greater than or equal to y │
├───────────┼───────────────────────────────────────┤
│!= │ x is not equal to y │
├───────────┼───────────────────────────────────────┤
│<< │ x IN y, where y is a list or query │
├───────────┼───────────────────────────────────────┤
│>> │ x IS y, where y is None/NULL │
├───────────┼───────────────────────────────────────┤
│% │ x LIKE y where y may contain │
│ │ wildcards │
├───────────┼───────────────────────────────────────┤
│** │ x ILIKE y where y may contain │
│ │ wildcards │
├───────────┼───────────────────────────────────────┤
│^ │ x XOR y │
├───────────┼───────────────────────────────────────┤
│~ │ Unary negation (e.g., NOT x) │
└───────────┴───────────────────────────────────────┘
Because I ran out of operators to override, there are some additional query operations available as
methods:
┌────────────────────┬───────────────────────────────────────┐
│Method │ Meaning │
└────────────────────┴───────────────────────────────────────┘
│.in_(value) │ IN lookup (identical to <<). │
├────────────────────┼───────────────────────────────────────┤
│.not_in(value) │ NOT IN lookup. │
├────────────────────┼───────────────────────────────────────┤
│.is_null(is_null) │ IS NULL or IS NOT NULL. Accepts │
│ │ boolean param. │
├────────────────────┼───────────────────────────────────────┤
│.contains(substr) │ Wild-card search for substring. │
├────────────────────┼───────────────────────────────────────┤
│.startswith(prefix) │ Search for values beginning with │
│ │ prefix. │
├────────────────────┼───────────────────────────────────────┤
│.endswith(suffix) │ Search for values ending with suffix. │
├────────────────────┼───────────────────────────────────────┤
│.between(low, high) │ Search for values between low and │
│ │ high. │
├────────────────────┼───────────────────────────────────────┤
│.regexp(exp) │ Regular expression match │
│ │ (case-sensitive). │
├────────────────────┼───────────────────────────────────────┤
│.iregexp(exp) │ Regular expression match │
│ │ (case-insensitive). │
├────────────────────┼───────────────────────────────────────┤
│.bin_and(value) │ Binary AND. │
├────────────────────┼───────────────────────────────────────┤
│.bin_or(value) │ Binary OR. │
├────────────────────┼───────────────────────────────────────┤
│.concat(other) │ Concatenate two strings or objects │
│ │ using ||. │
├────────────────────┼───────────────────────────────────────┤
│.distinct() │ Mark column for DISTINCT selection. │
├────────────────────┼───────────────────────────────────────┤
│.collate(collation) │ Specify column with the given │
│ │ collation. │
├────────────────────┼───────────────────────────────────────┤
│.cast(type) │ Cast the value of the column to the │
│ │ given type. │
└────────────────────┴───────────────────────────────────────┘
To combine clauses using logical operators, use:
┌─────────┬──────────────────────┬────────────────────────────────────┐
│Operator │ Meaning │ Example │
├─────────┼──────────────────────┼────────────────────────────────────┤
│& │ AND │ (User.is_active == True) & │
│ │ │ (User.is_admin == True) │
├─────────┼──────────────────────┼────────────────────────────────────┤
│| (pipe) │ OR │ (User.is_admin) | │
│ │ │ (User.is_superuser) │
├─────────┼──────────────────────┼────────────────────────────────────┤
│~ │ NOT (unary negation) │ ~(User.username.contains('admin')) │
└─────────┴──────────────────────┴────────────────────────────────────┘
Here is how you might use some of these query operators:
# Find the user whose username is "charlie".
User.select().where(User.username == 'charlie')
# Find the users whose username is in [charlie, huey, mickey]
User.select().where(User.username.in_(['charlie', 'huey', 'mickey']))
Employee.select().where(Employee.salary.between(50000, 60000))
Employee.select().where(Employee.name.startswith('C'))
Blog.select().where(Blog.title.contains(search_string))
Here is how you might combine expressions. Comparisons can be arbitrarily complex.
NOTE:
Note that the actual comparisons are wrapped in parentheses. Python's operator precedence necessitates
that comparisons be wrapped in parentheses.
# Find any users who are active administrations.
User.select().where(
(User.is_admin == True) &
(User.is_active == True))
# Find any users who are either administrators or super-users.
User.select().where(
(User.is_admin == True) |
(User.is_superuser == True))
# Find any Tweets by users who are not admins (NOT IN).
admins = User.select().where(User.is_admin == True)
non_admin_tweets = Tweet.select().where(Tweet.user.not_in(admins))
# Find any users who are not my friends (strangers).
friends = User.select().where(User.username.in_(['charlie', 'huey', 'mickey']))
strangers = User.select().where(User.id.not_in(friends))
WARNING:
Although you may be tempted to use python's in, and, or and not operators in your query expressions,
these will not work. The return value of an in expression is always coerced to a boolean value.
Similarly, and, or and not all treat their arguments as boolean values and cannot be overloaded.
So just remember:
• Use .in_() and .not_in() instead of in and not in
• Use & instead of and
• Use | instead of or
• Use ~ instead of not
• Use .is_null() instead of is None or == None.
• Don't forget to wrap your comparisons in parentheses when using logical operators.
For more examples, see the Expressions section.
NOTE:
LIKE and ILIKE with SQLite
Because SQLite's LIKE operation is case-insensitive by default, peewee will use the SQLite GLOB
operation for case-sensitive searches. The glob operation uses asterisks for wildcards as opposed to
the usual percent-sign. If you are using SQLite and want case-sensitive partial string matching,
remember to use asterisks for the wildcard.
Three valued logic
Because of the way SQL handles NULL, there are some special operations available for expressing:
• IS NULL
• IS NOT NULL
• IN
• NOT IN
While it would be possible to use the IS NULL and IN operators with the negation operator (~), sometimes
to get the correct semantics you will need to explicitly use IS NOT NULL and NOT IN.
The simplest way to use IS NULL and IN is to use the operator overloads:
# Get all User objects whose last login is NULL.
User.select().where(User.last_login >> None)
# Get users whose username is in the given list.
usernames = ['charlie', 'huey', 'mickey']
User.select().where(User.username << usernames)
If you don't like operator overloads, you can call the Field methods instead:
# Get all User objects whose last login is NULL.
User.select().where(User.last_login.is_null(True))
# Get users whose username is in the given list.
usernames = ['charlie', 'huey', 'mickey']
User.select().where(User.username.in_(usernames))
To negate the above queries, you can use unary negation, but for the correct semantics you may need to
use the special IS NOT and NOT IN operators:
# Get all User objects whose last login is *NOT* NULL.
User.select().where(User.last_login.is_null(False))
# Using unary negation instead.
User.select().where(~(User.last_login >> None))
# Get users whose username is *NOT* in the given list.
usernames = ['charlie', 'huey', 'mickey']
User.select().where(User.username.not_in(usernames))
# Using unary negation instead.
usernames = ['charlie', 'huey', 'mickey']
User.select().where(~(User.username << usernames))
Adding user-defined operators
Because I ran out of python operators to overload, there are some missing operators in peewee, for
instance modulo. If you find that you need to support an operator that is not in the table above, it is
very easy to add your own.
Here is how you might add support for modulo in SQLite:
from peewee import *
from peewee import Expression # the building block for expressions
def mod(lhs, rhs):
return Expression(lhs, '%', rhs)
Now you can use these custom operators to build richer queries:
# Users with even ids.
User.select().where(mod(User.id, 2) == 0)
For more examples check out the source to the playhouse.postgresql_ext module, as it contains numerous
operators specific to postgresql's hstore.
Expressions
Peewee is designed to provide a simple, expressive, and pythonic way of constructing SQL queries. This
section will provide a quick overview of some common types of expressions.
There are two primary types of objects that can be composed to create expressions:
• Field instances
• SQL aggregations and functions using fn
We will assume a simple "User" model with fields for username and other things. It looks like this:
class User(Model):
username = CharField()
is_admin = BooleanField()
is_active = BooleanField()
last_login = DateTimeField()
login_count = IntegerField()
failed_logins = IntegerField()
Comparisons use the Query operators:
# username is equal to 'charlie'
User.username == 'charlie'
# user has logged in less than 5 times
User.login_count < 5
Comparisons can be combined using bitwise and and or. Operator precedence is controlled by python and
comparisons can be nested to an arbitrary depth:
# User is both and admin and has logged in today
(User.is_admin == True) & (User.last_login >= today)
# User's username is either charlie or charles
(User.username == 'charlie') | (User.username == 'charles')
Comparisons can be used with functions as well:
# user's username starts with a 'g' or a 'G':
fn.Lower(fn.Substr(User.username, 1, 1)) == 'g'
We can do some fairly interesting things, as expressions can be compared against other expressions.
Expressions also support arithmetic operations:
# users who entered the incorrect more than half the time and have logged
# in at least 10 times
(User.failed_logins > (User.login_count * .5)) & (User.login_count > 10)
Expressions allow us to do atomic updates:
# when a user logs in we want to increment their login count:
User.update(login_count=User.login_count + 1).where(User.id == user_id)
Expressions can be used in all parts of a query, so experiment!
SQL Functions
SQL functions, like COUNT() or SUM(), can be expressed using the fn() helper:
# Get all users and the number of tweets they've authored. Sort the
# results from most tweets -> fewest tweets.
query = (User
.select(User, fn.COUNT(Tweet.id).alias('tweet_count'))
.join(Tweet, JOIN.LEFT_OUTER)
.group_by(User)
.order_by(fn.COUNT(Tweet.id).desc()))
for user in query:
print('%s -- %s tweets' % (user.username, user.tweet_count))
The fn helper exposes any SQL function as if it were a method. The parameters can be fields, values,
subqueries, or even nested functions.
Nesting function calls
Suppose you need to want to get a list of all users whose username begins with a. There are a couple ways
to do this, but one method might be to use some SQL functions like LOWER and SUBSTR. To use arbitrary SQL
functions, use the special fn() object to construct queries:
# Select the user's id, username and the first letter of their username, lower-cased
first_letter = fn.LOWER(fn.SUBSTR(User.username, 1, 1))
query = User.select(User, first_letter.alias('first_letter'))
# Alternatively we could select only users whose username begins with 'a'
a_users = User.select().where(first_letter == 'a')
>>> for user in a_users:
... print(user.username)
SQL Helper
There are times when you may want to simply pass in some arbitrary sql. You can do this using the special
SQL class. One use-case is when referencing an alias:
# We'll query the user table and annotate it with a count of tweets for
# the given user
query = (User
.select(User, fn.Count(Tweet.id).alias('ct'))
.join(Tweet)
.group_by(User))
# Now we will order by the count, which was aliased to "ct"
query = query.order_by(SQL('ct'))
# You could, of course, also write this as:
query = query.order_by(fn.COUNT(Tweet.id))
There are two ways to execute hand-crafted SQL statements with peewee:
1. Database.execute_sql() for executing any type of query
2. RawQuery for executing SELECT queries and returning model instances.
Security and SQL Injection
By default peewee will parameterize queries, so any parameters passed in by the user will be escaped. The
only exception to this rule is if you are writing a raw SQL query or are passing in a SQL object which
may contain untrusted data. To mitigate this, ensure that any user-defined data is passed in as a query
parameter and not part of the actual SQL query:
# Bad! DO NOT DO THIS!
query = MyModel.raw('SELECT * FROM my_table WHERE data = %s' % (user_data,))
# Good. `user_data` will be treated as a parameter to the query.
query = MyModel.raw('SELECT * FROM my_table WHERE data = %s', user_data)
# Bad! DO NOT DO THIS!
query = MyModel.select().where(SQL('Some SQL expression %s' % user_data))
# Good. `user_data` will be treated as a parameter.
query = MyModel.select().where(SQL('Some SQL expression %s', user_data))
NOTE:
MySQL and Postgresql use '%s' to denote parameters. SQLite, on the other hand, uses '?'. Be sure to
use the character appropriate to your database. You can also find this parameter by checking
Database.param.
Relationships and Joins
In this document we'll cover how Peewee handles relationships between models.
Model definitions
We'll use the following model definitions for our examples:
import datetime
from peewee import *
db = SqliteDatabase(':memory:')
class BaseModel(Model):
class Meta:
database = db
class User(BaseModel):
username = TextField()
class Tweet(BaseModel):
content = TextField()
timestamp = DateTimeField(default=datetime.datetime.now)
user = ForeignKeyField(User, backref='tweets')
class Favorite(BaseModel):
user = ForeignKeyField(User, backref='favorites')
tweet = ForeignKeyField(Tweet, backref='favorites')
Peewee uses ForeignKeyField to define foreign-key relationships between models. Every foreign-key field
has an implied back-reference, which is exposed as a pre-filtered Select query using the provided backref
attribute.
Creating test data
To follow along with the examples, let's populate this database with some test data:
def populate_test_data():
db.create_tables([User, Tweet, Favorite])
data = (
('huey', ('meow', 'hiss', 'purr')),
('mickey', ('woof', 'whine')),
('zaizee', ()))
for username, tweets in data:
user = User.create(username=username)
for tweet in tweets:
Tweet.create(user=user, content=tweet)
# Populate a few favorites for our users, such that:
favorite_data = (
('huey', ['whine']),
('mickey', ['purr']),
('zaizee', ['meow', 'purr']))
for username, favorites in favorite_data:
user = User.get(User.username == username)
for content in favorites:
tweet = Tweet.get(Tweet.content == content)
Favorite.create(user=user, tweet=tweet)
This gives us the following:
┌───────┬───────┬────────────────┐
│User │ Tweet │ Favorited by │
├───────┼───────┼────────────────┤
│huey │ meow │ zaizee │
└───────┴───────┴────────────────┘
│huey │ hiss │ │
├───────┼───────┼────────────────┤
│huey │ purr │ mickey, zaizee │
├───────┼───────┼────────────────┤
│mickey │ woof │ │
├───────┼───────┼────────────────┤
│mickey │ whine │ huey │
└───────┴───────┴────────────────┘
ATTENTION:
In the following examples we will be executing a number of queries. If you are unsure how many queries
are being executed, you can add the following code, which will log all queries to the console:
import logging
logger = logging.getLogger('peewee')
logger.addHandler(logging.StreamHandler())
logger.setLevel(logging.DEBUG)
NOTE:
In SQLite, foreign keys are not enabled by default. Most things, including the Peewee foreign-key API,
will work fine, but ON DELETE behaviour will be ignored, even if you explicitly specify on_delete in
your ForeignKeyField. In conjunction with the default AutoField behaviour (where deleted record IDs
can be reused), this can lead to subtle bugs. To avoid problems, I recommend that you enable
foreign-key constraints when using SQLite, by setting pragmas={'foreign_keys': 1} when you instantiate
SqliteDatabase.
# Ensure foreign-key constraints are enforced.
db = SqliteDatabase('my_app.db', pragmas={'foreign_keys': 1})
Performing simple joins
As an exercise in learning how to perform joins with Peewee, let's write a query to print out all the
tweets by "huey". To do this we'll select from the Tweet model and join on the User model, so we can then
filter on the User.username field:
>>> query = Tweet.select().join(User).where(User.username == 'huey')
>>> for tweet in query:
... print(tweet.content)
...
meow
hiss
purr
NOTE:
We did not have to explicitly specify the join predicate (the "ON" clause), because Peewee inferred
from the models that when we joined from Tweet to User, we were joining on the Tweet.user foreign-key.
The following code is equivalent, but more explicit:
query = (Tweet
.select()
.join(User, on=(Tweet.user == User.id))
.where(User.username == 'huey'))
If we already had a reference to the User object for "huey", we could use the User.tweets back-reference
to list all of huey's tweets:
>>> huey = User.get(User.username == 'huey')
>>> for tweet in huey.tweets:
... print(tweet.content)
...
meow
hiss
purr
Taking a closer look at huey.tweets, we can see that it is just a simple pre-filtered SELECT query:
>>> huey.tweets
<peewee.ModelSelect at 0x7f0483931fd0>
>>> huey.tweets.sql()
('SELECT "t1"."id", "t1"."content", "t1"."timestamp", "t1"."user_id"
FROM "tweet" AS "t1" WHERE ("t1"."user_id" = ?)', [1])
Joining multiple tables
Let's take another look at joins by querying the list of users and getting the count of how many tweet's
they've authored that were favorited. This will require us to join twice: from user to tweet, and from
tweet to favorite. We'll add the additional requirement that users should be included who have not
created any tweets, as well as users whose tweets have not been favorited. The query, expressed in SQL,
would be:
SELECT user.username, COUNT(favorite.id)
FROM user
LEFT OUTER JOIN tweet ON tweet.user_id = user.id
LEFT OUTER JOIN favorite ON favorite.tweet_id = tweet.id
GROUP BY user.username
NOTE:
In the above query both joins are LEFT OUTER, since a user may not have any tweets or, if they have
tweets, none of them may have been favorited.
Peewee has a concept of a join context, meaning that whenever we call the join() method, we are
implicitly joining on the previously-joined model (or if this is the first call, the model we are
selecting from). Since we are joining straight through, from user to tweet, then from tweet to favorite,
we can simply write:
query = (User
.select(User.username, fn.COUNT(Favorite.id).alias('count'))
.join(Tweet, JOIN.LEFT_OUTER) # Joins user -> tweet.
.join(Favorite, JOIN.LEFT_OUTER) # Joins tweet -> favorite.
.group_by(User.username))
Iterating over the results:
>>> for user in query:
... print(user.username, user.count)
...
huey 3
mickey 1
zaizee 0
For a more complicated example involving multiple joins and switching join contexts, let's find all the
tweets by Huey and the number of times they've been favorited. To do this we'll need to perform two joins
and we'll also use an aggregate function to calculate the favorite count.
Here is how we would write this query in SQL:
SELECT tweet.content, COUNT(favorite.id)
FROM tweet
INNER JOIN user ON tweet.user_id = user.id
LEFT OUTER JOIN favorite ON favorite.tweet_id = tweet.id
WHERE user.username = 'huey'
GROUP BY tweet.content;
NOTE:
We use a LEFT OUTER join from tweet to favorite since a tweet may not have any favorites, yet we still
wish to display it's content (along with a count of zero) in the result set.
With Peewee, the resulting Python code looks very similar to what we would write in SQL:
query = (Tweet
.select(Tweet.content, fn.COUNT(Favorite.id).alias('count'))
.join(User) # Join from tweet -> user.
.switch(Tweet) # Move "join context" back to tweet.
.join(Favorite, JOIN.LEFT_OUTER) # Join from tweet -> favorite.
.where(User.username == 'huey')
.group_by(Tweet.content))
Note the call to switch() - that instructs Peewee to set the join context back to Tweet. If we had
omitted the explicit call to switch, Peewee would have used User (the last model we joined) as the join
context and constructed the join from User to Favorite using the Favorite.user foreign-key, which would
have given us incorrect results.
If we wanted to omit the join-context switching we could instead use the join_from() method. The
following query is equivalent to the previous one:
query = (Tweet
.select(Tweet.content, fn.COUNT(Favorite.id).alias('count'))
.join_from(Tweet, User) # Join tweet -> user.
.join_from(Tweet, Favorite, JOIN.LEFT_OUTER) # Join tweet -> favorite.
.where(User.username == 'huey')
.group_by(Tweet.content))
We can iterate over the results of the above query to print the tweet's content and the favorite count:
>>> for tweet in query:
... print('%s favorited %d times' % (tweet.content, tweet.count))
...
meow favorited 1 times
hiss favorited 0 times
purr favorited 2 times
Selecting from multiple sources
If we wished to list all the tweets in the database, along with the username of their author, you might
try writing this:
>>> for tweet in Tweet.select():
... print(tweet.user.username, '->', tweet.content)
...
huey -> meow
huey -> hiss
huey -> purr
mickey -> woof
mickey -> whine
There is a big problem with the above loop: it executes an additional query for every tweet to look up
the tweet.user foreign-key. For our small table the performance penalty isn't obvious, but we would find
the delays grew as the number of rows increased.
If you're familiar with SQL, you might remember that it's possible to SELECT from multiple tables,
allowing us to get the tweet content and the username in a single query:
SELECT tweet.content, user.username
FROM tweet
INNER JOIN user ON tweet.user_id = user.id;
Peewee makes this quite easy. In fact, we only need to modify our query a little bit. We tell Peewee we
wish to select Tweet.content as well as the User.username field, then we include a join from tweet to
user. To make it a bit more obvious that it's doing the correct thing, we can ask Peewee to return the
rows as dictionaries.
>>> for row in Tweet.select(Tweet.content, User.username).join(User).dicts():
... print(row)
...
{'content': 'meow', 'username': 'huey'}
{'content': 'hiss', 'username': 'huey'}
{'content': 'purr', 'username': 'huey'}
{'content': 'woof', 'username': 'mickey'}
{'content': 'whine', 'username': 'mickey'}
Now we'll leave off the call to ".dicts()" and return the rows as Tweet objects. Notice that Peewee
assigns the username value to tweet.user.username -- NOT tweet.username! Because there is a foreign-key
from tweet to user, and we have selected fields from both models, Peewee will reconstruct the model-graph
for us:
>>> for tweet in Tweet.select(Tweet.content, User.username).join(User):
... print(tweet.user.username, '->', tweet.content)
...
huey -> meow
huey -> hiss
huey -> purr
mickey -> woof
mickey -> whine
If we wish to, we can control where Peewee puts the joined User instance in the above query, by
specifying an attr in the join() method:
>>> query = Tweet.select(Tweet.content, User.username).join(User, attr='author')
>>> for tweet in query:
... print(tweet.author.username, '->', tweet.content)
...
huey -> meow
huey -> hiss
huey -> purr
mickey -> woof
mickey -> whine
Conversely, if we simply wish all attributes we select to be attributes of the Tweet instance, we can add
a call to objects() at the end of our query (similar to how we called dicts()):
>>> for tweet in query.objects():
... print(tweet.username, '->', tweet.content)
...
huey -> meow
(etc)
More complex example
As a more complex example, in this query, we will write a single query that selects all the favorites,
along with the user who created the favorite, the tweet that was favorited, and that tweet's author.
In SQL we would write:
SELECT owner.username, tweet.content, author.username AS author
FROM favorite
INNER JOIN user AS owner ON (favorite.user_id = owner.id)
INNER JOIN tweet ON (favorite.tweet_id = tweet.id)
INNER JOIN user AS author ON (tweet.user_id = author.id);
Note that we are selecting from the user table twice - once in the context of the user who created the
favorite, and again as the author of the tweet.
With Peewee, we use Model.alias() to alias a model class so it can be referenced twice in a single query:
Owner = User.alias()
query = (Favorite
.select(Favorite, Tweet.content, User.username, Owner.username)
.join(Owner) # Join favorite -> user (owner of favorite).
.switch(Favorite)
.join(Tweet) # Join favorite -> tweet
.join(User)) # Join tweet -> user
We can iterate over the results and access the joined values in the following way. Note how Peewee has
resolved the fields from the various models we selected and reconstructed the model graph:
>>> for fav in query:
... print(fav.user.username, 'liked', fav.tweet.content, 'by', fav.tweet.user.username)
...
huey liked whine by mickey
mickey liked purr by huey
zaizee liked meow by huey
zaizee liked purr by huey
Subqueries
Peewee allows you to join on any table-like object, including subqueries or common table expressions
(CTEs). To demonstrate joining on a subquery, let's query for all users and their latest tweet.
Here is the SQL:
SELECT tweet.*, user.*
FROM tweet
INNER JOIN (
SELECT latest.user_id, MAX(latest.timestamp) AS max_ts
FROM tweet AS latest
GROUP BY latest.user_id) AS latest_query
ON ((tweet.user_id = latest_query.user_id) AND (tweet.timestamp = latest_query.max_ts))
INNER JOIN user ON (tweet.user_id = user.id)
We'll do this by creating a subquery which selects each user and the timestamp of their latest tweet.
Then we can query the tweets table in the outer query and join on the user and timestamp combination from
the subquery.
# Define our subquery first. We'll use an alias of the Tweet model, since
# we will be querying from the Tweet model directly in the outer query.
Latest = Tweet.alias()
latest_query = (Latest
.select(Latest.user, fn.MAX(Latest.timestamp).alias('max_ts'))
.group_by(Latest.user)
.alias('latest_query'))
# Our join predicate will ensure that we match tweets based on their
# timestamp *and* user_id.
predicate = ((Tweet.user == latest_query.c.user_id) &
(Tweet.timestamp == latest_query.c.max_ts))
# We put it all together, querying from tweet and joining on the subquery
# using the above predicate.
query = (Tweet
.select(Tweet, User) # Select all columns from tweet and user.
.join(latest_query, on=predicate) # Join tweet -> subquery.
.join_from(Tweet, User)) # Join from tweet -> user.
Iterating over the query, we can see each user and their latest tweet.
>>> for tweet in query:
... print(tweet.user.username, '->', tweet.content)
...
huey -> purr
mickey -> whine
There are a couple things you may not have seen before in the code we used to create the query in this
section:
• We used join_from() to explicitly specify the join context. We wrote .join_from(Tweet, User), which is
equivalent to .switch(Tweet).join(User).
• We referenced columns in the subquery using the magic .c attribute, for example latest_query.c.max_ts.
The .c attribute is used to dynamically create column references.
• Instead of passing individual fields to Tweet.select(), we passed the Tweet and User models. This is
shorthand for selecting all fields on the given model.
Common-table Expressions
In the previous section we joined on a subquery, but we could just as easily have used a common-table
expression (CTE). We will repeat the same query as before, listing users and their latest tweets, but
this time we will do it using a CTE.
Here is the SQL:
WITH latest AS (
SELECT user_id, MAX(timestamp) AS max_ts
FROM tweet
GROUP BY user_id)
SELECT tweet.*, user.*
FROM tweet
INNER JOIN latest
ON ((latest.user_id = tweet.user_id) AND (latest.max_ts = tweet.timestamp))
INNER JOIN user
ON (tweet.user_id = user.id)
This example looks very similar to the previous example with the subquery:
# Define our CTE first. We'll use an alias of the Tweet model, since
# we will be querying from the Tweet model directly in the main query.
Latest = Tweet.alias()
cte = (Latest
.select(Latest.user, fn.MAX(Latest.timestamp).alias('max_ts'))
.group_by(Latest.user)
.cte('latest'))
# Our join predicate will ensure that we match tweets based on their
# timestamp *and* user_id.
predicate = ((Tweet.user == cte.c.user_id) &
(Tweet.timestamp == cte.c.max_ts))
# We put it all together, querying from tweet and joining on the CTE
# using the above predicate.
query = (Tweet
.select(Tweet, User) # Select all columns from tweet and user.
.join(cte, on=predicate) # Join tweet -> CTE.
.join_from(Tweet, User) # Join from tweet -> user.
.with_cte(cte))
We can iterate over the result-set, which consists of the latest tweets for each user:
>>> for tweet in query:
... print(tweet.user.username, '->', tweet.content)
...
huey -> purr
mickey -> whine
NOTE:
For more information about using CTEs, including information on writing recursive CTEs, see the cte
section of the "Querying" document.
Multiple foreign-keys to the same Model
When there are multiple foreign keys to the same model, it is good practice to explicitly specify which
field you are joining on.
Referring back to the example app's models, consider the Relationship model, which is used to denote when
one user follows another. Here is the model definition:
class Relationship(BaseModel):
from_user = ForeignKeyField(User, backref='relationships')
to_user = ForeignKeyField(User, backref='related_to')
class Meta:
indexes = (
# Specify a unique multi-column index on from/to-user.
(('from_user', 'to_user'), True),
)
Since there are two foreign keys to User, we should always specify which field we are using in a join.
For example, to determine which users I am following, I would write:
(User
.select()
.join(Relationship, on=Relationship.to_user)
.where(Relationship.from_user == charlie))
On the other hand, if I wanted to determine which users are following me, I would instead join on the
from_user column and filter on the relationship's to_user:
(User
.select()
.join(Relationship, on=Relationship.from_user)
.where(Relationship.to_user == charlie))
Joining on arbitrary fields
If a foreign key does not exist between two tables you can still perform a join, but you must manually
specify the join predicate.
In the following example, there is no explicit foreign-key between User and ActivityLog, but there is an
implied relationship between the ActivityLog.object_id field and User.id. Rather than joining on a
specific Field, we will join using an Expression.
user_log = (User
.select(User, ActivityLog)
.join(ActivityLog, on=(User.id == ActivityLog.object_id), attr='log')
.where(
(ActivityLog.activity_type == 'user_activity') &
(User.username == 'charlie')))
for user in user_log:
print(user.username, user.log.description)
#### Print something like ####
charlie logged in
charlie posted a tweet
charlie retweeted
charlie posted a tweet
charlie logged out
NOTE:
Recall that we can control the attribute Peewee will assign the joined instance to by specifying the
attr parameter in the join() method. In the previous example, we used the following join:
join(ActivityLog, on=(User.id == ActivityLog.object_id), attr='log')
Then when iterating over the query, we were able to directly access the joined ActivityLog without
incurring an additional query:
for user in user_log:
print(user.username, user.log.description)
Self-joins
Peewee supports constructing queries containing a self-join.
Using model aliases
To join on the same model (table) twice, it is necessary to create a model alias to represent the second
instance of the table in a query. Consider the following model:
class Category(Model):
name = CharField()
parent = ForeignKeyField('self', backref='children')
What if we wanted to query all categories whose parent category is Electronics. One way would be to
perform a self-join:
Parent = Category.alias()
query = (Category
.select()
.join(Parent, on=(Category.parent == Parent.id))
.where(Parent.name == 'Electronics'))
When performing a join that uses a ModelAlias, it is necessary to specify the join condition using the on
keyword argument. In this case we are joining the category with its parent category.
Using subqueries
Another less common approach involves the use of subqueries. Here is another way we might construct a
query to get all the categories whose parent category is Electronics using a subquery:
Parent = Category.alias()
join_query = Parent.select().where(Parent.name == 'Electronics')
# Subqueries used as JOINs need to have an alias.
join_query = join_query.alias('jq')
query = (Category
.select()
.join(join_query, on=(Category.parent == join_query.c.id)))
This will generate the following SQL query:
SELECT t1."id", t1."name", t1."parent_id"
FROM "category" AS t1
INNER JOIN (
SELECT t2."id"
FROM "category" AS t2
WHERE (t2."name" = ?)) AS jq ON (t1."parent_id" = "jq"."id")
To access the id value from the subquery, we use the .c magic lookup which will generate the appropriate
SQL expression:
Category.parent == join_query.c.id
# Becomes: (t1."parent_id" = "jq"."id")
Implementing Many to Many
Peewee provides a field for representing many-to-many relationships, much like Django does. This feature
was added due to many requests from users, but I strongly advocate against using it, since it conflates
the idea of a field with a junction table and hidden joins. It's just a nasty hack to provide convenient
accessors.
To implement many-to-many correctly with peewee, you will therefore create the intermediary table
yourself and query through it:
class Student(Model):
name = CharField()
class Course(Model):
name = CharField()
class StudentCourse(Model):
student = ForeignKeyField(Student)
course = ForeignKeyField(Course)
To query, let's say we want to find students who are enrolled in math class:
query = (Student
.select()
.join(StudentCourse)
.join(Course)
.where(Course.name == 'math'))
for student in query:
print(student.name)
To query what classes a given student is enrolled in:
courses = (Course
.select()
.join(StudentCourse)
.join(Student)
.where(Student.name == 'da vinci'))
for course in courses:
print(course.name)
To efficiently iterate over a many-to-many relation, i.e., list all students and their respective
courses, we will query the through model StudentCourse and precompute the Student and Course:
query = (StudentCourse
.select(StudentCourse, Student, Course)
.join(Course)
.switch(StudentCourse)
.join(Student)
.order_by(Student.name))
To print a list of students and their courses you might do the following:
for student_course in query:
print(student_course.student.name, '->', student_course.course.name)
Since we selected all fields from Student and Course in the select clause of the query, these foreign key
traversals are "free" and we've done the whole iteration with just 1 query.
ManyToManyField
The ManyToManyField provides a field-like API over many-to-many fields. For all but the simplest
many-to-many situations, you're better off using the standard peewee APIs. But, if your models are very
simple and your querying needs are not very complex, ManyToManyField may work.
Modeling students and courses using ManyToManyField:
from peewee import *
from playhouse.fields import ManyToManyField
db = SqliteDatabase('school.db')
class BaseModel(Model):
class Meta:
database = db
class Student(BaseModel):
name = CharField()
class Course(BaseModel):
name = CharField()
students = ManyToManyField(Student, backref='courses')
StudentCourse = Course.students.get_through_model()
db.create_tables([
Student,
Course,
StudentCourse])
# Get all classes that "huey" is enrolled in:
huey = Student.get(Student.name == 'Huey')
for course in huey.courses.order_by(Course.name):
print(course.name)
# Get all students in "English 101":
engl_101 = Course.get(Course.name == 'English 101')
for student in engl_101.students:
print(student.name)
# When adding objects to a many-to-many relationship, we can pass
# in either a single model instance, a list of models, or even a
# query of models:
huey.courses.add(Course.select().where(Course.name.contains('English')))
engl_101.students.add(Student.get(Student.name == 'Mickey'))
engl_101.students.add([
Student.get(Student.name == 'Charlie'),
Student.get(Student.name == 'Zaizee')])
# The same rules apply for removing items from a many-to-many:
huey.courses.remove(Course.select().where(Course.name.startswith('CS')))
engl_101.students.remove(huey)
# Calling .clear() will remove all associated objects:
cs_150.students.clear()
ATTENTION:
Before many-to-many relationships can be added, the objects being referenced will need to be saved
first. In order to create relationships in the many-to-many through table, Peewee needs to know the
primary keys of the models being referenced.
For more examples, see:
• ManyToManyField.add()
• ManyToManyField.remove()
• ManyToManyField.clear()
• ManyToManyField.get_through_model()
Avoiding the N+1 problem
The N+1 problem refers to a situation where an application performs a query, then for each row of the
result set, the application performs at least one other query (another way to conceptualize this is as a
nested loop). In many cases, these n queries can be avoided through the use of a SQL join or subquery.
The database itself may do a nested loop, but it will usually be more performant than doing n queries in
your application code, which involves latency communicating with the database and may not take advantage
of indices or other optimizations employed by the database when joining or executing a subquery.
Peewee provides several APIs for mitigating N+1 query behavior. Recollecting the models used throughout
this document, User and Tweet, this section will try to outline some common N+1 scenarios, and how peewee
can help you avoid them.
ATTENTION:
In some cases, N+1 queries will not result in a significant or measurable performance hit. It all
depends on the data you are querying, the database you are using, and the latency involved in
executing queries and retrieving results. As always when making optimizations, profile before and
after to ensure the changes do what you expect them to.
List recent tweets
The twitter timeline displays a list of tweets from multiple users. In addition to the tweet's content,
the username of the tweet's author is also displayed. The N+1 scenario here would be:
1. Fetch the 10 most recent tweets.
2. For each tweet, select the author (10 queries).
By selecting both tables and using a join, peewee makes it possible to accomplish this in a single query:
query = (Tweet
.select(Tweet, User) # Note that we are selecting both models.
.join(User) # Use an INNER join because every tweet has an author.
.order_by(Tweet.id.desc()) # Get the most recent tweets.
.limit(10))
for tweet in query:
print(tweet.user.username, '-', tweet.message)
Without the join, accessing tweet.user.username would trigger a query to resolve the foreign key
tweet.user and retrieve the associated user. But since we have selected and joined on User, peewee will
automatically resolve the foreign-key for us.
NOTE:
This technique is discussed in more detail in Selecting from multiple sources.
List users and all their tweets
Let's say you want to build a page that shows several users and all of their tweets. The N+1 scenario
would be:
1. Fetch some users.
2. For each user, fetch their tweets.
This situation is similar to the previous example, but there is one important difference: when we
selected tweets, they only have a single associated user, so we could directly assign the foreign key.
The reverse is not true, however, as one user may have any number of tweets (or none at all).
Peewee provides an approach to avoiding O(n) queries in this situation. Fetch users first, then fetch all
the tweets associated with those users. Once peewee has the big list of tweets, it will assign them out,
matching them with the appropriate user. This method is usually faster but will involve a query for each
table being selected.
Using prefetch
peewee supports pre-fetching related data using sub-queries. This method requires the use of a special
API, prefetch(). Prefetch, as its name implies, will eagerly load the appropriate tweets for the given
users using subqueries. This means instead of O(n) queries for n rows, we will do O(k) queries for k
tables.
Here is an example of how we might fetch several users and any tweets they created within the past week.
week_ago = datetime.date.today() - datetime.timedelta(days=7)
users = User.select()
tweets = (Tweet
.select()
.where(Tweet.timestamp >= week_ago))
# This will perform two queries.
users_with_tweets = prefetch(users, tweets)
for user in users_with_tweets:
print(user.username)
for tweet in user.tweets:
print(' ', tweet.message)
NOTE:
Note that neither the User query, nor the Tweet query contained a JOIN clause. When using prefetch()
you do not need to specify the join.
prefetch() can be used to query an arbitrary number of tables. Check the API documentation for more
examples.
Some things to consider when using prefetch():
• Foreign keys must exist between the models being prefetched.
• LIMIT works as you'd expect on the outer-most query, but may be difficult to implement correctly if
trying to limit the size of the sub-selects.
API Documentation
This document specifies Peewee's APIs.
Database
class Database(database[, thread_safe=True[, autorollback=False[, field_types=None[, operations=None[,
**kwargs]]]]])
Parameters
• database (str) -- Database name or filename for SQLite (or None to defer initialization,
in which case you must call Database.init(), specifying the database name).
• thread_safe (bool) -- Whether to store connection state in a thread-local.
• autorollback (bool) -- Automatically rollback queries that fail when not in an explicit
transaction.
• field_types (dict) -- A mapping of additional field types to support.
• operations (dict) -- A mapping of additional operations to support.
• kwargs -- Arbitrary keyword arguments that will be passed to the database driver when a
connection is created, for example password, host, etc.
The Database is responsible for:
• Executing queries
• Managing connections
• Transactions
• Introspection
NOTE:
The database can be instantiated with None as the database name if the database is not known
until run-time. In this way you can create a database instance and then configure it elsewhere
when the settings are known. This is called deferred* initialization.
Examples:
# Sqlite database using WAL-mode and 32MB page-cache.
db = SqliteDatabase('app.db', pragmas={
'journal_mode': 'wal',
'cache_size': -32 * 1000})
# Postgresql database on remote host.
db = PostgresqlDatabase('my_app', user='postgres', host='10.1.0.3',
password='secret')
Deferred initialization example:
db = PostgresqlDatabase(None)
class BaseModel(Model):
class Meta:
database = db
# Read database connection info from env, for example:
db_name = os.environ['DATABASE']
db_host = os.environ['PGHOST']
# Initialize database.
db.init(db_name, host=db_host, user='postgres')
param = '?'
String used as parameter placeholder in SQL queries.
quote = '"'
Type of quotation-mark to use to denote entities such as tables or columns.
init(database[, **kwargs])
Parameters
• database (str) -- Database name or filename for SQLite.
• kwargs -- Arbitrary keyword arguments that will be passed to the database driver
when a connection is created, for example password, host, etc.
Initialize a deferred database. See deferring_initialization for more info.
__enter__()
The Database instance can be used as a context-manager, in which case a connection will be
held open for the duration of the wrapped block.
Additionally, any SQL executed within the wrapped block will be executed in a transaction.
connection_context()
Create a context-manager that will hold open a connection for the duration of the wrapped
block.
Example:
def on_app_startup():
# When app starts up, create the database tables, being sure
# the connection is closed upon completion.
with database.connection_context():
database.create_tables(APP_MODELS)
connect([reuse_if_open=False])
Parameters
reuse_if_open (bool) -- Do not raise an exception if a connection is already opened.
Returns
whether a new connection was opened.
Return type
bool
Raises OperationalError if connection already open and reuse_if_open is not set to True.
Open a connection to the database.
close()
Returns
Whether a connection was closed. If the database was already closed, this returns
False.
Return type
bool
Close the connection to the database.
is_closed()
Returns
return True if database is closed, False if open.
Return type
bool
connection()
Return the open connection. If a connection is not open, one will be opened. The connection
will be whatever the underlying database-driver uses to encapsulate a database connection.
cursor([commit=None])
Parameters
commit -- For internal use.
Return a cursor object on the current connection. If a connection is not open, one will be
opened. The cursor will be whatever the underlying database-driver uses to encapsulate a
database cursor.
execute_sql(sql[, params=None[, commit=SENTINEL]])
Parameters
• sql (str) -- SQL string to execute.
• params (tuple) -- Parameters for query.
• commit -- Boolean flag to override the default commit logic.
Returns
cursor object.
Execute a SQL query and return a cursor over the results.
execute(query[, commit=SENTINEL[, **context_options]])
Parameters
• query -- A Query instance.
• commit -- Boolean flag to override the default commit logic.
• context_options -- Arbitrary options to pass to the SQL generator.
Returns
cursor object.
Execute a SQL query by compiling a Query instance and executing the resulting SQL.
last_insert_id(cursor[, query_type=None])
Parameters
cursor -- cursor object.
Returns
primary key of last-inserted row.
rows_affected(cursor)
Parameters
cursor -- cursor object.
Returns
number of rows modified by query.
in_transaction()
Returns
whether or not a transaction is currently open.
Return type
bool
atomic()
Create a context-manager which runs any queries in the wrapped block in a transaction (or
save-point if blocks are nested).
Calls to atomic() can be nested.
atomic() can also be used as a decorator.
Example code:
with db.atomic() as txn:
perform_operation()
with db.atomic() as nested_txn:
perform_another_operation()
Transactions and save-points can be explicitly committed or rolled-back within the wrapped
block. If this occurs, a new transaction or savepoint is begun after the commit/rollback.
Example:
with db.atomic() as txn:
User.create(username='mickey')
txn.commit() # Changes are saved and a new transaction begins.
User.create(username='huey')
txn.rollback() # "huey" will not be saved.
User.create(username='zaizee')
# Print the usernames of all users.
print [u.username for u in User.select()]
# Prints ["mickey", "zaizee"]
manual_commit()
Create a context-manager which disables all transaction management for the duration of the
wrapped block.
Example:
with db.manual_commit():
db.begin() # Begin transaction explicitly.
try:
user.delete_instance(recursive=True)
except:
db.rollback() # Rollback -- an error occurred.
raise
else:
try:
db.commit() # Attempt to commit changes.
except:
db.rollback() # Error committing, rollback.
raise
The above code is equivalent to the following:
with db.atomic():
user.delete_instance(recursive=True)
transaction()
Create a context-manager that runs all queries in the wrapped block in a transaction.
WARNING:
Calls to transaction cannot be nested. Only the top-most call will take effect.
Rolling-back or committing a nested transaction context-manager has undefined behavior.
savepoint()
Create a context-manager that runs all queries in the wrapped block in a savepoint.
Savepoints can be nested arbitrarily.
WARNING:
Calls to savepoint must occur inside of a transaction.
begin()
Begin a transaction when using manual-commit mode.
NOTE:
This method should only be used in conjunction with the manual_commit() context manager.
commit()
Manually commit the currently-active transaction.
NOTE:
This method should only be used in conjunction with the manual_commit() context manager.
rollback()
Manually roll-back the currently-active transaction.
NOTE:
This method should only be used in conjunction with the manual_commit() context manager.
batch_commit(it, n)
Parameters
• it (iterable) -- an iterable whose items will be yielded.
• n (int) -- commit every n items.
Returns
an equivalent iterable to the one provided, with the addition that groups of n items
will be yielded in a transaction.
The purpose of this method is to simplify batching large operations, such as inserts,
updates, etc. You pass in an iterable and the number of items-per-batch, and the items will
be returned by an equivalent iterator that wraps each batch in a transaction.
Example:
# Some list or iterable containing data to insert.
row_data = [{'username': 'u1'}, {'username': 'u2'}, ...]
# Insert all data, committing every 100 rows. If, for example,
# there are 789 items in the list, then there will be a total of
# 8 transactions (7x100 and 1x89).
for row in db.batch_commit(row_data, 100):
User.create(**row)
An alternative that may be more efficient is to batch the data into a multi-value INSERT
statement (for example, using Model.insert_many()):
with db.atomic():
for idx in range(0, len(row_data), 100):
# Insert 100 rows at a time.
rows = row_data[idx:idx + 100]
User.insert_many(rows).execute()
table_exists(table[, schema=None])
Parameters
• table (str) -- Table name.
• schema (str) -- Schema name (optional).
Returns
bool indicating whether table exists.
get_tables([schema=None])
Parameters
schema (str) -- Schema name (optional).
Returns
a list of table names in the database.
get_indexes(table[, schema=None])
Parameters
• table (str) -- Table name.
• schema (str) -- Schema name (optional).
Return a list of IndexMetadata tuples.
Example:
print(db.get_indexes('entry'))
[IndexMetadata(
name='entry_public_list',
sql='CREATE INDEX "entry_public_list" ...',
columns=['timestamp'],
unique=False,
table='entry'),
IndexMetadata(
name='entry_slug',
sql='CREATE UNIQUE INDEX "entry_slug" ON "entry" ("slug")',
columns=['slug'],
unique=True,
table='entry')]
get_columns(table[, schema=None])
Parameters
• table (str) -- Table name.
• schema (str) -- Schema name (optional).
Return a list of ColumnMetadata tuples.
Example:
print(db.get_columns('entry'))
[ColumnMetadata(
name='id',
data_type='INTEGER',
null=False,
primary_key=True,
table='entry'),
ColumnMetadata(
name='title',
data_type='TEXT',
null=False,
primary_key=False,
table='entry'),
...]
get_primary_keys(table[, schema=None])
Parameters
• table (str) -- Table name.
• schema (str) -- Schema name (optional).
Return a list of column names that comprise the primary key.
Example:
print(db.get_primary_keys('entry'))
['id']
get_foreign_keys(table[, schema=None])
Parameters
• table (str) -- Table name.
• schema (str) -- Schema name (optional).
Return a list of ForeignKeyMetadata tuples for keys present on the table.
Example:
print(db.get_foreign_keys('entrytag'))
[ForeignKeyMetadata(
column='entry_id',
dest_table='entry',
dest_column='id',
table='entrytag'),
...]
get_views([schema=None])
Parameters
schema (str) -- Schema name (optional).
Return a list of ViewMetadata tuples for VIEWs present in the database.
Example:
print(db.get_views())
[ViewMetadata(
name='entries_public',
sql='CREATE VIEW entries_public AS SELECT ... '),
...]
sequence_exists(seq)
Parameters
seq (str) -- Name of sequence.
Returns
Whether sequence exists.
Return type
bool
create_tables(models[, **options])
Parameters
• models (list) -- A list of Model classes.
• options -- Options to specify when calling Model.create_table().
Create tables, indexes and associated metadata for the given list of models.
Dependencies are resolved so that tables are created in the appropriate order.
drop_tables(models[, **options])
Parameters
• models (list) -- A list of Model classes.
• kwargs -- Options to specify when calling Model.drop_table().
Drop tables, indexes and associated metadata for the given list of models.
Dependencies are resolved so that tables are dropped in the appropriate order.
bind(models[, bind_refs=True[, bind_backrefs=True]])
Parameters
• models (list) -- One or more Model classes to bind.
• bind_refs (bool) -- Bind related models.
• bind_backrefs (bool) -- Bind back-reference related models.
Bind the given list of models, and specified relations, to the database.
bind_ctx(models[, bind_refs=True[, bind_backrefs=True]])
Parameters
• models (list) -- List of models to bind to the database.
• bind_refs (bool) -- Bind models that are referenced using foreign-keys.
• bind_backrefs (bool) -- Bind models that reference the given model with a
foreign-key.
Create a context-manager that binds (associates) the given models with the current database
for the duration of the wrapped block.
Example:
MODELS = (User, Account, Note)
# Bind the given models to the db for the duration of wrapped block.
def use_test_database(fn):
@wraps(fn)
def inner(self):
with test_db.bind_ctx(MODELS):
test_db.create_tables(MODELS)
try:
fn(self)
finally:
test_db.drop_tables(MODELS)
return inner
class TestSomething(TestCase):
@use_test_database
def test_something(self):
# ... models are bound to test database ...
pass
class SqliteDatabase(database[, pragmas=None[, timeout=5[, **kwargs]]])
Parameters
• pragmas -- Either a dictionary or a list of 2-tuples containing pragma key and value to
set every time a connection is opened.
• timeout -- Set the busy-timeout on the SQLite driver (in seconds).
Sqlite database implementation. SqliteDatabase that provides some advanced features only offered
by Sqlite.
• Register custom aggregates, collations and functions
• Load C extensions
• Advanced transactions (specify lock type)
• For even more features, see SqliteExtDatabase.
Example of initializing a database and configuring some PRAGMAs:
db = SqliteDatabase('my_app.db', pragmas=(
('cache_size', -16000), # 16MB
('journal_mode', 'wal'), # Use write-ahead-log journal mode.
))
# Alternatively, pragmas can be specified using a dictionary.
db = SqliteDatabase('my_app.db', pragmas={'journal_mode': 'wal'})
pragma(key[, value=SENTINEL[, permanent=False]])
Parameters
• key -- Setting name.
• value -- New value for the setting (optional).
• permanent -- Apply this pragma whenever a connection is opened.
Execute a PRAGMA query once on the active connection. If a value is not specified, then the
current value will be returned.
If permanent is specified, then the PRAGMA query will also be executed whenever a new
connection is opened, ensuring it is always in-effect.
NOTE:
By default this only affects the current connection. If the PRAGMA being executed is not
persistent, then you must specify permanent=True to ensure the pragma is set on
subsequent connections.
cache_size
Get or set the cache_size pragma for the current connection.
foreign_keys
Get or set the foreign_keys pragma for the current connection.
journal_mode
Get or set the journal_mode pragma.
journal_size_limit
Get or set the journal_size_limit pragma.
mmap_size
Get or set the mmap_size pragma for the current connection.
page_size
Get or set the page_size pragma.
read_uncommitted
Get or set the read_uncommitted pragma for the current connection.
synchronous
Get or set the synchronous pragma for the current connection.
wal_autocheckpoint
Get or set the wal_autocheckpoint pragma for the current connection.
timeout
Get or set the busy timeout (seconds).
register_aggregate(klass[, name=None[, num_params=-1]])
Parameters
• klass -- Class implementing aggregate API.
• name (str) -- Aggregate function name (defaults to name of class).
• num_params (int) -- Number of parameters the aggregate accepts, or -1 for any
number.
Register a user-defined aggregate function.
The function will be registered each time a new connection is opened. Additionally, if a
connection is already open, the aggregate will be registered with the open connection.
aggregate([name=None[, num_params=-1]])
Parameters
• name (str) -- Name of the aggregate (defaults to class name).
• num_params (int) -- Number of parameters the aggregate accepts, or -1 for any
number.
Class decorator to register a user-defined aggregate function.
Example:
@db.aggregate('md5')
class MD5(object):
def initialize(self):
self.md5 = hashlib.md5()
def step(self, value):
self.md5.update(value)
def finalize(self):
return self.md5.hexdigest()
@db.aggregate()
class Product(object):
'''Like SUM() except calculates cumulative product.'''
def __init__(self):
self.product = 1
def step(self, value):
self.product *= value
def finalize(self):
return self.product
register_collation(fn[, name=None])
Parameters
• fn -- The collation function.
• name (str) -- Name of collation (defaults to function name)
Register a user-defined collation. The collation will be registered each time a new
connection is opened. Additionally, if a connection is already open, the collation will be
registered with the open connection.
collation([name=None])
Parameters
name (str) -- Name of collation (defaults to function name)
Decorator to register a user-defined collation.
Example:
@db.collation('reverse')
def collate_reverse(s1, s2):
return -cmp(s1, s2)
# Usage:
Book.select().order_by(collate_reverse.collation(Book.title))
# Equivalent:
Book.select().order_by(Book.title.asc(collation='reverse'))
As you might have noticed, the original collate_reverse function has a special attribute
called collation attached to it. This extra attribute provides a shorthand way to generate
the SQL necessary to use our custom collation.
register_function(fn[, name=None[, num_params=-1]])
Parameters
• fn -- The user-defined scalar function.
• name (str) -- Name of function (defaults to function name)
• num_params (int) -- Number of arguments the function accepts, or -1 for any
number.
Register a user-defined scalar function. The function will be registered each time a new
connection is opened. Additionally, if a connection is already open, the function will be
registered with the open connection.
func([name=None[, num_params=-1]])
Parameters
• name (str) -- Name of the function (defaults to function name).
• num_params (int) -- Number of parameters the function accepts, or -1 for any
number.
Decorator to register a user-defined scalar function.
Example:
@db.func('title_case')
def title_case(s):
return s.title() if s else ''
# Usage:
title_case_books = Book.select(fn.title_case(Book.title))
register_window_function(klass[, name=None[, num_params=-1]])
Parameters
• klass -- Class implementing window function API.
• name (str) -- Window function name (defaults to name of class).
• num_params (int) -- Number of parameters the function accepts, or -1 for any
number.
Register a user-defined window function.
ATTENTION:
This feature requires SQLite >= 3.25.0 and pysqlite3 >= 0.2.0.
The window function will be registered each time a new connection is opened. Additionally,
if a connection is already open, the window function will be registered with the open
connection.
window_function([name=None[, num_params=-1]])
Parameters
• name (str) -- Name of the window function (defaults to class name).
• num_params (int) -- Number of parameters the function accepts, or -1 for any
number.
Class decorator to register a user-defined window function. Window functions must define
the following methods:
• step(<params>) - receive values from a row and update state.
• inverse(<params>) - inverse of step() for the given values.
• value() - return the current value of the window function.
• finalize() - return the final value of the window function.
Example:
@db.window_function('my_sum')
class MySum(object):
def __init__(self):
self._value = 0
def step(self, value):
self._value += value
def inverse(self, value):
self._value -= value
def value(self):
return self._value
def finalize(self):
return self._value
table_function([name=None])
Class-decorator for registering a TableFunction. Table functions are user-defined functions
that, rather than returning a single, scalar value, can return any number of rows of
tabular data.
Example:
from playhouse.sqlite_ext import TableFunction
@db.table_function('series')
class Series(TableFunction):
columns = ['value']
params = ['start', 'stop', 'step']
def initialize(self, start=0, stop=None, step=1):
"""
Table-functions declare an initialize() method, which is
called with whatever arguments the user has called the
function with.
"""
self.start = self.current = start
self.stop = stop or float('Inf')
self.step = step
def iterate(self, idx):
"""
Iterate is called repeatedly by the SQLite database engine
until the required number of rows has been read **or** the
function raises a `StopIteration` signalling no more rows
are available.
"""
if self.current > self.stop:
raise StopIteration
ret, self.current = self.current, self.current + self.step
return (ret,)
# Usage:
cursor = db.execute_sql('SELECT * FROM series(?, ?, ?)', (0, 5, 2))
for value, in cursor:
print(value)
# Prints:
# 0
# 2
# 4
unregister_aggregate(name)
Parameters
name -- Name of the user-defined aggregate function.
Unregister the user-defined aggregate function.
unregister_collation(name)
Parameters
name -- Name of the user-defined collation.
Unregister the user-defined collation.
unregister_function(name)
Parameters
name -- Name of the user-defined scalar function.
Unregister the user-defined scalar function.
unregister_table_function(name)
Parameters
name -- Name of the user-defined table function.
Returns
True or False, depending on whether the function was removed.
Unregister the user-defined scalar function.
load_extension(extension_module)
Load the given C extension. If a connection is currently open in the calling thread, then
the extension will be loaded for that connection as well as all subsequent connections.
For example, if you've compiled the closure table extension and wish to use it in your
application, you might write:
db = SqliteExtDatabase('my_app.db')
db.load_extension('closure')
attach(filename, name)
Parameters
• filename (str) -- Database to attach (or :memory: for in-memory)
• name (str) -- Schema name for attached database.
Returns
boolean indicating success
Register another database file that will be attached to every database connection. If the
main database is currently connected, the new database will be attached on the open
connection.
NOTE:
Databases that are attached using this method will be attached every time a database
connection is opened.
detach(name)
Parameters
name (str) -- Schema name for attached database.
Returns
boolean indicating success
Unregister another database file that was attached previously with a call to attach(). If
the main database is currently connected, the attached database will be detached from the
open connection.
transaction([lock_type=None])
Parameters
lock_type (str) -- Locking strategy: DEFERRED, IMMEDIATE, EXCLUSIVE.
Create a transaction context-manager using the specified locking strategy (defaults to
DEFERRED).
class PostgresqlDatabase(database[, register_unicode=True[, encoding=None]])
Postgresql database implementation.
Additional optional keyword-parameters:
Parameters
• register_unicode (bool) -- Register unicode types.
• encoding (str) -- Database encoding.
class MySQLDatabase(database[, **kwargs])
MySQL database implementation.
Query-builder
class Node
Base-class for all components which make up the AST for a SQL query.
static copy(method)
Decorator to use with Node methods that mutate the node's state. This allows
method-chaining, e.g.:
query = MyModel.select()
new_query = query.where(MyModel.field == 'value')
unwrap()
API for recursively unwrapping "wrapped" nodes. Base case is to return self.
is_alias()
API for determining if a node, at any point, has been explicitly aliased by the user.
class Source([alias=None])
A source of row tuples, for example a table, join, or select query. By default provides a "magic"
attribute named "c" that is a factory for column/attribute lookups, for example:
User = Table('users')
query = (User
.select(User.c.username)
.where(User.c.active == True)
.order_by(User.c.username))
alias(name)
Returns a copy of the object with the given alias applied.
select(*columns)
Parameters
columns -- Column instances, expressions, functions, sub-queries, or anything else
that you would like to select.
Create a Select query on the table. If the table explicitly declares columns and no columns
are provided, then by default all the table's defined columns will be selected.
join(dest[, join_type='INNER'[, on=None]])
Parameters
• dest (Source) -- Join the table with the given destination.
• join_type (str) -- Join type.
• on -- Expression to use as join predicate.
Returns
a Join instance.
Join type may be one of:
• JOIN.INNER
• JOIN.LEFT_OUTER
• JOIN.RIGHT_OUTER
• JOIN.FULL
• JOIN.FULL_OUTER
• JOIN.CROSS
left_outer_join(dest[, on=None])
Parameters
• dest (Source) -- Join the table with the given destination.
• on -- Expression to use as join predicate.
Returns
a Join instance.
Convenience method for calling join() using a LEFT OUTER join.
class BaseTable
Base class for table-like objects, which support JOINs via operator overloading.
__and__(dest)
Perform an INNER join on dest.
__add__(dest)
Perform a LEFT OUTER join on dest.
__sub__(dest)
Perform a RIGHT OUTER join on dest.
__or__(dest)
Perform a FULL OUTER join on dest.
__mul__(dest)
Perform a CROSS join on dest.
class Table(name[, columns=None[, primary_key=None[, schema=None[, alias=None]]]])
Represents a table in the database (or a table-like object such as a view).
Parameters
• name (str) -- Database table name
• columns (tuple) -- List of column names (optional).
• primary_key (str) -- Name of primary key column.
• schema (str) -- Schema name used to access table (if necessary).
• alias (str) -- Alias to use for table in SQL queries.
NOTE:
If columns are specified, the magic "c" attribute will be disabled.
When columns are not explicitly defined, tables have a special attribute "c" which is a factory
that provides access to table columns dynamically.
Example:
User = Table('users')
query = (User
.select(User.c.id, User.c.username)
.order_by(User.c.username))
Equivalent example when columns are specified:
User = Table('users', ('id', 'username'))
query = (User
.select(User.id, User.username)
.order_by(User.username))
bind([database=None])
Parameters
database -- Database object.
Bind this table to the given database (or unbind by leaving empty).
When a table is bound to a database, queries may be executed against it without the need to
specify the database in the query's execute method.
bind_ctx([database=None])
Parameters
database -- Database object.
Return a context manager that will bind the table to the given database for the duration of
the wrapped block.
select(*columns)
Parameters
columns -- Column instances, expressions, functions, sub-queries, or anything else
that you would like to select.
Create a Select query on the table. If the table explicitly declares columns and no columns
are provided, then by default all the table's defined columns will be selected.
Example:
User = Table('users', ('id', 'username'))
# Because columns were defined on the Table, we will default to
# selecting both of the User table's columns.
# Evaluates to SELECT id, username FROM users
query = User.select()
Note = Table('notes')
query = (Note
.select(Note.c.content, Note.c.timestamp, User.username)
.join(User, on=(Note.c.user_id == User.id))
.where(Note.c.is_published == True)
.order_by(Note.c.timestamp.desc()))
# Using a function to select users and the number of notes they
# have authored.
query = (User
.select(
User.username,
fn.COUNT(Note.c.id).alias('n_notes'))
.join(
Note,
JOIN.LEFT_OUTER,
on=(User.id == Note.c.user_id))
.order_by(fn.COUNT(Note.c.id).desc()))
insert([insert=None[, columns=None[, **kwargs]]])
Parameters
• insert -- A dictionary mapping column to value, an iterable that yields
dictionaries (i.e. list), or a Select query.
• columns (list) -- The list of columns to insert into when the data being inserted
is not a dictionary.
• kwargs -- Mapping of column-name to value.
Create a Insert query into the table.
replace([insert=None[, columns=None[, **kwargs]]])
Parameters
• insert -- A dictionary mapping column to value, an iterable that yields
dictionaries (i.e. list), or a Select query.
• columns (list) -- The list of columns to insert into when the data being inserted
is not a dictionary.
• kwargs -- Mapping of column-name to value.
Create a Insert query into the table whose conflict resolution method is to replace.
update([update=None[, **kwargs]])
Parameters
• update -- A dictionary mapping column to value.
• kwargs -- Mapping of column-name to value.
Create a Update query for the table.
delete()
Create a Delete query for the table.
class Join(lhs, rhs[, join_type=JOIN.INNER[, on=None[, alias=None]]])
Represent a JOIN between to table-like objects.
Parameters
• lhs -- Left-hand side of the join.
• rhs -- Right-hand side of the join.
• join_type -- Type of join. e.g. JOIN.INNER, JOIN.LEFT_OUTER, etc.
• on -- Expression describing the join predicate.
• alias (str) -- Alias to apply to joined data.
on(predicate)
Parameters
predicate (Expression) -- join predicate.
Specify the predicate expression used for this join.
class ValuesList(values[, columns=None[, alias=None]])
Represent a values list that can be used like a table.
Parameters
• values -- a list-of-lists containing the row data to represent.
• columns (list) -- the names to give to the columns in each row.
• alias (str) -- alias to use for values-list.
Example:
data = [(1, 'first'), (2, 'second')]
vl = ValuesList(data, columns=('idx', 'name'))
query = (vl
.select(vl.c.idx, vl.c.name)
.order_by(vl.c.idx))
# Yields:
# SELECT t1.idx, t1.name
# FROM (VALUES (1, 'first'), (2, 'second')) AS t1(idx, name)
# ORDER BY t1.idx
columns(*names)
Parameters
names -- names to apply to the columns of data.
Example:
vl = ValuesList([(1, 'first'), (2, 'second')])
vl = vl.columns('idx', 'name').alias('v')
query = vl.select(vl.c.idx, vl.c.name)
# Yields:
# SELECT v.idx, v.name
# FROM (VALUES (1, 'first'), (2, 'second')) AS v(idx, name)
class CTE(name, query[, recursive=False[, columns=None]])
Represent a common-table-expression. For example queries, see cte.
Parameters
• name -- Name for the CTE.
• query -- Select query describing CTE.
• recursive (bool) -- Whether the CTE is recursive.
• columns (list) -- Explicit list of columns produced by CTE (optional).
select_from(*columns)
Create a SELECT query that utilizes the given common table expression as the source for a
new query.
Parameters
columns -- One or more columns to select from the CTE.
Returns
Select query utilizing the common table expression
union_all(other)
Used on the base-case CTE to construct the recursive term of the CTE.
Parameters
other -- recursive term, generally a Select query.
Returns
a recursive CTE with the given recursive term.
class ColumnBase
Base-class for column-like objects, attributes or expressions.
Column-like objects can be composed using various operators and special methods.
• &: Logical AND
• |: Logical OR
• +: Addition
• -: Subtraction
• *: Multiplication
• /: Division
• ^: Exclusive-OR
• ==: Equality
• !=: Inequality
• >: Greater-than
• <: Less-than
• >=: Greater-than or equal
• <=: Less-than or equal
• <<: IN
• >>: IS (i.e. IS NULL)
• %: LIKE
• **: ILIKE
• bin_and(): Binary AND
• bin_or(): Binary OR
• in_(): IN
• not_in(): NOT IN
• regexp(): REGEXP
• is_null(True/False): IS NULL or IS NOT NULL
• contains(s): LIKE %s%
• startswith(s): LIKE s%
• endswith(s): LIKE %s
• between(low, high): BETWEEN low AND high
• concat(): ||
alias(alias)
Parameters
alias (str) -- Alias for the given column-like object.
Returns
a Alias object.
Indicate the alias that should be given to the specified column-like object.
cast(as_type)
Parameters
as_type (str) -- Type name to cast to.
Returns
a Cast object.
Create a CAST expression.
asc()
Returns
an ascending Ordering object for the column.
desc()
Returns
an descending Ordering object for the column.
__invert__()
Returns
a Negated wrapper for the column.
class Column(source, name)
Parameters
• source (Source) -- Source for column.
• name (str) -- Column name.
Column on a table or a column returned by a sub-query.
class Alias(node, alias)
Parameters
• node (Node) -- a column-like object.
• alias (str) -- alias to assign to column.
Create a named alias for the given column-like object.
alias([alias=None])
Parameters
alias (str) -- new name (or None) for aliased column.
Create a new Alias for the aliased column-like object. If the new alias is None, then the
original column-like object is returned.
class Negated(node)
Represents a negated column-like object.
class Value(value[, converterNone[, unpack=True]])
Parameters
• value -- Python object or scalar value.
• converter -- Function used to convert value into type the database understands.
• unpack (bool) -- Whether lists or tuples should be unpacked into a list of values or
treated as-is.
Value to be used in a parameterized query. It is the responsibility of the caller to ensure that
the value passed in can be adapted to a type the database driver understands.
AsIs(value)
Represents a Value that is treated as-is, and passed directly back to the database driver. This
may be useful if you are using database extensions that accept native Python data-types and you do
not wish Peewee to impose any handling of the values.
class Cast(node, cast)
Parameters
• node -- A column-like object.
• cast (str) -- Type to cast to.
Represents a CAST(<node> AS <cast>) expression.
class Ordering(node, direction[, collation=None[, nulls=None]])
Parameters
• node -- A column-like object.
• direction (str) -- ASC or DESC
• collation (str) -- Collation name to use for sorting.
• nulls (str) -- Sort nulls (FIRST or LAST).
Represent ordering by a column-like object.
collate([collation=None])
Parameters
collation (str) -- Collation name to use for sorting.
Asc(node[, collation=None[, nulls=None]])
Short-hand for instantiating an ascending Ordering object.
Desc(node[, collation=None[, nulls=None]])
Short-hand for instantiating an descending Ordering object.
class Expression(lhs, op, rhs[, flat=True])
Parameters
• lhs -- Left-hand side.
• op -- Operation.
• rhs -- Right-hand side.
• flat (bool) -- Whether to wrap expression in parentheses.
Represent a binary expression of the form (lhs op rhs), e.g. (foo + 1).
class Entity(*path)
Parameters
path -- Components that make up the dotted-path of the entity name.
Represent a quoted entity in a query, such as a table, column, alias. The name may consist of
multiple components, e.g. "a_table"."column_name".
__getattr__(self, attr)
Factory method for creating sub-entities.
class SQL(sql[, params=None])
Parameters
• sql (str) -- SQL query string.
• params (tuple) -- Parameters for query (optional).
Represent a parameterized SQL query or query-fragment.
Check(constraint)
Parameters
constraint (str) -- Constraint SQL.
Represent a CHECK constraint.
class Function(name, arguments[, coerce=True])
Parameters
• name (str) -- Function name.
• arguments (tuple) -- Arguments to function.
• coerce (bool) -- Whether to coerce the function result to a particular data-type when
reading function return values from the cursor.
Represent an arbitrary SQL function call.
NOTE:
Rather than instantiating this class directly, it is recommended to use the fn helper.
Example of using fn to call an arbitrary SQL function:
# Query users and count of tweets authored.
query = (User
.select(User.username, fn.COUNT(Tweet.id).alias('ct'))
.join(Tweet, JOIN.LEFT_OUTER, on=(User.id == Tweet.user_id))
.group_by(User.username)
.order_by(fn.COUNT(Tweet.id).desc()))
over([partition_by=None[, order_by=None[, start=None[, end=None[, window=None]]]]])
Parameters
• partition_by (list) -- List of columns to partition by.
• order_by (list) -- List of columns / expressions to order window by.
• start -- A SQL instance or a string expressing the start of the window range.
• end -- A SQL instance or a string expressing the end of the window range.
• frame_type (str) -- Window.RANGE or Window.ROWS.
• window (Window) -- A Window instance.
NOTE:
For an in-depth guide to using window functions with Peewee, see the window-functions
section.
Examples:
# Using a simple partition on a single column.
query = (Sample
.select(
Sample.counter,
Sample.value,
fn.AVG(Sample.value).over([Sample.counter]))
.order_by(Sample.counter))
# Equivalent example Using a Window() instance instead.
window = Window(partition_by=[Sample.counter])
query = (Sample
.select(
Sample.counter,
Sample.value,
fn.AVG(Sample.value).over(window))
.window(window) # Note call to ".window()"
.order_by(Sample.counter))
# Example using bounded window.
query = (Sample
.select(Sample.value,
fn.SUM(Sample.value).over(
partition_by=[Sample.counter],
start=Window.CURRENT_ROW, # current row
end=Window.following())) # unbounded following
.order_by(Sample.id))
filter(where)
Parameters
where -- Expression for filtering aggregate.
Add a FILTER (WHERE...) clause to an aggregate function. The where expression is evaluated
to determine which rows are fed to the aggregate function. This SQL feature is supported
for Postgres and SQLite.
coerce([coerce=True])
Parameters
coerce (bool) -- Whether to coerce function-call result.
fn() The fn() helper is actually an instance of Function that implements a __getattr__ hook to provide
a nice API for calling SQL functions.
To create a node representative of a SQL function call, use the function name as an attribute on
fn and then provide the arguments as you would if calling a Python function:
# List users and the number of tweets they have authored,
# from highest-to-lowest:
sql_count = fn.COUNT(Tweet.id)
query = (User
.select(User, sql_count.alias('count'))
.join(Tweet, JOIN.LEFT_OUTER)
.group_by(User)
.order_by(sql_count.desc()))
# Get the timestamp of the most recent tweet:
query = Tweet.select(fn.MAX(Tweet.timestamp))
max_timestamp = query.scalar() # Retrieve scalar result from query.
Function calls can, like anything else, be composed and nested:
# Get users whose username begins with "A" or "a":
a_users = User.select().where(fn.LOWER(fn.SUBSTR(User.username, 1, 1)) == 'a')
class Window([partition_by=None[, order_by=None[, start=None[, end=None[, frame_type=None[,
alias=None]]]]]])
Parameters
• partition_by (list) -- List of columns to partition by.
• order_by (list) -- List of columns to order by.
• start -- A SQL instance or a string expressing the start of the window range.
• end -- A SQL instance or a string expressing the end of the window range.
• frame_type (str) -- Window.RANGE or Window.ROWS.
• alias (str) -- Alias for the window.
Represent a WINDOW clause.
NOTE:
For an in-depth guide to using window functions with Peewee, see the window-functions section.
CURRENT_ROW
Reference to current row for use in start/end clause.
RANGE Specify the use of RANGE for the window frame_type. For more information, see
window-frame-types.
ROWS Specify the use of ROWS for the window frame_type. For more information, see
window-frame-types.
static preceding([value=None])
Parameters
value -- Number of rows preceding. If None is UNBOUNDED.
Convenience method for generating SQL suitable for passing in as the start parameter for a
window range.
static following([value=None])
Parameters
value -- Number of rows following. If None is UNBOUNDED.
Convenience method for generating SQL suitable for passing in as the end parameter for a
window range.
alias([alias=None])
Parameters
alias (str) -- Alias to use for window.
Case(predicate, expression_tuples[, default=None]])
Parameters
• predicate -- Predicate for CASE query (optional).
• expression_tuples -- One or more cases to evaluate.
• default -- Default value (optional).
Returns
Representation of CASE statement.
Examples:
Number = Table('numbers', ('val',))
num_as_str = Case(Number.val, (
(1, 'one'),
(2, 'two'),
(3, 'three')), 'a lot')
query = Number.select(Number.val, num_as_str.alias('num_str'))
# The above is equivalent to:
# SELECT "val",
# CASE "val"
# WHEN 1 THEN 'one'
# WHEN 2 THEN 'two'
# WHEN 3 THEN 'three'
# ELSE 'a lot' END AS "num_str"
# FROM "numbers"
num_as_str = Case(None, (
(Number.val == 1, 'one'),
(Number.val == 2, 'two'),
(Number.val == 3, 'three')), 'a lot')
query = Number.select(Number.val, num_as_str.alias('num_str'))
# The above is equivalent to:
# SELECT "val",
# CASE
# WHEN "val" = 1 THEN 'one'
# WHEN "val" = 2 THEN 'two'
# WHEN "val" = 3 THEN 'three'
# ELSE 'a lot' END AS "num_str"
# FROM "numbers"
class NodeList(nodes[, glue=' '[, parens=False]])
Parameters
• nodes (list) -- Zero or more nodes.
• glue (str) -- How to join the nodes when converting to SQL.
• parens (bool) -- Whether to wrap the resulting SQL in parentheses.
Represent a list of nodes, a multi-part clause, a list of parameters, etc.
CommaNodeList(nodes)
Parameters
nodes (list) -- Zero or more nodes.
Returns
a NodeList
Represent a list of nodes joined by commas.
EnclosedNodeList(nodes)
Parameters
nodes (list) -- Zero or more nodes.
Returns
a NodeList
Represent a list of nodes joined by commas and wrapped in parentheses.
class DQ(**query)
Parameters
query -- Arbitrary filter expressions using Django-style lookups.
Represent a composable Django-style filter expression suitable for use with the Model.filter() or
ModelSelect.filter() methods.
class Tuple(*args)
Represent a SQL row tuple.
class OnConflict([action=None[, update=None[, preserve=None[, where=None[, conflict_target=None]]]]])
Parameters
• action (str) -- Action to take when resolving conflict.
• update -- A dictionary mapping column to new value.
• preserve -- A list of columns whose values should be preserved from the original INSERT.
• where -- Expression to restrict the conflict resolution.
• conflict_target -- Name of column or constraint to check.
Represent a conflict resolution clause for a data-modification query.
Depending on the database-driver being used, one or more of the above parameters may be required.
preserve(*columns)
Parameters
columns -- Columns whose values should be preserved.
update([_data=None[, **kwargs]])
Parameters
• _data (dict) -- Dictionary mapping column to new value.
• kwargs -- Dictionary mapping column name to new value.
The update() method supports being called with either a dictionary of column-to-value, or
keyword arguments representing the same.
where(*expressions)
Parameters
expressions -- Expressions that restrict the action of the conflict resolution
clause.
conflict_target(*constraints)
Parameters
constraints -- Name(s) of columns/constraints that are the target of the conflict
resolution.
class BaseQuery
The parent class from which all other query classes are derived. While you will not deal with
BaseQuery directly in your code, it implements some methods that are common across all query
types.
default_row_type = ROW.DICT
bind([database=None])
Parameters
database (Database) -- Database to execute query against.
Bind the query to the given database for execution.
dicts([as_dict=True])
Parameters
as_dict (bool) -- Specify whether to return rows as dictionaries.
Return rows as dictionaries.
tuples([as_tuples=True])
Parameters
as_tuple (bool) -- Specify whether to return rows as tuples.
Return rows as tuples.
namedtuples([as_namedtuple=True])
Parameters
as_namedtuple (bool) -- Specify whether to return rows as named tuples.
Return rows as named tuples.
objects([constructor=None])
Parameters
constructor -- Function that accepts row dict and returns an arbitrary object.
Return rows as arbitrary objects using the given constructor.
sql()
Returns
A 2-tuple consisting of the query's SQL and parameters.
execute(database)
Parameters
database (Database) -- Database to execute query against. Not required if query was
previously bound to a database.
Execute the query and return result (depends on type of query being executed). For example,
select queries the return result will be an iterator over the query results.
iterator([database=None])
Parameters
database (Database) -- Database to execute query against. Not required if query was
previously bound to a database.
Execute the query and return an iterator over the result-set. For large result-sets this
method is preferable as rows are not cached in-memory during iteration.
NOTE:
Because rows are not cached, the query may only be iterated over once. Subsequent
iterations will return empty result-sets as the cursor will have been consumed.
Example:
query = StatTbl.select().order_by(StatTbl.timestamp).tuples()
for row in query.iterator(db):
process_row(row)
__iter__()
Execute the query and return an iterator over the result-set.
Unlike iterator(), this method will cause rows to be cached in order to allow efficient
iteration, indexing and slicing.
__getitem__(value)
Parameters
value -- Either an integer index or a slice.
Retrieve a row or range of rows from the result-set.
__len__()
Return the number of rows in the result-set.
WARNING:
This does not issue a COUNT() query. Instead, the result-set is loaded as it would be
during normal iteration, and the length is determined from the size of the result set.
class RawQuery([sql=None[, params=None[, **kwargs]]])
Parameters
• sql (str) -- SQL query.
• params (tuple) -- Parameters (optional).
Create a query by directly specifying the SQL to execute.
class Query([where=None[, order_by=None[, limit=None[, offset=None[, **kwargs]]]]])
Parameters
• where -- Representation of WHERE clause.
• order_by (tuple) -- Columns or values to order by.
• limit (int) -- Value of LIMIT clause.
• offset (int) -- Value of OFFSET clause.
Base-class for queries that support method-chaining APIs.
with_cte(*cte_list)
Parameters
cte_list -- zero or more CTE objects.
Include the given common-table expressions in the query. Any previously specified CTEs will
be overwritten. For examples of common-table expressions, see cte.
where(*expressions)
Parameters
expressions -- zero or more expressions to include in the WHERE clause.
Include the given expressions in the WHERE clause of the query. The expressions will be
AND-ed together with any previously-specified WHERE expressions.
Example selection users where the username is equal to 'somebody':
sq = User.select().where(User.username == 'somebody')
Example selecting tweets made by users who are either editors or administrators:
sq = Tweet.select().join(User).where(
(User.is_editor == True) |
(User.is_admin == True))
Example of deleting tweets by users who are no longer active:
inactive_users = User.select().where(User.active == False)
dq = (Tweet
.delete()
.where(Tweet.user.in_(inactive_users)))
dq.execute() # Return number of tweets deleted.
NOTE:
where() calls are chainable. Multiple calls will be "AND"-ed together.
order_by(*values)
Parameters
values -- zero or more Column-like objects to order by.
Define the ORDER BY clause. Any previously-specified values will be overwritten.
order_by_extend(*values)
Parameters
values -- zero or more Column-like objects to order by.
Extend any previously-specified ORDER BY clause with the given values.
limit([value=None])
Parameters
value (int) -- specify value for LIMIT clause.
offset([value=None])
Parameters
value (int) -- specify value for OFFSET clause.
paginate(page[, paginate_by=20])
Parameters
• page (int) -- Page number of results (starting from 1).
• paginate_by (int) -- Rows-per-page.
Convenience method for specifying the LIMIT and OFFSET in a more intuitive way.
This feature is designed with web-site pagination in mind, so the first page starts with
page=1.
class SelectQuery
Select query helper-class that implements operator-overloads for creating compound queries.
cte(name[, recursive=False[, columns=None]])
Parameters
• name (str) -- Alias for common table expression.
• recursive (bool) -- Will this be a recursive CTE?
• columns (list) -- List of column names (as strings).
Indicate that a query will be used as a common table expression. For example, if we are
modelling a category tree and are using a parent-link foreign key, we can retrieve all
categories and their absolute depths using a recursive CTE:
class Category(Model):
name = TextField()
parent = ForeignKeyField('self', backref='children', null=True)
# The base case of our recursive CTE will be categories that are at
# the root level -- in other words, categories without parents.
roots = (Category
.select(Category.name, Value(0).alias('level'))
.where(Category.parent.is_null())
.cte(name='roots', recursive=True))
# The recursive term will select the category name and increment
# the depth, joining on the base term so that the recursive term
# consists of all children of the base category.
RTerm = Category.alias()
recursive = (RTerm
.select(RTerm.name, (roots.c.level + 1).alias('level'))
.join(roots, on=(RTerm.parent == roots.c.id)))
# Express <base term> UNION ALL <recursive term>.
cte = roots.union_all(recursive)
# Select name and level from the recursive CTE.
query = (cte
.select_from(cte.c.name, cte.c.level)
.order_by(cte.c.name))
for category in query:
print(category.name, category.level)
For more examples of CTEs, see cte.
union_all(dest)
Create a UNION ALL query with dest.
__add__(dest)
Create a UNION ALL query with dest.
union(dest)
Create a UNION query with dest.
__or__(dest)
Create a UNION query with dest.
intersect(dest)
Create an INTERSECT query with dest.
__and__(dest)
Create an INTERSECT query with dest.
except_(dest)
Create an EXCEPT query with dest. Note that the method name has a trailing "_" character
since except is a Python reserved word.
__sub__(dest)
Create an EXCEPT query with dest.
class SelectBase
Base-class for Select and CompoundSelect queries.
peek(database[, n=1])
Parameters
• database (Database) -- database to execute query against.
• n (int) -- Number of rows to return.
Returns
A single row if n = 1, else a list of rows.
Execute the query and return the given number of rows from the start of the cursor. This
function may be called multiple times safely, and will always return the first N rows of
results.
first(database[, n=1])
Parameters
• database (Database) -- database to execute query against.
• n (int) -- Number of rows to return.
Returns
A single row if n = 1, else a list of rows.
Like the peek() method, except a LIMIT is applied to the query to ensure that only n rows
are returned. Multiple calls for the same value of n will not result in multiple
executions.
scalar(database[, as_tuple=False])
Parameters
• database (Database) -- database to execute query against.
• as_tuple (bool) -- Return the result as a tuple?
Returns
Single scalar value if as_tuple = False, else row tuple.
Return a scalar value from the first row of results. If multiple scalar values are
anticipated (e.g. multiple aggregations in a single query) then you may specify
as_tuple=True to get the row tuple.
Example:
query = Note.select(fn.MAX(Note.timestamp))
max_ts = query.scalar(db)
query = Note.select(fn.MAX(Note.timestamp), fn.COUNT(Note.id))
max_ts, n_notes = query.scalar(db, as_tuple=True)
count(database[, clear_limit=False])
Parameters
• database (Database) -- database to execute query against.
• clear_limit (bool) -- Clear any LIMIT clause when counting.
Returns
Number of rows in the query result-set.
Return number of rows in the query result-set.
Implemented by running SELECT COUNT(1) FROM (<current query>).
exists(database)
Parameters
database (Database) -- database to execute query against.
Returns
Whether any results exist for the current query.
Return a boolean indicating whether the current query has any results.
get(database)
Parameters
database (Database) -- database to execute query against.
Returns
A single row from the database or None.
Execute the query and return the first row, if it exists. Multiple calls will result in
multiple queries being executed.
class CompoundSelectQuery(lhs, op, rhs)
Parameters
• lhs (SelectBase) -- A Select or CompoundSelect query.
• op (str) -- Operation (e.g. UNION, INTERSECT, EXCEPT).
• rhs (SelectBase) -- A Select or CompoundSelect query.
Class representing a compound SELECT query.
class Select([from_list=None[, columns=None[, group_by=None[, having=None[, distinct=None[,
windows=None[, for_update=None[, **kwargs]]]]]]]])
Parameters
• from_list (list) -- List of sources for FROM clause.
• columns (list) -- Columns or values to select.
• group_by (list) -- List of columns or values to group by.
• having (Expression) -- Expression for HAVING clause.
• distinct -- Either a boolean or a list of column-like objects.
• windows (list) -- List of Window clauses.
• for_update -- Boolean or str indicating if SELECT...FOR UPDATE.
Class representing a SELECT query.
NOTE:
Rather than instantiating this directly, most-commonly you will use a factory method like
Table.select() or Model.select().
Methods on the select query can be chained together.
Example selecting some user instances from the database. Only the id and username columns are
selected. When iterated, will return instances of the User model:
query = User.select(User.id, User.username)
for user in query:
print(user.username)
Example selecting users and additionally the number of tweets made by the user. The User
instances returned will have an additional attribute, 'count', that corresponds to the number of
tweets made:
query = (User
.select(User, fn.COUNT(Tweet.id).alias('count'))
.join(Tweet, JOIN.LEFT_OUTER)
.group_by(User))
for user in query:
print(user.username, 'has tweeted', user.count, 'times')
NOTE:
While it is possible to instantiate Select directly, more commonly you will build the query
using the method-chaining APIs.
columns(*columns)
Parameters
columns -- Zero or more column-like objects to SELECT.
Specify which columns or column-like values to SELECT.
select(*columns)
Parameters
columns -- Zero or more column-like objects to SELECT.
Same as Select.columns(), provided for backwards-compatibility.
select_extend(*columns)
Parameters
columns -- Zero or more column-like objects to SELECT.
Extend the current selection with the given columns.
Example:
def get_users(with_count=False):
query = User.select()
if with_count:
query = (query
.select_extend(fn.COUNT(Tweet.id).alias('count'))
.join(Tweet, JOIN.LEFT_OUTER)
.group_by(User))
return query
from_(*sources)
Parameters
sources -- Zero or more sources for the FROM clause.
Specify which table-like objects should be used in the FROM clause.
User = Table('users')
Tweet = Table('tweets')
query = (User
.select(User.c.username, Tweet.c.content)
.from_(User, Tweet)
.where(User.c.id == Tweet.c.user_id))
for row in query.execute(db):
print(row['username'], '->', row['content'])
join(dest[, join_type='INNER'[, on=None]])
Parameters
• dest -- A table or table-like object.
• join_type (str) -- Type of JOIN, default is "INNER".
• on (Expression) -- Join predicate.
Join type may be one of:
• JOIN.INNER
• JOIN.LEFT_OUTER
• JOIN.RIGHT_OUTER
• JOIN.FULL
• JOIN.FULL_OUTER
• JOIN.CROSS
Express a JOIN:
User = Table('users', ('id', 'username'))
Note = Table('notes', ('id', 'user_id', 'content'))
query = (Note
.select(Note.content, User.username)
.join(User, on=(Note.user_id == User.id)))
group_by(*columns)
Parameters
values -- zero or more Column-like objects to group by.
Define the GROUP BY clause. Any previously-specified values will be overwritten.
Additionally, to specify all columns on a given table, you can pass the table/model object
in place of the individual columns.
Example:
query = (User
.select(User, fn.Count(Tweet.id).alias('count'))
.join(Tweet)
.group_by(User))
group_by_extend(*columns)
Parameters
values -- zero or more Column-like objects to group by.
Extend the GROUP BY clause with the given columns.
having(*expressions)
Parameters
expressions -- zero or more expressions to include in the HAVING clause.
Include the given expressions in the HAVING clause of the query. The expressions will be
AND-ed together with any previously-specified HAVING expressions.
distinct(*columns)
Parameters
columns -- Zero or more column-like objects.
Indicate whether this query should use a DISTINCT clause. By specifying a single value of
True the query will use a simple SELECT DISTINCT. Specifying one or more columns will
result in a SELECT DISTINCT ON.
window(*windows)
Parameters
windows -- zero or more Window objects.
Define the WINDOW clause. Any previously-specified values will be overwritten.
Example:
# Equivalent example Using a Window() instance instead.
window = Window(partition_by=[Sample.counter])
query = (Sample
.select(
Sample.counter,
Sample.value,
fn.AVG(Sample.value).over(window))
.window(window) # Note call to ".window()"
.order_by(Sample.counter))
for_update([for_update=True])
Parameters
for_update -- Either a boolean or a string indicating the desired expression, e.g.
"FOR UPDATE NOWAIT".
class _WriteQuery(table[, returning=None[, **kwargs]])
Parameters
• table (Table) -- Table to write to.
• returning (list) -- List of columns for RETURNING clause.
Base-class for write queries.
returning(*returning)
Parameters
returning -- Zero or more column-like objects for RETURNING clause
Specify the RETURNING clause of query (if supported by your database).
query = (User
.insert_many([{'username': 'foo'},
{'username': 'bar'},
{'username': 'baz'}])
.returning(User.id, User.username)
.namedtuples())
data = query.execute()
for row in data:
print('added:', row.username, 'with id=', row.id)
class Update(table[, update=None[, **kwargs]])
Parameters
• table (Table) -- Table to update.
• update (dict) -- Data to update.
Class representing an UPDATE query.
Example:
PageView = Table('page_views')
query = (PageView
.update({PageView.c.page_views: PageView.c.page_views + 1})
.where(PageView.c.url == url))
query.execute(database)
from_(*sources)
Parameters
sources (Source) -- one or more Table, Model, query, or ValuesList to join with.
Specify additional tables to join with using the UPDATE ... FROM syntax, which is supported
by Postgres. The Postgres documentation provides additional detail, but to summarize:
When a FROM clause is present, what essentially happens is that the target table is
joined to the tables mentioned in the from_list, and each output row of the join
represents an update operation for the target table. When using FROM you should ensure
that the join produces at most one output row for each row to be modified.
Example:
# Update multiple users in a single query.
data = [('huey', True),
('mickey', False),
('zaizee', True)]
vl = ValuesList(data, columns=('username', 'is_admin'), alias='vl')
# Here we'll update the "is_admin" status of the above users,
# "joining" the VALUES() on the "username" column.
query = (User
.update(is_admin=QualifiedNames(vl.c.is_admin))
.from_(vl)
.where(QualifiedNames(User.username == vl.c.username)))
The above query produces the following SQL:
UPDATE "users" SET "is_admin" = "vl"."is_admin"
FROM (
VALUES ('huey', t), ('mickey', f), ('zaizee', t))
AS "vl"("username", "is_admin")
WHERE ("users"."username" = "vl"."username")
NOTE:
Note the usage of QualifiedNames, which wraps the "is_admin" value in the assignment
portion of the query, and which wraps both tables in the join condition. Ordinarily,
fully-qualified names are not supported in UPDATE queries, so we must explicitly tell
Peewee that we wish to use qualified names when using the UPDATE ... FROM syntax.
class Insert(table[, insert=None[, columns=None[, on_conflict=None[, **kwargs]]]])
Parameters
• table (Table) -- Table to INSERT data into.
• insert -- Either a dict, a list, or a query.
• columns (list) -- List of columns when insert is a list or query.
• on_conflict -- Conflict resolution strategy.
Class representing an INSERT query.
on_conflict_ignore([ignore=True])
Parameters
ignore (bool) -- Whether to add ON CONFLICT IGNORE clause.
Specify IGNORE conflict resolution strategy.
on_conflict_replace([replace=True])
Parameters
ignore (bool) -- Whether to add ON CONFLICT REPLACE clause.
Specify REPLACE conflict resolution strategy.
on_conflict([action=None[, update=None[, preserve=None[, where=None[, conflict_target=None]]]]])
Parameters
• action (str) -- Action to take when resolving conflict. If blank, action is
assumed to be "update".
• update -- A dictionary mapping column to new value.
• preserve -- A list of columns whose values should be preserved from the original
INSERT.
• where -- Expression to restrict the conflict resolution.
• conflict_target -- Name of column or constraint to check.
Specify the parameters for an OnConflict clause to use for conflict resolution.
Example:
class User(Model):
username = TextField(unique=True)
last_login = DateTimeField(null=True)
login_count = IntegerField()
def log_user_in(username):
now = datetime.datetime.now()
# INSERT a new row for the user with the current timestamp and
# login count set to 1. If the user already exists, then we
# will preserve the last_login value from the "insert()" clause
# and atomically increment the login-count.
userid = (User
.insert(username=username, last_login=now, login_count=1)
.on_conflict(
conflict_target=[User.username],
preserve=[User.last_login],
update={User.login_count: User.login_count + 1})
.execute())
return userid
class Delete
Class representing a DELETE query.
class Index(name, table, expressions[, unique=False[, safe=False[, where=None[, using=None]]]])
Parameters
• name (str) -- Index name.
• table (Table) -- Table to create index on.
• expressions -- List of columns to index on (or expressions).
• unique (bool) -- Whether index is UNIQUE.
• safe (bool) -- Whether to add IF NOT EXISTS clause.
• where (Expression) -- Optional WHERE clause for index.
• using (str) -- Index algorithm.
safe([_safe=True])
Parameters
_safe (bool) -- Whether to add IF NOT EXISTS clause.
where(*expressions)
Parameters
expressions -- zero or more expressions to include in the WHERE clause.
Include the given expressions in the WHERE clause of the index. The expressions will be
AND-ed together with any previously-specified WHERE expressions.
using([_using=None])
Parameters
_using (str) -- Specify index algorithm for USING clause.
class ModelIndex(model, fields[, unique=False[, safe=True[, where=None[, using=None[, name=None]]]]])
Parameters
• model (Model) -- Model class to create index on.
• fields (list) -- Fields to index.
• unique (bool) -- Whether index is UNIQUE.
• safe (bool) -- Whether to add IF NOT EXISTS clause.
• where (Expression) -- Optional WHERE clause for index.
• using (str) -- Index algorithm.
• name (str) -- Optional index name.
Expressive method for declaring an index on a model.
Examples:
class Article(Model):
name = TextField()
timestamp = TimestampField()
status = IntegerField()
flags = BitField()
is_sticky = flags.flag(1)
is_favorite = flags.flag(2)
# CREATE INDEX ... ON "article" ("name", "timestamp")
idx = ModelIndex(Article, (Article.name, Article.timestamp))
# CREATE INDEX ... ON "article" ("name", "timestamp") WHERE "status" = 1
idx = idx.where(Article.status == 1)
# CREATE UNIQUE INDEX ... ON "article" ("timestamp" DESC, "flags" & 2) WHERE "status" = 1
idx = ModelIndex(
Article,
(Article.timestamp.desc(), Article.flags.bin_and(2)),
unique = True).where(Article.status == 1)
You can also use Model.index():
idx = Article.index(Article.name, Article.timestamp).where(Article.status == 1)
To add an index to a model definition use Model.add_index():
idx = Article.index(Article.name, Article.timestamp).where(Article.status == 1)
# Add above index definition to the model definition. When you call
# Article.create_table() (or database.create_tables([Article])), the
# index will be created.
Article.add_index(idx)
Fields
class Field([null=False[, index=False[, unique=False[, column_name=None[, default=None[,
primary_key=False[, constraints=None[, sequence=None[, collation=None[, unindexed=False[, choices=None[,
help_text=None[, verbose_name=None]]]]]]]]]]]]])
Parameters
• null (bool) -- Field allows NULLs.
• index (bool) -- Create an index on field.
• unique (bool) -- Create a unique index on field.
• column_name (str) -- Specify column name for field.
• default -- Default value (enforced in Python, not on server).
• primary_key (bool) -- Field is the primary key.
• constraints (list) -- List of constraints to apply to column, for example: [Check('price
> 0')].
• sequence (str) -- Sequence name for field.
• collation (str) -- Collation name for field.
• unindexed (bool) -- Declare field UNINDEXED (sqlite only).
• choices (list) -- An iterable of 2-tuples mapping column values to display labels. Used
for metadata purposes only, to help when displaying a dropdown of choices for field
values, for example.
• help_text (str) -- Help-text for field, metadata purposes only.
• verbose_name (str) -- Verbose name for field, metadata purposes only.
Fields on a Model are analogous to columns on a table.
field_type = '<some field type>'
Attribute used to map this field to a column type, e.g. "INT". See the FIELD object in the
source for more information.
column Retrieve a reference to the underlying Column object.
model The model the field is bound to.
name The name of the field.
db_value(value)
Coerce a Python value into a value suitable for storage in the database. Sub-classes
operating on special data-types will most likely want to override this method.
python_value(value)
Coerce a value from the database into a Python object. Sub-classes operating on special
data-types will most likely want to override this method.
coerce(value)
This method is a shorthand that is used, by default, by both db_value() and python_value().
Parameters
value -- arbitrary data from app or backend
Return type
python data type
class IntegerField
Field class for storing integers.
class BigIntegerField
Field class for storing big integers (if supported by database).
class SmallIntegerField
Field class for storing small integers (if supported by database).
class AutoField
Field class for storing auto-incrementing primary keys.
NOTE:
In SQLite, for performance reasons, the default primary key type simply uses the max existing
value + 1 for new values, as opposed to the max ever value + 1. This means deleted records can
have their primary keys reused. In conjunction with SQLite having foreign keys disabled by
default (meaning ON DELETE is ignored, even if you specify it explicitly), this can lead to
surprising and dangerous behaviour. To avoid this, you may want to use one or both of
AutoIncrementField and pragmas=[('foreign_keys', 'on')] when you instantiate SqliteDatabase.
class BigAutoField
Field class for storing auto-incrementing primary keys using 64-bits.
class IdentityField
Field class for storing auto-incrementing primary keys using the new Postgres 10 IDENTITY column
type. The column definition ends up looking like this:
id = IdentityField()
# "id" INT GENERATED BY DEFAULT AS IDENTITY NOT NULL PRIMARY KEY
ATTENTION:
Only supported by Postgres 10.0 and newer.
class FloatField
Field class for storing floating-point numbers.
class DoubleField
Field class for storing double-precision floating-point numbers.
class DecimalField([max_digits=10[, decimal_places=5[, auto_round=False[, rounding=None[, **kwargs]]]]])
Parameters
• max_digits (int) -- Maximum digits to store.
• decimal_places (int) -- Maximum precision.
• auto_round (bool) -- Automatically round values.
• rounding --
Defaults to decimal.DefaultContext.rounding.
Field class for storing decimal numbers. Values are represented as decimal.Decimal
objects.
class CharField([max_length=255])
Field class for storing strings.
NOTE:
Values that exceed length are not truncated automatically.
class FixedCharField
Field class for storing fixed-length strings.
NOTE:
Values that exceed length are not truncated automatically.
class TextField
Field class for storing text.
class BlobField
Field class for storing binary data.
class BitField
Field class for storing options in a 64-bit integer column.
Usage:
class Post(Model):
content = TextField()
flags = BitField()
is_favorite = flags.flag(1)
is_sticky = flags.flag(2)
is_minimized = flags.flag(4)
is_deleted = flags.flag(8)
>>> p = Post()
>>> p.is_sticky = True
>>> p.is_minimized = True
>>> print(p.flags) # Prints 4 | 2 --> "6"
6
>>> p.is_favorite
False
>>> p.is_sticky
True
We can use the flags on the Post class to build expressions in queries as well:
# Generates a WHERE clause that looks like:
# WHERE (post.flags & 1 != 0)
query = Post.select().where(Post.is_favorite)
# Query for sticky + favorite posts:
query = Post.select().where(Post.is_sticky & Post.is_favorite)
flag([value=None])
Parameters
value (int) -- Value associated with flag, typically a power of 2.
Returns a descriptor that can get or set specific bits in the overall value. When accessed
on the class itself, it returns a Expression object suitable for use in a query.
If the value is not provided, it is assumed that each flag will be an increasing power of
2, so if you had four flags, they would have the values 1, 2, 4, 8.
class BigBitField
Field class for storing arbitrarily-large bitmaps in a BLOB. The field will grow the underlying
buffer as necessary, ensuring there are enough bytes of data to support the number of bits of data
being stored.
Example usage:
class Bitmap(Model):
data = BigBitField()
bitmap = Bitmap()
# Sets the ith bit, e.g. the 1st bit, the 11th bit, the 63rd, etc.
bits_to_set = (1, 11, 63, 31, 55, 48, 100, 99)
for bit_idx in bits_to_set:
bitmap.data.set_bit(bit_idx)
# We can test whether a bit is set using "is_set":
assert bitmap.data.is_set(11)
assert not bitmap.data.is_set(12)
# We can clear a bit:
bitmap.data.clear_bit(11)
assert not bitmap.data.is_set(11)
# We can also "toggle" a bit. Recall that the 63rd bit was set earlier.
assert bitmap.data.toggle_bit(63) is False
assert bitmap.data.toggle_bit(63) is True
assert bitmap.data.is_set(63)
set_bit(idx)
Parameters
idx (int) -- Bit to set, indexed starting from zero.
Sets the idx-th bit in the bitmap.
clear_bit(idx)
Parameters
idx (int) -- Bit to clear, indexed starting from zero.
Clears the idx-th bit in the bitmap.
toggle_bit(idx)
Parameters
idx (int) -- Bit to toggle, indexed starting from zero.
Returns
Whether the bit is set or not.
Toggles the idx-th bit in the bitmap and returns whether the bit is set or not.
Example:
>>> bitmap = Bitmap()
>>> bitmap.data.toggle_bit(10) # Toggle the 10th bit.
True
>>> bitmap.data.toggle_bit(10) # This will clear the 10th bit.
False
is_set(idx)
Parameters
idx (int) -- Bit index, indexed starting from zero.
Returns
Whether the bit is set or not.
Returns boolean indicating whether the idx-th bit is set or not.
class UUIDField
Field class for storing uuid.UUID objects. With Postgres, the underlying column's data-type will
be UUID. Since SQLite and MySQL do not have a native UUID type, the UUID is stored as a VARCHAR
instead.
class BinaryUUIDField
Field class for storing uuid.UUID objects efficiently in 16-bytes. Uses the database's BLOB
data-type (or VARBINARY in MySQL, or BYTEA in Postgres).
class DateTimeField([formats=None[, **kwargs]])
Parameters
formats (list) -- A list of format strings to use when coercing a string to a date-time.
Field class for storing datetime.datetime objects.
Accepts a special parameter formats, which contains a list of formats the datetime can be encoded
with (for databases that do not have support for a native datetime data-type). The default
supported formats are:
'%Y-%m-%d %H:%M:%S.%f' # year-month-day hour-minute-second.microsecond
'%Y-%m-%d %H:%M:%S' # year-month-day hour-minute-second
'%Y-%m-%d' # year-month-day
NOTE:
SQLite does not have a native datetime data-type, so datetimes are stored as strings. This is
handled transparently by Peewee, but if you have pre-existing data you should ensure it is
stored as YYYY-mm-dd HH:MM:SS or one of the other supported formats.
year Reference the year of the value stored in the column in a query.
Blog.select().where(Blog.pub_date.year == 2018)
month Reference the month of the value stored in the column in a query.
day Reference the day of the value stored in the column in a query.
hour Reference the hour of the value stored in the column in a query.
minute Reference the minute of the value stored in the column in a query.
second Reference the second of the value stored in the column in a query.
class DateField([formats=None[, **kwargs]])
Parameters
formats (list) -- A list of format strings to use when coercing a string to a date.
Field class for storing datetime.date objects.
Accepts a special parameter formats, which contains a list of formats the datetime can be encoded
with (for databases that do not have support for a native date data-type). The default supported
formats are:
'%Y-%m-%d' # year-month-day
'%Y-%m-%d %H:%M:%S' # year-month-day hour-minute-second
'%Y-%m-%d %H:%M:%S.%f' # year-month-day hour-minute-second.microsecond
NOTE:
If the incoming value does not match a format, it is returned as-is.
year Reference the year of the value stored in the column in a query.
Person.select().where(Person.dob.year == 1983)
month Reference the month of the value stored in the column in a query.
day Reference the day of the value stored in the column in a query.
class TimeField([formats=None[, **kwargs]])
Parameters
formats (list) -- A list of format strings to use when coercing a string to a time.
Field class for storing datetime.time objects (not timedelta).
Accepts a special parameter formats, which contains a list of formats the datetime can be encoded
with (for databases that do not have support for a native time data-type). The default supported
formats are:
'%H:%M:%S.%f' # hour:minute:second.microsecond
'%H:%M:%S' # hour:minute:second
'%H:%M' # hour:minute
'%Y-%m-%d %H:%M:%S.%f' # year-month-day hour-minute-second.microsecond
'%Y-%m-%d %H:%M:%S' # year-month-day hour-minute-second
NOTE:
If the incoming value does not match a format, it is returned as-is.
hour Reference the hour of the value stored in the column in a query.
evening_events = Event.select().where(Event.time.hour > 17)
minute Reference the minute of the value stored in the column in a query.
second Reference the second of the value stored in the column in a query.
class TimestampField([resolution=1[, utc=False[, **kwargs]]])
Parameters
• resolution -- A power of 10, 1=second, 1000=ms, 1000000=us, etc.
• utc (bool) -- Treat timestamps as UTC.
Field class for storing date-times as integer timestamps. Sub-second resolution is supported by
multiplying by a power of 10 to get an integer.
Accepts a special parameter resolution, which is a power-of-10 up to 10^6. This allows sub-second
precision while still using an IntegerField for storage. Default is 1 (second precision).
Also accepts a boolean parameter utc, used to indicate whether the timestamps should be UTC.
Default is False.
Finally, the field default is the current timestamp. If you do not want this behavior, then
explicitly pass in default=None.
class IPField
Field class for storing IPv4 addresses efficiently (as integers).
class BooleanField
Field class for storing boolean values.
class BareField([coerce=None[, **kwargs]])
Parameters
coerce -- Optional function to use for converting raw values into a specific format.
Field class that does not specify a data-type (SQLite-only).
Since data-types are not enforced, you can declare fields without any data-type. It is also common
for SQLite virtual tables to use meta-columns or untyped columns, so for those cases as well you
may wish to use an untyped field.
Accepts a special coerce parameter, a function that takes a value coming from the database and
converts it into the appropriate Python type.
class ForeignKeyField(model[, field=None[, backref=None[, on_delete=None[, on_update=None[,
deferrable=None[, object_id_name=None[, **kwargs]]]]]]])
Parameters
• model (Model) -- Model to reference or the string 'self' if declaring a self-referential
foreign key.
• field (Field) -- Field to reference on model (default is primary key).
• backref (str) -- Accessor name for back-reference.
• on_delete (str) -- ON DELETE action, e.g. 'CASCADE'..
• on_update (str) -- ON UPDATE action.
• deferrable (str) -- Control when constraint is enforced, e.g. 'INITIALLY DEFERRED'.
• object_id_name (str) -- Name for object-id accessor.
Field class for storing a foreign key.
class User(Model):
name = TextField()
class Tweet(Model):
user = ForeignKeyField(User, backref='tweets')
content = TextField()
# "user" attribute
>>> some_tweet.user
<User: charlie>
# "tweets" backref attribute
>>> for tweet in charlie.tweets:
... print(tweet.content)
Some tweet
Another tweet
Yet another tweet
For an in-depth discussion of foreign-keys, joins and relationships between models, refer to
relationships.
NOTE:
Foreign keys do not have a particular field_type as they will take their field type depending
on the type of primary key on the model they are related to.
NOTE:
If you manually specify a field, that field must be either a primary key or have a unique
constraint.
NOTE:
Take care with foreign keys in SQLite. By default, ON DELETE has no effect, which can have
surprising (and usually unwanted) effects on your database integrity. This can affect you even
if you don't specify on_delete, since the default ON DELETE behaviour (to fail without
modifying your data) does not happen, and your data can be silently relinked. The safest thing
to do is to specify pragmas={'foreign_keys': 1} when you instantiate SqliteDatabase.
class DeferredForeignKey(rel_model_name[, **kwargs])
Parameters
rel_model_name (str) -- Model name to reference.
Field class for representing a deferred foreign key. Useful for circular foreign-key references,
for example:
class Husband(Model):
name = TextField()
wife = DeferredForeignKey('Wife', deferrable='INITIALLY DEFERRED')
class Wife(Model):
name = TextField()
husband = ForeignKeyField(Husband, deferrable='INITIALLY DEFERRED')
In the above example, when the Wife model is declared, the foreign-key Husband.wife is
automatically resolved and turned into a regular ForeignKeyField.
class ManyToManyField(model[, backref=None[, through_model=None]])
Parameters
• model (Model) -- Model to create relationship with.
• backref (str) -- Accessor name for back-reference
• through_model (Model) -- Model to use for the intermediary table. If not provided, a
simple through table will be automatically created.
The ManyToManyField provides a simple interface for working with many-to-many relationships,
inspired by Django. A many-to-many relationship is typically implemented by creating a junction
table with foreign keys to the two models being related. For instance, if you were building a
syllabus manager for college students, the relationship between students and courses would be
many-to-many. Here is the schema using standard APIs:
ATTENTION:
This is not a field in the sense that there is no column associated with it. Rather, it
provides a convenient interface for accessing rows of data related via a through model.
Standard way of declaring a many-to-many relationship (without the use of the ManyToManyField):
class Student(Model):
name = CharField()
class Course(Model):
name = CharField()
class StudentCourse(Model):
student = ForeignKeyField(Student)
course = ForeignKeyField(Course)
To query the courses for a particular student, you would join through the junction table:
# List the courses that "Huey" is enrolled in:
courses = (Course
.select()
.join(StudentCourse)
.join(Student)
.where(Student.name == 'Huey'))
for course in courses:
print(course.name)
The ManyToManyField is designed to simplify this use-case by providing a field-like API for
querying and modifying data in the junction table. Here is how our code looks using
ManyToManyField:
class Student(Model):
name = CharField()
class Course(Model):
name = CharField()
students = ManyToManyField(Student, backref='courses')
NOTE:
It does not matter from Peewee's perspective which model the ManyToManyField goes on, since the
back-reference is just the mirror image. In order to write valid Python, though, you will need
to add the ManyToManyField on the second model so that the name of the first model is in the
scope.
We still need a junction table to store the relationships between students and courses. This model
can be accessed by calling the get_through_model() method. This is useful when creating tables.
# Create tables for the students, courses, and relationships between
# the two.
db.create_tables([
Student,
Course,
Course.students.get_through_model()])
When accessed from a model instance, the ManyToManyField exposes a ModelSelect representing the
set of related objects. Let's use the interactive shell to see how all this works:
>>> huey = Student.get(Student.name == 'huey')
>>> [course.name for course in huey.courses]
['English 101', 'CS 101']
>>> engl_101 = Course.get(Course.name == 'English 101')
>>> [student.name for student in engl_101.students]
['Huey', 'Mickey', 'Zaizee']
To add new relationships between objects, you can either assign the objects directly to the
ManyToManyField attribute, or call the add() method. The difference between the two is that simply
assigning will clear out any existing relationships, whereas add() can preserve existing
relationships.
>>> huey.courses = Course.select().where(Course.name.contains('english'))
>>> for course in huey.courses.order_by(Course.name):
... print course.name
English 101
English 151
English 201
English 221
>>> cs_101 = Course.get(Course.name == 'CS 101')
>>> cs_151 = Course.get(Course.name == 'CS 151')
>>> huey.courses.add([cs_101, cs_151])
>>> [course.name for course in huey.courses.order_by(Course.name)]
['CS 101', 'CS151', 'English 101', 'English 151', 'English 201',
'English 221']
This is quite a few courses, so let's remove the 200-level english courses. To remove objects,
use the remove() method.
>>> huey.courses.remove(Course.select().where(Course.name.contains('2'))
2
>>> [course.name for course in huey.courses.order_by(Course.name)]
['CS 101', 'CS151', 'English 101', 'English 151']
To remove all relationships from a collection, you can use the clear() method. Let's say that
English 101 is canceled, so we need to remove all the students from it:
>>> engl_101 = Course.get(Course.name == 'English 101')
>>> engl_101.students.clear()
NOTE:
For an overview of implementing many-to-many relationships using standard Peewee APIs, check
out the manytomany section. For all but the most simple cases, you will be better off
implementing many-to-many using the standard APIs.
through_model
The Model representing the many-to-many junction table. Will be auto-generated if not
explicitly declared.
add(value[, clear_existing=True])
Parameters
• value -- Either a Model instance, a list of model instances, or a SelectQuery.
• clear_existing (bool) -- Whether to remove existing relationships.
Associate value with the current instance. You can pass in a single model instance, a list
of model instances, or even a ModelSelect.
Example code:
# Huey needs to enroll in a bunch of courses, including all
# the English classes, and a couple Comp-Sci classes.
huey = Student.get(Student.name == 'Huey')
# We can add all the objects represented by a query.
english_courses = Course.select().where(
Course.name.contains('english'))
huey.courses.add(english_courses)
# We can also add lists of individual objects.
cs101 = Course.get(Course.name == 'CS 101')
cs151 = Course.get(Course.name == 'CS 151')
huey.courses.add([cs101, cs151])
remove(value)
Parameters
value -- Either a Model instance, a list of model instances, or a ModelSelect.
Disassociate value from the current instance. Like add(), you can pass in a model instance,
a list of model instances, or even a ModelSelect.
Example code:
# Huey is currently enrolled in a lot of english classes
# as well as some Comp-Sci. He is changing majors, so we
# will remove all his courses.
english_courses = Course.select().where(
Course.name.contains('english'))
huey.courses.remove(english_courses)
# Remove the two Comp-Sci classes Huey is enrolled in.
cs101 = Course.get(Course.name == 'CS 101')
cs151 = Course.get(Course.name == 'CS 151')
huey.courses.remove([cs101, cs151])
clear()
Remove all associated objects.
Example code:
# English 101 is canceled this semester, so remove all
# the enrollments.
english_101 = Course.get(Course.name == 'English 101')
english_101.students.clear()
get_through_model()
Return the Model representing the many-to-many junction table. This can be specified
manually when the field is being instantiated using the through_model parameter. If a
through_model is not specified, one will automatically be created.
When creating tables for an application that uses ManyToManyField, you must create the
through table expicitly.
# Get a reference to the automatically-created through table.
StudentCourseThrough = Course.students.get_through_model()
# Create tables for our two models as well as the through model.
db.create_tables([
Student,
Course,
StudentCourseThrough])
class DeferredThroughModel
Place-holder for a through-model in cases where, due to a dependency, you cannot declare either a
model or a many-to-many field without introducing NameErrors.
Example:
class Note(BaseModel):
content = TextField()
NoteThroughDeferred = DeferredThroughModel()
class User(BaseModel):
username = TextField()
notes = ManyToManyField(Note, through_model=NoteThroughDeferred)
# Cannot declare this before "User" since it has a foreign-key to
# the User model.
class NoteThrough(BaseModel):
note = ForeignKeyField(Note)
user = ForeignKeyField(User)
# Resolve dependencies.
NoteThroughDeferred.set_model(NoteThrough)
class CompositeKey(*field_names)
Parameters
field_names -- Names of fields that comprise the primary key.
A primary key composed of multiple columns. Unlike the other fields, a composite key is defined in
the model's Meta class after the fields have been defined. It takes as parameters the string names
of the fields to use as the primary key:
class BlogTagThrough(Model):
blog = ForeignKeyField(Blog, backref='tags')
tag = ForeignKeyField(Tag, backref='blogs')
class Meta:
primary_key = CompositeKey('blog', 'tag')
Schema Manager
class SchemaManager(model[, database=None[, **context_options]])
Parameters
• model (Model) -- Model class.
• database (Database) -- If unspecified defaults to model._meta.database.
Provides methods for managing the creation and deletion of tables and indexes for the given model.
create_table([safe=True[, **options]])
Parameters
• safe (bool) -- Specify IF NOT EXISTS clause.
• options -- Arbitrary options.
Execute CREATE TABLE query for the given model.
drop_table([safe=True[, drop_sequences=True[, **options]]])
Parameters
• safe (bool) -- Specify IF EXISTS clause.
• drop_sequences (bool) -- Drop any sequences associated with the columns on the
table (postgres only).
• options -- Arbitrary options.
Execute DROP TABLE query for the given model.
create_indexes([safe=True])
Parameters
safe (bool) -- Specify IF NOT EXISTS clause.
Execute CREATE INDEX queries for the indexes defined for the model.
drop_indexes([safe=True])
Parameters
safe (bool) -- Specify IF EXISTS clause.
Execute DROP INDEX queries for the indexes defined for the model.
create_sequence(field)
Parameters
field (Field) -- Field instance which specifies a sequence.
Create sequence for the given Field.
drop_sequence(field)
Parameters
field (Field) -- Field instance which specifies a sequence.
Drop sequence for the given Field.
create_foreign_key(field)
Parameters
field (ForeignKeyField) -- Foreign-key field constraint to add.
Add a foreign-key constraint for the given field. This method should not be necessary in
most cases, as foreign-key constraints are created as part of table creation. The exception
is when you are creating a circular foreign-key relationship using DeferredForeignKey. In
those cases, it is necessary to first create the tables, then add the constraint for the
deferred foreign-key:
class Language(Model):
name = TextField()
selected_snippet = DeferredForeignKey('Snippet')
class Snippet(Model):
code = TextField()
language = ForeignKeyField(Language, backref='snippets')
# Creates both tables but does not create the constraint for the
# Language.selected_snippet foreign key (because of the circular
# dependency).
db.create_tables([Language, Snippet])
# Explicitly create the constraint:
Language._schema.create_foreign_key(Language.selected_snippet)
For more information, see documentation on circular-fks.
WARNING:
Because SQLite has limited support for altering existing tables, it is not possible to
add a foreign-key constraint to an existing SQLite table.
create_all([safe=True[, **table_options]])
Parameters
safe (bool) -- Whether to specify IF NOT EXISTS.
Create sequence(s), index(es) and table for the model.
drop_all([safe=True[, drop_sequences=True[, **options]]])
Parameters
• safe (bool) -- Whether to specify IF EXISTS.
• drop_sequences (bool) -- Drop any sequences associated with the columns on the
table (postgres only).
• options -- Arbitrary options.
Drop table for the model and associated indexes.
Model
class Metadata(model[, database=None[, table_name=None[, indexes=None[, primary_key=None[,
constraints=None[, schema=None[, only_save_dirty=False[, table_alias=None[, depends_on=None[,
options=None[, without_rowid=False[, **kwargs]]]]]]]]]]]])
Parameters
• model (Model) -- Model class.
• database (Database) -- database model is bound to.
• table_name (str) -- Specify table name for model.
• indexes (list) -- List of ModelIndex objects.
• primary_key -- Primary key for model (only specified if this is a CompositeKey or False
for no primary key.
• constraints (list) -- List of table constraints.
• schema (str) -- Schema table exists in.
• only_save_dirty (bool) -- When save() is called, only save the fields which have been
modified.
• table_alias (str) -- Specify preferred alias for table in queries.
• options (dict) -- Arbitrary options for the model.
• without_rowid (bool) -- Specify WITHOUT ROWID (sqlite only).
• kwargs -- Arbitrary setting attributes and values.
Store metadata for a Model.
This class should not be instantiated directly, but is instantiated using the attributes of a
Model class' inner Meta class. Metadata attributes are then available on Model._meta.
table Return a reference to the underlying Table object.
model_graph([refs=True[, backrefs=True[, depth_first=True]]])
Parameters
• refs (bool) -- Follow foreign-key references.
• backrefs (bool) -- Follow foreign-key back-references.
• depth_first (bool) -- Do a depth-first search (False for breadth-first).
Traverse the model graph and return a list of 3-tuples, consisting of (foreign key field,
model class, is_backref).
class SubclassAwareMetadata
Metadata subclass that tracks Model subclasses.
map_models(fn)
Apply a function to all subclasses.
class Model(**kwargs)
Parameters
kwargs -- Mapping of field-name to value to initialize model with.
Model class provides a high-level abstraction for working with database tables. Models are a
one-to-one mapping with a database table (or a table-like object, such as a view). Subclasses of
Model declare any number of Field instances as class attributes. These fields correspond to
columns on the table.
Table-level operations, such as select(), update(), insert() and delete() are implemented as
classmethods. Row-level operations, such as save() and delete_instance() are implemented as
instancemethods.
Example:
db = SqliteDatabase(':memory:')
class User(Model):
username = TextField()
join_date = DateTimeField(default=datetime.datetime.now)
is_admin = BooleanField(default=False)
admin = User(username='admin', is_admin=True)
admin.save()
classmethod alias([alias=None])
Parameters
alias (str) -- Optional name for alias.
Returns
ModelAlias instance.
Create an alias to the model-class. Model aliases allow you to reference the same Model
multiple times in a query, for example when doing a self-join or sub-query.
Example:
Parent = Category.alias()
sq = (Category
.select(Category, Parent)
.join(Parent, on=(Category.parent == Parent.id))
.where(Parent.name == 'parent category'))
classmethod select(*fields)
Parameters
fields -- A list of model classes, field instances, functions or expressions. If no
arguments are provided, all columns for the given model will be selected by default.
Returns
ModelSelect query.
Create a SELECT query. If no fields are explicitly provided, the query will by default
SELECT all the fields defined on the model, unless you are using the query as a sub-query,
in which case only the primary key will be selected by default.
Example of selecting all columns:
query = User.select().where(User.active == True).order_by(User.username)
Example of selecting all columns on Tweet and the parent model, User. When the user foreign
key is accessed on a Tweet instance no additional query will be needed (see N+1 for more
details):
query = (Tweet
.select(Tweet, User)
.join(User)
.order_by(Tweet.created_date.desc()))
for tweet in query:
print(tweet.user.username, '->', tweet.content)
Example of subquery only selecting the primary key:
inactive_users = User.select().where(User.active == False)
# Here, instead of defaulting to all columns, Peewee will default
# to only selecting the primary key.
Tweet.delete().where(Tweet.user.in_(inactive_users)).execute()
classmethod update([__data=None[, **update]])
Parameters
• __data (dict) -- dict of fields to values.
• update -- Field-name to value mapping.
Create an UPDATE query.
Example showing users being marked inactive if their registration has expired:
q = (User
.update({User.active: False})
.where(User.registration_expired == True))
q.execute() # Execute the query, returning number of rows updated.
Example showing an atomic update:
q = (PageView
.update({PageView.count: PageView.count + 1})
.where(PageView.url == url))
q.execute() # Execute the query.
NOTE:
When an update query is executed, the number of rows modified will be returned.
classmethod insert([__data=None[, **insert]])
Parameters
• __data (dict) -- dict of fields to values to insert.
• insert -- Field-name to value mapping.
Create an INSERT query.
Insert a new row into the database. If any fields on the model have default values, these
values will be used if the fields are not explicitly set in the insert dictionary.
Example showing creation of a new user:
q = User.insert(username='admin', active=True, registration_expired=False)
q.execute() # perform the insert.
You can also use Field objects as the keys:
new_id = User.insert({User.username: 'admin'}).execute()
If you have a model with a default value on one of the fields, and that field is not
specified in the insert parameter, the default will be used:
class User(Model):
username = CharField()
active = BooleanField(default=True)
# This INSERT query will automatically specify `active=True`:
User.insert(username='charlie')
NOTE:
When an insert query is executed on a table with an auto-incrementing primary key, the
primary key of the new row will be returned.
classmethod insert_many(rows[, fields=None])
Parameters
• rows -- An iterable that yields rows to insert.
• fields (list) -- List of fields being inserted.
INSERT multiple rows of data.
The rows parameter must be an iterable that yields dictionaries or tuples, where the
ordering of the tuple values corresponds to the fields specified in the fields argument. As
with insert(), fields that are not specified in the dictionary will use their default
value, if one exists.
NOTE:
Due to the nature of bulk inserts, each row must contain the same fields. The following
will not work:
Person.insert_many([
{'first_name': 'Peewee', 'last_name': 'Herman'},
{'first_name': 'Huey'}, # Missing "last_name"!
]).execute()
Example of inserting multiple Users:
data = [
('charlie', True),
('huey', False),
('zaizee', False)]
query = User.insert_many(data, fields=[User.username, User.is_admin])
query.execute()
Equivalent example using dictionaries:
data = [
{'username': 'charlie', 'is_admin': True},
{'username': 'huey', 'is_admin': False},
{'username': 'zaizee', 'is_admin': False}]
# Insert new rows.
User.insert_many(data).execute()
Because the rows parameter can be an arbitrary iterable, you can also use a generator:
def get_usernames():
for username in ['charlie', 'huey', 'peewee']:
yield {'username': username}
User.insert_many(get_usernames()).execute()
WARNING:
If you are using SQLite, your SQLite library must be version 3.7.11 or newer to take
advantage of bulk inserts.
NOTE:
SQLite has a default limit of 999 bound variables per statement. This limit can be
modified at compile-time or at run-time, but if modifying at run-time, you can only
specify a lower value than the default limit.
For more information, check out the following SQLite documents:
• Max variable number limit
• Changing run-time limits
• SQLite compile-time flags
classmethod insert_from(query, fields)
Parameters
• query (Select) -- SELECT query to use as source of data.
• fields -- Fields to insert data into.
INSERT data using a SELECT query as the source. This API should be used for queries of the
form INSERT INTO ... SELECT FROM ....
Example of inserting data across tables for denormalization purposes:
source = (User
.select(User.username, fn.COUNT(Tweet.id))
.join(Tweet, JOIN.LEFT_OUTER)
.group_by(User.username))
UserTweetDenorm.insert_from(
source,
[UserTweetDenorm.username, UserTweetDenorm.num_tweets]).execute()
classmethod replace([__data=None[, **insert]])
Parameters
• __data (dict) -- dict of fields to values to insert.
• insert -- Field-name to value mapping.
Create an INSERT query that uses REPLACE for conflict-resolution.
See Model.insert() for examples.
classmethod replace_many(rows[, fields=None])
Parameters
• rows -- An iterable that yields rows to insert.
• fields (list) -- List of fields being inserted.
INSERT multiple rows of data using REPLACE for conflict-resolution.
See Model.insert_many() for examples.
classmethod raw(sql, *params)
Parameters
• sql (str) -- SQL query to execute.
• params -- Parameters for query.
Execute a SQL query directly.
Example selecting rows from the User table:
q = User.raw('select id, username from users')
for user in q:
print(user.id, user.username)
NOTE:
Generally the use of raw is reserved for those cases where you can significantly
optimize a select query. It is useful for select queries since it will return instances
of the model.
classmethod delete()
Create a DELETE query.
Example showing the deletion of all inactive users:
q = User.delete().where(User.active == False)
q.execute() # Remove the rows, return number of rows removed.
WARNING:
This method performs a delete on the entire table. To delete a single instance, see
Model.delete_instance().
classmethod create(**query)
Parameters
query -- Mapping of field-name to value.
INSERT new row into table and return corresponding model instance.
Example showing the creation of a user (a row will be added to the database):
user = User.create(username='admin', password='test')
NOTE:
The create() method is a shorthand for instantiate-then-save.
classmethod bulk_create(model_list[, batch_size=None])
Parameters
• model_list (iterable) -- a list or other iterable of unsaved Model instances.
• batch_size (int) -- number of rows to batch per insert. If unspecified, all models
will be inserted in a single query.
Returns
no return value.
Efficiently INSERT multiple unsaved model instances into the database. Unlike
insert_many(), which accepts row data as a list of either dictionaries or lists, this
method accepts a list of unsaved model instances.
Example:
# List of 10 unsaved users.
user_list = [User(username='u%s' % i) for i in range(10)]
# All 10 users are inserted in a single query.
User.bulk_create(user_list)
Batches:
user_list = [User(username='u%s' % i) for i in range(10)]
with database.atomic():
# Will execute 4 INSERT queries (3 batches of 3, 1 batch of 1).
User.bulk_create(user_list, batch_size=3)
WARNING:
• The primary-key value for the newly-created models will only be set if you are using
Postgresql (which supports the RETURNING clause).
• SQLite generally has a limit of 999 bound parameters for a query, so the batch size
should be roughly 1000 / number-of-fields.
• When a batch-size is provided it is strongly recommended that you wrap the call in a
transaction or savepoint using Database.atomic(). Otherwise an error in a batch
mid-way through could leave the database in an inconsistent state.
classmethod get(*query, **filters)
Parameters
• query -- Zero or more Expression objects.
• filters -- Mapping of field-name to value for Django-style filter.
Raises DoesNotExist
Returns
Model instance matching the specified filters.
Retrieve a single model instance matching the given filters. If no model is returned, a
DoesNotExist is raised.
user = User.get(User.username == username, User.active == True)
This method is also exposed via the SelectQuery, though it takes no parameters:
active = User.select().where(User.active == True)
try:
user = active.where(
(User.username == username) &
(User.active == True)
).get()
except User.DoesNotExist:
user = None
NOTE:
The get() method is shorthand for selecting with a limit of 1. It has the added behavior
of raising an exception when no matching row is found. If more than one row is found,
the first row returned by the database cursor will be used.
classmethod get_or_none(*query, **filters)
Identical to Model.get() but returns None if no model matches the given filters.
classmethod get_by_id(pk)
Parameters
pk -- Primary-key value.
Short-hand for calling Model.get() specifying a lookup by primary key. Raises a
DoesNotExist if instance with the given primary key value does not exist.
Example:
user = User.get_by_id(1) # Returns user with id = 1.
classmethod set_by_id(key, value)
Parameters
• key -- Primary-key value.
• value (dict) -- Mapping of field to value to update.
Short-hand for updating the data with the given primary-key. If no row exists with the
given primary key, no exception will be raised.
Example:
# Set "is_admin" to True on user with id=3.
User.set_by_id(3, {'is_admin': True})
classmethod delete_by_id(pk)
Parameters
pk -- Primary-key value.
Short-hand for deleting the row with the given primary-key. If no row exists with the given
primary key, no exception will be raised.
classmethod get_or_create(**kwargs)
Parameters
• kwargs -- Mapping of field-name to value.
• defaults -- Default values to use if creating a new row.
Returns
Tuple of Model instance and boolean indicating if a new object was created.
Attempt to get the row matching the given filters. If no matching row is found, create a
new row.
WARNING:
Race-conditions are possible when using this method.
Example without get_or_create:
# Without `get_or_create`, we might write:
try:
person = Person.get(
(Person.first_name == 'John') &
(Person.last_name == 'Lennon'))
except Person.DoesNotExist:
person = Person.create(
first_name='John',
last_name='Lennon',
birthday=datetime.date(1940, 10, 9))
Equivalent code using get_or_create:
person, created = Person.get_or_create(
first_name='John',
last_name='Lennon',
defaults={'birthday': datetime.date(1940, 10, 9)})
classmethod filter(*dq_nodes, **filters)
Parameters
• dq_nodes -- Zero or more DQ objects.
• filters -- Django-style filters.
Returns
ModelSelect query.
get_id()
Returns
The primary-key of the model instance.
save([force_insert=False[, only=None]])
Parameters
• force_insert (bool) -- Force INSERT query.
• only (list) -- Only save the given Field instances.
Returns
Number of rows modified.
Save the data in the model instance. By default, the presence of a primary-key value will
cause an UPDATE query to be executed.
Example showing saving a model instance:
user = User()
user.username = 'some-user' # does not touch the database
user.save() # change is persisted to the db
dirty_fields
Return list of fields that have been modified.
Return type
list
NOTE:
If you just want to persist modified fields, you can call
model.save(only=model.dirty_fields).
If you always want to only save a model's dirty fields, you can use the Meta option
only_save_dirty = True. Then, any time you call Model.save(), by default only the dirty
fields will be saved, e.g.
class Person(Model):
first_name = CharField()
last_name = CharField()
dob = DateField()
class Meta:
database = db
only_save_dirty = True
WARNING:
Peewee determines whether a field is "dirty" by observing when the field attribute is
set on a model instance. If the field contains a value that is mutable, such as a
dictionary instance, and that dictionary is then modified, Peewee will not notice the
change.
is_dirty()
Return boolean indicating whether any fields were manually set.
delete_instance([recursive=False[, delete_nullable=False]])
Parameters
• recursive (bool) -- Delete related models.
• delete_nullable (bool) -- Delete related models that have a null foreign key. If
False nullable relations will be set to NULL.
Delete the given instance. Any foreign keys set to cascade on delete will be deleted
automatically. For more programmatic control, you can specify recursive=True, which will
delete any non-nullable related models (those that are nullable will be set to NULL). If
you wish to delete all dependencies regardless of whether they are nullable, set
delete_nullable=True.
example:
some_obj.delete_instance() # it is gone forever
classmethod bind(database[, bind_refs=True[, bind_backrefs=True]])
Parameters
• database (Database) -- database to bind to.
• bind_refs (bool) -- Bind related models.
• bind_backrefs (bool) -- Bind back-reference related models.
Bind the model (and specified relations) to the given database.
See also: Database.bind().
classmethod bind_ctx(database[, bind_refs=True[, bind_backrefs=True]])
Like bind(), but returns a context manager that only binds the models for the duration of
the wrapped block.
See also: Database.bind_ctx().
classmethod table_exists()
Returns
boolean indicating whether the table exists.
classmethod create_table([safe=True[, **options]])
Parameters
safe (bool) -- If set to True, the create table query will include an IF NOT EXISTS
clause.
Create the model table, indexes, constraints and sequences.
Example:
with database:
SomeModel.create_table() # Execute the create table query.
classmethod drop_table([safe=True[, **options]])
Parameters
safe (bool) -- If set to True, the create table query will include an IF EXISTS
clause.
Drop the model table.
classmethod index(*fields[, unique=False[, safe=True[, where=None[, using=None[, name=None]]]]])
Parameters
• fields -- Fields to index.
• unique (bool) -- Whether index is UNIQUE.
• safe (bool) -- Whether to add IF NOT EXISTS clause.
• where (Expression) -- Optional WHERE clause for index.
• using (str) -- Index algorithm.
• name (str) -- Optional index name.
Expressive method for declaring an index on a model. Wraps the declaration of a ModelIndex
instance.
Examples:
class Article(Model):
name = TextField()
timestamp = TimestampField()
status = IntegerField()
flags = BitField()
is_sticky = flags.flag(1)
is_favorite = flags.flag(2)
# CREATE INDEX ... ON "article" ("name", "timestamp" DESC)
idx = Article.index(Article.name, Article.timestamp.desc())
# Be sure to add the index to the model:
Article.add_index(idx)
# CREATE UNIQUE INDEX ... ON "article" ("timestamp" DESC, "flags" & 2)
# WHERE ("status" = 1)
idx = (Article
.index(Article.timestamp.desc(),
Article.flags.bin_and(2),
unique=True)
.where(Article.status == 1))
# Add index to model:
Article.add_index(idx)
classmethod add_index(*args, **kwargs)
Parameters
• args -- a ModelIndex instance, Field(s) to index, or a SQL instance that contains
the SQL for creating the index.
• kwargs -- Keyword arguments passed to ModelIndex constructor.
Add an index to the model's definition.
NOTE:
This method does not actually create the index in the database. Rather, it adds the
index definition to the model's metadata, so that a subsequent call to create_table()
will create the new index (along with the table).
Examples:
class Article(Model):
name = TextField()
timestamp = TimestampField()
status = IntegerField()
flags = BitField()
is_sticky = flags.flag(1)
is_favorite = flags.flag(2)
# CREATE INDEX ... ON "article" ("name", "timestamp") WHERE "status" = 1
idx = Article.index(Article.name, Article.timestamp).where(Article.status == 1)
Article.add_index(idx)
# CREATE UNIQUE INDEX ... ON "article" ("timestamp" DESC, "flags" & 2)
ts_flags_idx = Article.index(
Article.timestamp.desc(),
Article.flags.bin_and(2),
unique=True)
Article.add_index(ts_flags_idx)
# You can also specify a list of fields and use the same keyword
# arguments that the ModelIndex constructor accepts:
Article.add_index(
Article.name,
Article.timestamp.desc(),
where=(Article.status == 1))
# Or even specify a SQL query directly:
Article.add_index(SQL('CREATE INDEX ...'))
dependencies([search_nullable=False])
Parameters
search_nullable (bool) -- Search models related via a nullable foreign key
Return type
Generator expression yielding queries and foreign key fields.
Generate a list of queries of dependent models. Yields a 2-tuple containing the query and
corresponding foreign key field. Useful for searching dependencies of a model, i.e. things
that would be orphaned in the event of a delete.
__iter__()
Returns
a ModelSelect for the given class.
Convenience function for iterating over all instances of a model.
Example:
Setting.insert_many([
{'key': 'host', 'value': '192.168.1.2'},
{'key': 'port': 'value': '1337'},
{'key': 'user': 'value': 'nuggie'}]).execute()
# Load settings from db into dict.
settings = {setting.key: setting.value for setting in Setting}
__len__()
Returns
Count of rows in table.
Example:
n_accounts = len(Account)
# Is equivalent to:
n_accounts = Account.select().count()
class ModelAlias(model[, alias=None])
Parameters
• model (Model) -- Model class to reference.
• alias (str) -- (optional) name for alias.
Provide a separate reference to a model in a query.
class ModelSelect(model, fields_or_models)
Parameters
• model (Model) -- Model class to select.
• fields_or_models -- List of fields or model classes to select.
Model-specific implementation of SELECT query.
switch([ctx=None])
Parameters
ctx -- A Model, ModelAlias, subquery, or other object that was joined-on.
Switch the join context - the source which subsequent calls to join() will be joined
against. Used for specifying multiple joins against a single table.
If the ctx is not given, then the query's model will be used.
The following example selects from tweet and joins on both user and tweet-flag:
sq = Tweet.select().join(User).switch(Tweet).join(TweetFlag)
# Equivalent (since Tweet is the query's model)
sq = Tweet.select().join(User).switch().join(TweetFlag)
objects([constructor=None])
Parameters
constructor -- Constructor (defaults to returning model instances)
Return result rows as objects created using the given constructor. The default behavior is
to create model instances.
NOTE:
This method can be used, when selecting field data from multiple sources/models, to make
all data available as attributes on the model being queried (as opposed to constructing
the graph of joined model instances). For very complex queries this can have a positive
performance impact, especially iterating large result sets.
Similarly, you can use dicts(), tuples() or namedtuples() to achieve even more
performance.
join(dest[, join_type='INNER'[, on=None[, src=None[, attr=None]]]])
Parameters
• dest -- A Model, ModelAlias, Select query, or other object to join to.
• join_type (str) -- Join type, defaults to INNER.
• on -- Join predicate or a ForeignKeyField to join on.
• src -- Explicitly specify the source of the join. If not specified then the
current join context will be used.
• attr (str) -- Attribute to use when projecting columns from the joined model.
Join with another table-like object.
Join type may be one of:
• JOIN.INNER
• JOIN.LEFT_OUTER
• JOIN.RIGHT_OUTER
• JOIN.FULL
• JOIN.FULL_OUTER
• JOIN.CROSS
Example selecting tweets and joining on user in order to restrict to only those tweets made
by "admin" users:
sq = Tweet.select().join(User).where(User.is_admin == True)
Example selecting users and joining on a particular foreign key field. See the example app
for a real-life usage:
sq = User.select().join(Relationship, on=Relationship.to_user)
For an in-depth discussion of foreign-keys, joins and relationships between models, refer
to relationships.
join_from(src, dest[, join_type='INNER'[, on=None[, attr=None]]])
Parameters
• src -- Source for join.
• dest -- Table to join to.
Use same parameter order as the non-model-specific join(). Bypasses the join context by
requiring the join source to be specified.
filter(*args, **kwargs)
Parameters
• args -- Zero or more DQ objects.
• kwargs -- Django-style keyword-argument filters.
Use Django-style filters to express a WHERE clause.
prefetch(*subqueries)
Parameters
subqueries -- A list of Model classes or select queries to prefetch.
Execute the query, prefetching the given additional resources.
See also prefetch() standalone function.
Example:
# Fetch all Users and prefetch their associated tweets.
query = User.select().prefetch(Tweet)
for user in query:
print(user.username)
for tweet in user.tweets:
print(' *', tweet.content)
prefetch(sq, *subqueries)
Parameters
• sq -- Query to use as starting-point.
• subqueries -- One or more models or ModelSelect queries to eagerly fetch.
Eagerly fetch related objects, allowing efficient querying of multiple tables when a 1-to-many
relationship exists.
For example, it is simple to query a many-to-1 relationship efficiently:
query = (Tweet
.select(Tweet, User)
.join(User))
for tweet in query:
# Looking up tweet.user.username does not require a query since
# the related user's columns were selected.
print(tweet.user.username, '->', tweet.content)
To efficiently do the inverse, query users and their tweets, you can use prefetch:
query = User.select()
for user in prefetch(query, Tweet):
print(user.username)
for tweet in user.tweets: # Does not require additional query.
print(' ', tweet.content)
Query-builder Internals
class AliasManager
Manages the aliases assigned to Source objects in SELECT queries, so as to avoid ambiguous
references when multiple sources are used in a single query.
add(source)
Add a source to the AliasManager's internal registry at the current scope. The alias will
be automatically generated using the following scheme (where each level of indentation
refers to a new scope):
Parameters
source (Source) -- Make the manager aware of a new source. If the source has already
been added, the call is a no-op.
get(source[, any_depth=False])
Return the alias for the source in the current scope. If the source does not have an alias,
it will be given the next available alias.
Parameters
source (Source) -- The source whose alias should be retrieved.
Returns
The alias already assigned to the source, or the next available alias.
Return type
str
__setitem__(source, alias)
Manually set the alias for the source at the current scope.
Parameters
source (Source) -- The source for which we set the alias.
push() Push a new scope onto the stack.
pop() Pop scope from the stack.
class State(scope[, parentheses=False[, subquery=False[, **kwargs]]])
Lightweight object for representing the state at a given scope. During SQL generation, each object
visited by the Context can inspect the state. The State class allows Peewee to do things like:
• Use a common interface for field types or SQL expressions, but use vendor-specific data-types or
operators.
• Compile a Column instance into a fully-qualified attribute, as a named alias, etc, depending on
the value of the scope.
• Ensure parentheses are used appropriately.
Parameters
• scope (int) -- The scope rules to be applied while the state is active.
• parentheses (bool) -- Wrap the contained SQL in parentheses.
• subquery (bool) -- Whether the current state is a child of an outer query.
• kwargs (dict) -- Arbitrary settings which should be applied in the current state.
class Context(**settings)
Converts Peewee structures into parameterized SQL queries.
Peewee structures should all implement a __sql__ method, which will be called by the Context class
during SQL generation. The __sql__ method accepts a single parameter, the Context instance, which
allows for recursive descent and introspection of scope and state.
scope Return the currently-active scope rules.
parentheses
Return whether the current state is wrapped in parentheses.
subquery
Return whether the current state is the child of another query.
scope_normal([**kwargs])
The default scope. Sources are referred to by alias, columns by dotted-path from the
source.
scope_source([**kwargs])
Scope used when defining sources, e.g. in the column list and FROM clause of a SELECT
query. This scope is used for defining the fully-qualified name of the source and assigning
an alias.
scope_values([**kwargs])
Scope used for UPDATE, INSERT or DELETE queries, where instead of referencing a source by
an alias, we refer to it directly. Similarly, since there is a single table, columns do not
need to be referenced by dotted-path.
scope_cte([**kwargs])
Scope used when generating the contents of a common-table-expression. Used after a WITH
statement, when generating the definition for a CTE (as opposed to merely a reference to
one).
scope_column([**kwargs])
Scope used when generating SQL for a column. Ensures that the column is rendered with it's
correct alias. Was needed because when referencing the inner projection of a sub-select,
Peewee would render the full SELECT query as the "source" of the column (instead of the
query's alias + . + column). This scope allows us to avoid rendering the full query when
we only need the alias.
sql(obj)
Append a composable Node object, sub-context, or other object to the query AST. Python
values, such as integers, strings, floats, etc. are treated as parameterized values.
Returns
The updated Context object.
literal(keyword)
Append a string-literal to the current query AST.
Returns
The updated Context object.
parse(node)
Parameters
node (Node) -- Instance of a Node subclass.
Returns
a 2-tuple consisting of (sql, parameters).
Convert the given node to a SQL AST and return a 2-tuple consisting of the SQL query and
the parameters.
query()
Returns
a 2-tuple consisting of (sql, parameters) for the context.
Constants and Helpers
class Proxy
Create a proxy or placeholder for another object.
initialize(obj)
Parameters
obj -- Object to proxy to.
Bind the proxy to the given object. Afterwards all attribute lookups and method calls on
the proxy will be sent to the given object.
Any callbacks that have been registered will be called.
attach_callback(callback)
Parameters
callback -- A function that accepts a single parameter, the bound object.
Returns
self
Add a callback to be executed when the proxy is initialized.
chunked(iterable, n)
Parameters
• iterable -- an iterable that is the source of the data to be chunked.
• n (int) -- chunk size
Returns
a new iterable that yields n-length chunks of the source data.
Efficient implementation for breaking up large lists of data into smaller-sized chunks.
Usage:
it = range(10) # An iterable that yields 0...9.
# Break the iterable into chunks of length 4.
for chunk in chunked(it, 4):
print(', '.join(str(num) for num in chunk))
# PRINTS:
# 0, 1, 2, 3
# 4, 5, 6, 7
# 8, 9
SQLite Extensions
The default SqliteDatabase already includes many SQLite-specific features:
• General notes on using SQLite.
• Configuring SQLite using PRAGMA statements.
• User-defined functions, aggregate and collations.
• Locking modes for transactions.
The playhouse.sqlite_ext includes even more SQLite features, including:
• Full-text search
• JSON extension integration
• Closure table extension support
• LSM1 extension support
• User-defined table functions
• Support for online backups using backup API: backup_to_file()
• BLOB API support, for efficient binary data storage.
• Additional helpers, including bloom filter, more.
Getting started
To get started with the features described in this document, you will want to use the SqliteExtDatabase
class from the playhouse.sqlite_ext module. Furthermore, some features require the playhouse._sqlite_ext
C extension -- these features will be noted in the documentation.
Instantiating a SqliteExtDatabase:
from playhouse.sqlite_ext import SqliteExtDatabase
db = SqliteExtDatabase('my_app.db', pragmas=(
('cache_size', -1024 * 64), # 64MB page-cache.
('journal_mode', 'wal'), # Use WAL-mode (you should always use this!).
('foreign_keys', 1)) # Enforce foreign-key constraints.
APIs
class SqliteExtDatabase(database[, pragmas=None[, timeout=5[, c_extensions=None[, rank_functions=True[,
hash_functions=False[, regexp_function=False[, bloomfilter=False]]]]]]])
Parameters
• pragmas (list) -- A list of 2-tuples containing pragma key and value to set every time a
connection is opened.
• timeout -- Set the busy-timeout on the SQLite driver (in seconds).
• c_extensions (bool) -- Declare that C extension speedups must/must-not be used. If set to
True and the extension module is not available, will raise an ImproperlyConfigured
exception.
• rank_functions (bool) -- Make search result ranking functions available.
• hash_functions (bool) -- Make hashing functions available (md5, sha1, etc).
• regexp_function (bool) -- Make the REGEXP function available.
• bloomfilter (bool) -- Make the bloom filter available.
Extends SqliteDatabase and inherits methods for declaring user-defined functions, pragmas, etc.
class CSqliteExtDatabase(database[, pragmas=None[, timeout=5[, c_extensions=None[, rank_functions=True[,
hash_functions=False[, regexp_function=False[, bloomfilter=False[, replace_busy_handler=False]]]]]]]])
Parameters
• pragmas (list) -- A list of 2-tuples containing pragma key and value to set every time a
connection is opened.
• timeout -- Set the busy-timeout on the SQLite driver (in seconds).
• c_extensions (bool) -- Declare that C extension speedups must/must-not be used. If set to
True and the extension module is not available, will raise an ImproperlyConfigured
exception.
• rank_functions (bool) -- Make search result ranking functions available.
• hash_functions (bool) -- Make hashing functions available (md5, sha1, etc).
• regexp_function (bool) -- Make the REGEXP function available.
• bloomfilter (bool) -- Make the bloom filter available.
• replace_busy_handler (bool) -- Use a smarter busy-handler implementation.
Extends SqliteExtDatabase and requires that the playhouse._sqlite_ext extension module be
available.
on_commit(fn)
Register a callback to be executed whenever a transaction is committed on the current
connection. The callback accepts no parameters and the return value is ignored.
However, if the callback raises a ValueError, the transaction will be aborted and
rolled-back.
Example:
db = CSqliteExtDatabase(':memory:')
@db.on_commit
def on_commit():
logger.info('COMMITing changes')
on_rollback(fn)
Register a callback to be executed whenever a transaction is rolled back on the current
connection. The callback accepts no parameters and the return value is ignored.
Example:
@db.on_rollback
def on_rollback():
logger.info('Rolling back changes')
on_update(fn)
Register a callback to be executed whenever the database is written to (via an UPDATE,
INSERT or DELETE query). The callback should accept the following parameters:
• query - the type of query, either INSERT, UPDATE or DELETE.
• database name - the default database is named main.
• table name - name of table being modified.
• rowid - the rowid of the row being modified.
The callback's return value is ignored.
Example:
db = CSqliteExtDatabase(':memory:')
@db.on_update
def on_update(query_type, db, table, rowid):
# e.g. INSERT row 3 into table users.
logger.info('%s row %s into table %s', query_type, rowid, table)
changes()
Return the number of rows modified in the currently-open transaction.
autocommit
Property which returns a boolean indicating if autocommit is enabled. By default, this
value will be True except when inside a transaction (or atomic() block).
Example:
>>> db = CSqliteExtDatabase(':memory:')
>>> db.autocommit
True
>>> with db.atomic():
... print(db.autocommit)
...
False
>>> db.autocommit
True
backup(destination[, pages=None, name=None, progress=None])
Parameters
• destination (SqliteDatabase) -- Database object to serve as destination for the
backup.
• pages (int) -- Number of pages per iteration. Default value of -1 indicates all
pages should be backed-up in a single step.
• name (str) -- Name of source database (may differ if you used ATTACH DATABASE to
load multiple databases). Defaults to "main".
• progress -- Progress callback, called with three parameters: the number of pages
remaining, the total page count, and whether the backup is complete.
Example:
master = CSqliteExtDatabase('master.db')
replica = CSqliteExtDatabase('replica.db')
# Backup the contents of master to replica.
master.backup(replica)
backup_to_file(filename[, pages, name, progress])
Parameters
• filename -- Filename to store the database backup.
• pages (int) -- Number of pages per iteration. Default value of -1 indicates all
pages should be backed-up in a single step.
• name (str) -- Name of source database (may differ if you used ATTACH DATABASE to
load multiple databases). Defaults to "main".
• progress -- Progress callback, called with three parameters: the number of pages
remaining, the total page count, and whether the backup is complete.
Backup the current database to a file. The backed-up data is not a database dump, but an
actual SQLite database file.
Example:
db = CSqliteExtDatabase('app.db')
def nightly_backup():
filename = 'backup-%s.db' % (datetime.date.today())
db.backup_to_file(filename)
blob_open(table, column, rowid[, read_only=False])
Parameters
• table (str) -- Name of table containing data.
• column (str) -- Name of column containing data.
• rowid (int) -- ID of row to retrieve.
• read_only (bool) -- Open the blob for reading only.
Returns
Blob instance which provides efficient access to the underlying binary data.
Return type
Blob
See Blob and ZeroBlob for more information.
Example:
class Image(Model):
filename = TextField()
data = BlobField()
buf_size = 1024 * 1024 * 8 # Allocate 8MB for storing file.
rowid = Image.insert({Image.filename: 'thefile.jpg',
Image.data: ZeroBlob(buf_size)}).execute()
# Open the blob, returning a file-like object.
blob = db.blob_open('image', 'data', rowid)
# Write some data to the blob.
blob.write(image_data)
img_size = blob.tell()
# Read the data back out of the blob.
blob.seek(0)
image_data = blob.read(img_size)
class RowIDField
Primary-key field that corresponds to the SQLite rowid field. For more information, see the SQLite
documentation on rowid tables..
Example:
class Note(Model):
rowid = RowIDField() # Will be primary key.
content = TextField()
timestamp = TimestampField()
class DocIDField
Subclass of RowIDField for use on virtual tables that specifically use the convention of docid for
the primary key. As far as I know this only pertains to tables using the FTS3 and FTS4 full-text
search extensions.
ATTENTION:
In FTS3 and FTS4, "docid" is simply an alias for "rowid". To reduce confusion, it's probably
best to just always use RowIDField and never use DocIDField.
class NoteIndex(FTSModel):
docid = DocIDField() # "docid" is used as an alias for "rowid".
content = SearchField()
class Meta:
database = db
class AutoIncrementField
SQLite, by default, may reuse primary key values after rows are deleted. To ensure that the
primary key is always monotonically increasing, regardless of deletions, you should use
AutoIncrementField. There is a small performance cost for this feature. For more information, see
the SQLite docs on autoincrement.
class JSONField
Field class suitable for storing JSON data, with special methods designed to work with the json1
extension.
SQLite 3.9.0 added JSON support in the form of an extension library. The SQLite json1 extension
provides a number of helper functions for working with JSON data. These APIs are exposed as
methods of a special field-type, JSONField.
To access or modify specific object keys or array indexes in a JSON structure, you can treat the
JSONField as if it were a dictionary/list.
Let's look at some examples of using the SQLite json1 extension with Peewee. Here we'll prepare a
database and a simple model for testing the json1 extension:
>>> from playhouse.sqlite_ext import *
>>> db = SqliteExtDatabase(':memory:')
>>> class KV(Model):
... key = TextField()
... value = JSONField()
... class Meta:
... database = db
...
>>> KV.create_table()
Storing data works as you might expect. There's no need to serialize dictionaries or lists as
JSON, as this is done automatically by Peewee:
>>> KV.create(key='a', value={'k1': 'v1'})
<KV: 1>
>>> KV.get(KV.key == 'a').value
{'k1': 'v1'}
We can access specific parts of the JSON data using dictionary lookups:
>>> KV.get(KV.value['k1'] == 'v1').key
'a'
It's possible to update a JSON value in-place using the update() method. Note that "k1=v1" is
preserved:
>>> KV.update(value=KV.value.update({'k2': 'v2', 'k3': 'v3'})).execute()
1
>>> KV.get(KV.key == 'a').value
{'k1': 'v1', 'k2': 'v2', 'k3': 'v3'}
We can also update existing data atomically, or remove keys by setting their value to None. In the
following example, we'll update the value of "k1" and remove "k3" ("k2" will not be modified):
>>> KV.update(value=KV.value.update({'k1': 'v1-x', 'k3': None})).execute()
1
>>> KV.get(KV.key == 'a').value
{'k1': 'v1-x', 'k2': 'v2'}
We can also set individual parts of the JSON data using the set() method:
>>> KV.update(value=KV.value['k1'].set('v1')).execute()
1
>>> KV.get(KV.key == 'a').value
{'k1': 'v1', 'k2': 'v2'}
The set() method can also be used with objects, in addition to scalar values:
>>> KV.update(value=KV.value['k2'].set({'x2': 'y2'})).execute()
1
>>> KV.get(KV.key == 'a').value
{'k1': 'v1', 'k2': {'x2': 'y2'}}
Individual parts of the JSON data can be removed atomically as well, using remove():
>>> KV.update(value=KV.value['k2'].remove()).execute()
1
>>> KV.get(KV.key == 'a').value
{'k1': 'v1'}
We can also get the type of value stored at a specific location in the JSON data using the
json_type() method:
>>> KV.select(KV.value.json_type(), KV.value['k1'].json_type()).tuples()[:]
[('object', 'text')]
Let's add a nested value and then see how to iterate through it's contents recursively using the
tree() method:
>>> KV.create(key='b', value={'x1': {'y1': 'z1', 'y2': 'z2'}, 'x2': [1, 2]})
<KV: 2>
>>> tree = KV.value.tree().alias('tree')
>>> query = KV.select(KV.key, tree.c.fullkey, tree.c.value).from_(KV, tree)
>>> query.tuples()[:]
[('a', '$', {'k1': 'v1'}),
('a', '$.k1', 'v1'),
('b', '$', {'x1': {'y1': 'z1', 'y2': 'z2'}, 'x2': [1, 2]}),
('b', '$.x2', [1, 2]),
('b', '$.x2[0]', 1),
('b', '$.x2[1]', 2),
('b', '$.x1', {'y1': 'z1', 'y2': 'z2'}),
('b', '$.x1.y1', 'z1'),
('b', '$.x1.y2', 'z2')]
The tree() and children() methods are powerful. For more information on how to utilize them, see
the json1 extension documentation.
Also note, that JSONField lookups can be chained:
>>> query = KV.select().where(KV.value['x1']['y1'] == 'z1')
>>> for obj in query:
... print(obj.key, obj.value)
...
'b', {'x1': {'y1': 'z1', 'y2': 'z2'}, 'x2': [1, 2]}
For more information, refer to the sqlite json1 documentation.
__getitem__(item)
Parameters
item -- Access a specific key or array index in the JSON data.
Returns
a special object exposing access to the JSON data.
Return type
JSONPath
Access a specific key or array index in the JSON data. Returns a JSONPath object, which
exposes convenient methods for reading or modifying a particular part of a JSON object.
Example:
# If metadata contains {"tags": ["list", "of", "tags"]}, we can
# extract the first tag in this way:
Post.select(Post, Post.metadata['tags'][0].alias('first_tag'))
For more examples see the JSONPath API documentation.
set(value[, as_json=None])
Parameters
• value -- a scalar value, list, or dictionary.
• as_json (bool) -- force the value to be treated as JSON, in which case it will be
serialized as JSON in Python beforehand. By default, lists and dictionaries are
treated as JSON to be serialized, while strings and integers are passed as-is.
Set the value stored in a JSONField.
Uses the json_set() function from the json1 extension.
update(data)
Parameters
data -- a scalar value, list or dictionary to merge with the data currently stored
in a JSONField. To remove a particular key, set that key to None in the updated
data.
Merge new data into the JSON value using the RFC-7396 MergePatch algorithm to apply a patch
(data parameter) against the column data. MergePatch can add, modify, or delete elements of
a JSON object, which means update() is a generalized replacement for both set() and
remove(). MergePatch treats JSON array objects as atomic, so update() cannot append to an
array, nor modify individual elements of an array.
For more information as well as examples, see the SQLite json_patch() function
documentation.
remove()
Remove the data stored in the JSONField.
Uses the json_type function from the json1 extension.
json_type()
Return a string identifying the type of value stored in the column.
The type returned will be one of:
• object
• array
• integer
• real
• true
• false
• text
• null <-- the string "null" means an actual NULL value
• NULL <-- an actual NULL value means the path was not found
Uses the json_type function from the json1 extension.
length()
Return the length of the array stored in the column.
Uses the json_array_length function from the json1 extension.
children()
The children function corresponds to json_each, a table-valued function that walks the JSON
value provided and returns the immediate children of the top-level array or object. If a
path is specified, then that path is treated as the top-most element.
The rows returned by calls to children() have the following attributes:
• key: the key of the current element relative to its parent.
• value: the value of the current element.
• type: one of the data-types (see json_type()).
• atom: the scalar value for primitive types, NULL for arrays and objects.
• id: a unique ID referencing the current node in the tree.
• parent: the ID of the containing node.
• fullkey: the full path describing the current element.
• path: the path to the container of the current row.
Internally this method uses the json_each (documentation link) function from the json1
extension.
Example usage (compare to tree() method):
class KeyData(Model):
key = TextField()
data = JSONField()
KeyData.create(key='a', data={'k1': 'v1', 'x1': {'y1': 'z1'}})
KeyData.create(key='b', data={'x1': {'y1': 'z1', 'y2': 'z2'}})
# We will query the KeyData model for the key and all the
# top-level keys and values in it's data field.
kd = KeyData.data.children().alias('children')
query = (KeyData
.select(kd.c.key, kd.c.value, kd.c.fullkey)
.from_(KeyData, kd)
.order_by(kd.c.key)
.tuples())
print(query[:])
# PRINTS:
[('a', 'k1', 'v1', '$.k1'),
('a', 'x1', '{"y1":"z1"}', '$.x1'),
('b', 'x1', '{"y1":"z1","y2":"z2"}', '$.x1')]
tree() The tree function corresponds to json_tree, a table-valued function that recursively walks
the JSON value provided and returns information about the keys at each level. If a path is
specified, then that path is treated as the top-most element.
The rows returned by calls to tree() have the same attributes as rows returned by calls to
children():
• key: the key of the current element relative to its parent.
• value: the value of the current element.
• type: one of the data-types (see json_type()).
• atom: the scalar value for primitive types, NULL for arrays and objects.
• id: a unique ID referencing the current node in the tree.
• parent: the ID of the containing node.
• fullkey: the full path describing the current element.
• path: the path to the container of the current row.
Internally this method uses the json_tree (documentation link) function from the json1
extension.
Example usage:
class KeyData(Model):
key = TextField()
data = JSONField()
KeyData.create(key='a', data={'k1': 'v1', 'x1': {'y1': 'z1'}})
KeyData.create(key='b', data={'x1': {'y1': 'z1', 'y2': 'z2'}})
# We will query the KeyData model for the key and all the
# keys and values in it's data field, recursively.
kd = KeyData.data.tree().alias('tree')
query = (KeyData
.select(kd.c.key, kd.c.value, kd.c.fullkey)
.from_(KeyData, kd)
.order_by(kd.c.key)
.tuples())
print(query[:])
# PRINTS:
[('a', None, '{"k1":"v1","x1":{"y1":"z1"}}', '$'),
('b', None, '{"x1":{"y1":"z1","y2":"z2"}}', '$'),
('a', 'k1', 'v1', '$.k1'),
('a', 'x1', '{"y1":"z1"}', '$.x1'),
('b', 'x1', '{"y1":"z1","y2":"z2"}', '$.x1'),
('a', 'y1', 'z1', '$.x1.y1'),
('b', 'y1', 'z1', '$.x1.y1'),
('b', 'y2', 'z2', '$.x1.y2')]
class JSONPath(field[, path=None])
Parameters
• field (JSONField) -- the field object we intend to access.
• path (tuple) -- Components comprising the JSON path.
A convenient, Pythonic way of representing JSON paths for use with JSONField.
The JSONPath object implements __getitem__, accumulating path components, which it can turn into
the corresponding json-path expression.
__getitem__(item)
Parameters
item -- Access a sub-key key or array index.
Returns
a JSONPath representing the new path.
Access a sub-key or array index in the JSON data. Returns a JSONPath object, which exposes
convenient methods for reading or modifying a particular part of a JSON object.
Example:
# If metadata contains {"tags": ["list", "of", "tags"]}, we can
# extract the first tag in this way:
first_tag = Post.metadata['tags'][0]
query = (Post
.select(Post, first_tag.alias('first_tag'))
.order_by(first_tag))
set(value[, as_json=None])
Parameters
• value -- a scalar value, list, or dictionary.
• as_json (bool) -- force the value to be treated as JSON, in which case it will be
serialized as JSON in Python beforehand. By default, lists and dictionaries are
treated as JSON to be serialized, while strings and integers are passed as-is.
Set the value at the given location in the JSON data.
Uses the json_set() function from the json1 extension.
update(data)
Parameters
data -- a scalar value, list or dictionary to merge with the data at the given
location in the JSON data. To remove a particular key, set that key to None in the
updated data.
Merge new data into the JSON value using the RFC-7396 MergePatch algorithm to apply a patch
(data parameter) against the column data. MergePatch can add, modify, or delete elements of
a JSON object, which means update() is a generalized replacement for both set() and
remove(). MergePatch treats JSON array objects as atomic, so update() cannot append to an
array, nor modify individual elements of an array.
For more information as well as examples, see the SQLite json_patch() function
documentation.
remove()
Remove the data stored in at the given location in the JSON data.
Uses the json_type function from the json1 extension.
json_type()
Return a string identifying the type of value stored at the given location in the JSON
data.
The type returned will be one of:
• object
• array
• integer
• real
• true
• false
• text
• null <-- the string "null" means an actual NULL value
• NULL <-- an actual NULL value means the path was not found
Uses the json_type function from the json1 extension.
length()
Return the length of the array stored at the given location in the JSON data.
Uses the json_array_length function from the json1 extension.
children()
Table-valued function that exposes the direct descendants of a JSON object at the given
location. See also JSONField.children().
tree() Table-valued function that exposes all descendants, recursively, of a JSON object at the
given location. See also JSONField.tree().
class SearchField([unindexed=False[, column_name=None]])
Field-class to be used for columns on models representing full-text search virtual tables. The
full-text search extensions prohibit the specification of any typing or constraints on columns.
This behavior is enforced by the SearchField, which raises an exception if any configuration is
attempted that would be incompatible with the full-text search extensions.
Example model for document search index (timestamp is stored in the table but it's data is not
searchable):
class DocumentIndex(FTSModel):
title = SearchField()
content = SearchField()
tags = SearchField()
timestamp = SearchField(unindexed=True)
class VirtualModel
Model class designed to be used to represent virtual tables. The default metadata settings are
slightly different, to match those frequently used by virtual tables.
Metadata options:
• arguments - arguments passed to the virtual table constructor.
• extension_module - name of extension to use for virtual table.
•
options - a dictionary of settings to apply in virtual table
constructor.
• primary_key - defaults to False, indicating no primary key.
These all are combined in the following way:
CREATE VIRTUAL TABLE <table_name>
USING <extension_module>
([prefix_arguments, ...] fields, ... [arguments, ...], [options...])
class FTSModel
Subclass of VirtualModel to be used with the FTS3 and FTS4 full-text search extensions.
FTSModel subclasses should be defined normally, however there are a couple caveats:
• Unique constraints, not null constraints, check constraints and foreign keys are not supported.
• Indexes on fields and multi-column indexes are ignored completely
• Sqlite will treat all column types as TEXT (although you can store other data types, Sqlite will
treat them as text).
• FTS models contain a rowid field which is automatically created and managed by SQLite (unless
you choose to explicitly set it during model creation). Lookups on this column are fast and
efficient.
Given these constraints, it is strongly recommended that all fields declared on an FTSModel
subclass be instances of SearchField (though an exception is made for explicitly declaring a
RowIDField). Using SearchField will help prevent you accidentally creating invalid column
constraints. If you wish to store metadata in the index but would not like it to be included in
the full-text index, then specify unindexed=True when instantiating the SearchField.
The only exception to the above is for the rowid primary key, which can be declared using
RowIDField. Lookups on the rowid are very efficient. If you are using FTS4 you can also use
DocIDField, which is an alias for the rowid (though there is no benefit to doing so).
Because of the lack of secondary indexes, it usually makes sense to use the rowid primary key as a
pointer to a row in a regular table. For example:
class Document(Model):
# Canonical source of data, stored in a regular table.
author = ForeignKeyField(User, backref='documents')
title = TextField(null=False, unique=True)
content = TextField(null=False)
timestamp = DateTimeField()
class Meta:
database = db
class DocumentIndex(FTSModel):
# Full-text search index.
rowid = RowIDField()
title = SearchField()
content = SearchField()
class Meta:
database = db
# Use the porter stemming algorithm to tokenize content.
options = {'tokenize': 'porter'}
To store a document in the document index, we will INSERT a row into the DocumentIndex table,
manually setting the rowid so that it matches the primary-key of the corresponding Document:
def store_document(document):
DocumentIndex.insert({
DocumentIndex.rowid: document.id,
DocumentIndex.title: document.title,
DocumentIndex.content: document.content}).execute()
To perform a search and return ranked results, we can query the Document table and join on the
DocumentIndex. This join will be efficient because lookups on an FTSModel's rowid field are fast:
def search(phrase):
# Query the search index and join the corresponding Document
# object on each search result.
return (Document
.select()
.join(
DocumentIndex,
on=(Document.id == DocumentIndex.rowid))
.where(DocumentIndex.match(phrase))
.order_by(DocumentIndex.bm25()))
WARNING:
All SQL queries on FTSModel classes will be full-table scans except full-text searches and
rowid lookups.
If the primary source of the content you are indexing exists in a separate table, you can save
some disk space by instructing SQLite to not store an additional copy of the search index content.
SQLite will still create the metadata and data-structures needed to perform searches on the
content, but the content itself will not be stored in the search index.
To accomplish this, you can specify a table or column using the content option. The FTS4
documentation has more information.
Here is a short example illustrating how to implement this with peewee:
class Blog(Model):
title = TextField()
pub_date = DateTimeField(default=datetime.datetime.now)
content = TextField() # We want to search this.
class Meta:
database = db
class BlogIndex(FTSModel):
content = SearchField()
class Meta:
database = db
options = {'content': Blog.content} # <-- specify data source.
db.create_tables([Blog, BlogIndex])
# Now, we can manage content in the BlogIndex. To populate the
# search index:
BlogIndex.rebuild()
# Optimize the index.
BlogIndex.optimize()
The content option accepts either a single Field or a Model and can reduce the amount of storage
used by the database file. However, content will need to be manually moved to/from the associated
FTSModel.
classmethod match(term)
Parameters
term -- Search term or expression.
Generate a SQL expression representing a search for the given term or expression in the
table. SQLite uses the MATCH operator to indicate a full-text search.
Example:
# Search index for "search phrase" and return results ranked
# by relevancy using the BM25 algorithm.
query = (DocumentIndex
.select()
.where(DocumentIndex.match('search phrase'))
.order_by(DocumentIndex.bm25()))
for result in query:
print('Result: %s' % result.title)
classmethod search(term[, weights=None[, with_score=False[, score_alias='score'[,
explicit_ordering=False]]]])
Parameters
• term (str) -- Search term to use.
• weights -- A list of weights for the columns, ordered with respect to the column's
position in the table. Or, a dictionary keyed by the field or field name and
mapped to a value.
• with_score -- Whether the score should be returned as part of the SELECT
statement.
• score_alias (str) -- Alias to use for the calculated rank score. This is the
attribute you will use to access the score if with_score=True.
• explicit_ordering (bool) -- Order using full SQL function to calculate rank, as
opposed to simply referencing the score alias in the ORDER BY clause.
Shorthand way of searching for a term and sorting results by the quality of the match.
NOTE:
This method uses a simplified algorithm for determining the relevance rank of results.
For more sophisticated result ranking, use the search_bm25() method.
# Simple search.
docs = DocumentIndex.search('search term')
for result in docs:
print(result.title)
# More complete example.
docs = DocumentIndex.search(
'search term',
weights={'title': 2.0, 'content': 1.0},
with_score=True,
score_alias='search_score')
for result in docs:
print(result.title, result.search_score)
classmethod search_bm25(term[, weights=None[, with_score=False[, score_alias='score'[,
explicit_ordering=False]]]])
Parameters
• term (str) -- Search term to use.
• weights -- A list of weights for the columns, ordered with respect to the column's
position in the table. Or, a dictionary keyed by the field or field name and
mapped to a value.
• with_score -- Whether the score should be returned as part of the SELECT
statement.
• score_alias (str) -- Alias to use for the calculated rank score. This is the
attribute you will use to access the score if with_score=True.
• explicit_ordering (bool) -- Order using full SQL function to calculate rank, as
opposed to simply referencing the score alias in the ORDER BY clause.
Shorthand way of searching for a term and sorting results by the quality of the match using
the BM25 algorithm.
ATTENTION:
The BM25 ranking algorithm is only available for FTS4. If you are using FTS3, use the
search() method instead.
classmethod search_bm25f(term[, weights=None[, with_score=False[, score_alias='score'[,
explicit_ordering=False]]]])
Same as FTSModel.search_bm25(), but using the BM25f variant of the BM25 ranking algorithm.
classmethod search_lucene(term[, weights=None[, with_score=False[, score_alias='score'[,
explicit_ordering=False]]]])
Same as FTSModel.search_bm25(), but using the result ranking algorithm from the Lucene
search engine.
classmethod rank([col1_weight, col2_weight...coln_weight])
Parameters
col_weight (float) -- (Optional) weight to give to the ith column of the model. By
default all columns have a weight of 1.0.
Generate an expression that will calculate and return the quality of the search match. This
rank can be used to sort the search results. A higher rank score indicates a better match.
The rank function accepts optional parameters that allow you to specify weights for the
various columns. If no weights are specified, all columns are considered of equal
importance.
NOTE:
The algorithm used by rank() is simple and relatively quick. For more sophisticated
result ranking, use:
• bm25()
• bm25f()
• lucene()
query = (DocumentIndex
.select(
DocumentIndex,
DocumentIndex.rank().alias('score'))
.where(DocumentIndex.match('search phrase'))
.order_by(DocumentIndex.rank()))
for search_result in query:
print search_result.title, search_result.score
classmethod bm25([col1_weight, col2_weight...coln_weight])
Parameters
col_weight (float) -- (Optional) weight to give to the ith column of the model. By
default all columns have a weight of 1.0.
Generate an expression that will calculate and return the quality of the search match using
the BM25 algorithm. This value can be used to sort the search results, with higher scores
corresponding to better matches.
Like rank(), bm25 function accepts optional parameters that allow you to specify weights
for the various columns. If no weights are specified, all columns are considered of equal
importance.
ATTENTION:
The BM25 result ranking algorithm requires FTS4. If you are using FTS3, use rank()
instead.
query = (DocumentIndex
.select(
DocumentIndex,
DocumentIndex.bm25().alias('score'))
.where(DocumentIndex.match('search phrase'))
.order_by(DocumentIndex.bm25()))
for search_result in query:
print(search_result.title, search_result.score)
NOTE:
The above code example is equivalent to calling the search_bm25() method:
query = DocumentIndex.search_bm25('search phrase', with_score=True)
for search_result in query:
print(search_result.title, search_result.score)
classmethod bm25f([col1_weight, col2_weight...coln_weight])
Identical to bm25(), except that it uses the BM25f variant of the BM25 ranking algorithm.
classmethod lucene([col1_weight, col2_weight...coln_weight])
Identical to bm25(), except that it uses the Lucene search result ranking algorithm.
classmethod rebuild()
Rebuild the search index -- this only works when the content option was specified during
table creation.
classmethod optimize()
Optimize the search index.
class FTS5Model
Subclass of VirtualModel to be used with the FTS5 full-text search extensions.
FTS5Model subclasses should be defined normally, however there are a couple caveats:
• FTS5 explicitly disallows specification of any constraints, data-type or indexes on columns. For
that reason, all columns must be instances of SearchField.
• FTS5 models contain a rowid field which is automatically created and managed by SQLite (unless
you choose to explicitly set it during model creation). Lookups on this column are fast and
efficient.
• Indexes on fields and multi-column indexes are not supported.
The FTS5 extension comes with a built-in implementation of the BM25 ranking function. Therefore,
the search and search_bm25 methods have been overridden to use the builtin ranking functions
rather than user-defined functions.
classmethod fts5_installed()
Return a boolean indicating whether the FTS5 extension is installed. If it is not
installed, an attempt will be made to load the extension.
classmethod search(term[, weights=None[, with_score=False[, score_alias='score']]])
Parameters
• term (str) -- Search term to use.
• weights -- A list of weights for the columns, ordered with respect to the column's
position in the table. Or, a dictionary keyed by the field or field name and
mapped to a value.
• with_score -- Whether the score should be returned as part of the SELECT
statement.
• score_alias (str) -- Alias to use for the calculated rank score. This is the
attribute you will use to access the score if with_score=True.
• explicit_ordering (bool) -- Order using full SQL function to calculate rank, as
opposed to simply referencing the score alias in the ORDER BY clause.
Shorthand way of searching for a term and sorting results by the quality of the match. The
FTS5 extension provides a built-in implementation of the BM25 algorithm, which is used to
rank the results by relevance.
Higher scores correspond to better matches.
# Simple search.
docs = DocumentIndex.search('search term')
for result in docs:
print(result.title)
# More complete example.
docs = DocumentIndex.search(
'search term',
weights={'title': 2.0, 'content': 1.0},
with_score=True,
score_alias='search_score')
for result in docs:
print(result.title, result.search_score)
classmethod search_bm25(term[, weights=None[, with_score=False[, score_alias='score']]])
With FTS5, search_bm25() is identical to the search() method.
classmethod rank([col1_weight, col2_weight...coln_weight])
Parameters
col_weight (float) -- (Optional) weight to give to the ith column of the model. By
default all columns have a weight of 1.0.
Generate an expression that will calculate and return the quality of the search match using
the BM25 algorithm. This value can be used to sort the search results, with higher scores
corresponding to better matches.
The rank() function accepts optional parameters that allow you to specify weights for the
various columns. If no weights are specified, all columns are considered of equal
importance.
query = (DocumentIndex
.select(
DocumentIndex,
DocumentIndex.rank().alias('score'))
.where(DocumentIndex.match('search phrase'))
.order_by(DocumentIndex.rank()))
for search_result in query:
print(search_result.title, search_result.score)
NOTE:
The above code example is equivalent to calling the search() method:
query = DocumentIndex.search('search phrase', with_score=True)
for search_result in query:
print(search_result.title, search_result.score)
classmethod bm25([col1_weight, col2_weight...coln_weight])
Because FTS5 provides built-in support for BM25, the bm25() method is identical to the
rank() method.
classmethod VocabModel([table_type='row'|'col'|'instance'[, table_name=None]])
Parameters
• table_type (str) -- Either 'row', 'col' or 'instance'.
• table_name -- Name for the vocab table. If not specified, will be
"fts5tablename_v".
Generate a model class suitable for accessing the vocab table corresponding to FTS5 search
index.
class TableFunction
Implement a user-defined table-valued function. Unlike a simple scalar or aggregate function,
which returns a single scalar value, a table-valued function can return any number of rows of
tabular data.
Simple example:
from playhouse.sqlite_ext import TableFunction
class Series(TableFunction):
# Name of columns in each row of generated data.
columns = ['value']
# Name of parameters the function may be called with.
params = ['start', 'stop', 'step']
def initialize(self, start=0, stop=None, step=1):
"""
Table-functions declare an initialize() method, which is
called with whatever arguments the user has called the
function with.
"""
self.start = self.current = start
self.stop = stop or float('Inf')
self.step = step
def iterate(self, idx):
"""
Iterate is called repeatedly by the SQLite database engine
until the required number of rows has been read **or** the
function raises a `StopIteration` signalling no more rows
are available.
"""
if self.current > self.stop:
raise StopIteration
ret, self.current = self.current, self.current + self.step
return (ret,)
# Register the table-function with our database, which ensures it
# is declared whenever a connection is opened.
db.table_function('series')(Series)
# Usage:
cursor = db.execute_sql('SELECT * FROM series(?, ?, ?)', (0, 5, 2))
for value, in cursor:
print(value)
NOTE:
A TableFunction must be registered with a database connection before it can be used. To ensure
the table function is always available, you can use the SqliteDatabase.table_function()
decorator to register the function with the database.
TableFunction implementations must provide two attributes and implement two methods, described
below.
columns
A list containing the names of the columns for the data returned by the function. For
example, a function that is used to split a string on a delimiter might specify 3 columns:
[substring, start_idx, end_idx].
params The names of the parameters the function may be called with. All parameters, including
optional parameters, should be listed. For example, a function that is used to split a
string on a delimiter might specify 2 params: [string, delimiter].
name Optional - specify the name for the table function. If not provided, name will be taken
from the class name.
print_tracebacks = True
Print a full traceback for any errors that occur in the table-function's callback methods.
When set to False, only the generic OperationalError will be visible.
initialize(**parameter_values)
Parameters
parameter_values -- Parameters the function was called with.
Returns
No return value.
The initialize method is called to initialize the table function with the parameters the
user specified when calling the function.
iterate(idx)
Parameters
idx (int) -- current iteration step
Returns
A tuple of row data corresponding to the columns named in the columns attribute.
Raises StopIteration -- To signal that no more rows are available.
This function is called repeatedly and returns successive rows of data. The function may
terminate before all rows are consumed (especially if the user specified a LIMIT on the
results). Alternatively, the function can signal that no more data is available by raising
a StopIteration exception.
classmethod register(conn)
Parameters
conn -- A sqlite3.Connection object.
Register the table function with a DB-API 2.0 sqlite3.Connection object. Table-valued
functions must be registered before they can be used in a query.
Example:
class MyTableFunction(TableFunction):
name = 'my_func'
# ... other attributes and methods ...
db = SqliteDatabase(':memory:')
db.connect()
MyTableFunction.register(db.connection())
To ensure the TableFunction is registered every time a connection is opened, use the
table_function() decorator.
ClosureTable(model_class[, foreign_key=None[, referencing_class=None[, referencing_key=None]]])
Parameters
• model_class -- The model class containing the nodes in the tree.
• foreign_key -- The self-referential parent-node field on the model class. If not
provided, peewee will introspect the model to find a suitable key.
• referencing_class -- Intermediate table for a many-to-many relationship.
• referencing_key -- For a many-to-many relationship, the originating side of the relation.
Returns
Returns a VirtualModel for working with a closure table.
Factory function for creating a model class suitable for working with a transitive closure table.
Closure tables are VirtualModel subclasses that work with the transitive closure SQLite extension.
These special tables are designed to make it easy to efficiently query hierarchical data. The
SQLite extension manages an AVL tree behind-the-scenes, transparently updating the tree when your
table changes and making it easy to perform common queries on hierarchical data.
To use the closure table extension in your project, you need:
1. A copy of the SQLite extension. The source code can be found in the SQLite code repository or
by cloning this gist:
$ git clone https://gist.github.com/coleifer/7f3593c5c2a645913b92 closure
$ cd closure/
2. Compile the extension as a shared library, e.g.
$ gcc -g -fPIC -shared closure.c -o closure.so
3. Create a model for your hierarchical data. The only requirement here is that the model has an
integer primary key and a self-referential foreign key. Any additional fields are fine.
class Category(Model):
name = CharField()
metadata = TextField()
parent = ForeignKeyField('self', index=True, null=True) # Required.
# Generate a model for the closure virtual table.
CategoryClosure = ClosureTable(Category)
The self-referentiality can also be achieved via an intermediate table (for a many-to-many
relation).
class User(Model):
name = CharField()
class UserRelations(Model):
user = ForeignKeyField(User)
knows = ForeignKeyField(User, backref='_known_by')
class Meta:
primary_key = CompositeKey('user', 'knows') # Alternatively, a unique index on both columns.
# Generate a model for the closure virtual table, specifying the UserRelations as the referencing table
UserClosure = ClosureTable(
User,
referencing_class=UserRelations,
foreign_key=UserRelations.knows,
referencing_key=UserRelations.user)
4. In your application code, make sure you load the extension when you instantiate your Database
object. This is done by passing the path to the shared library to the load_extension() method.
db = SqliteExtDatabase('my_database.db')
db.load_extension('/path/to/closure')
WARNING:
There are two caveats you should be aware of when using the transitive_closure extension.
First, it requires that your source model have an integer primary key. Second, it is strongly
recommended that you create an index on the self-referential foreign key.
Example:
class Category(Model):
name = CharField()
metadata = TextField()
parent = ForeignKeyField('self', index=True, null=True) # Required.
# Generate a model for the closure virtual table.
CategoryClosure = ClosureTable(Category)
# Create the tables if they do not exist.
db.create_tables([Category, CategoryClosure], True)
It is now possible to perform interesting queries using the data from the closure table:
# Get all ancestors for a particular node.
laptops = Category.get(Category.name == 'Laptops')
for parent in Closure.ancestors(laptops):
print parent.name
# Computer Hardware
# Computers
# Electronics
# All products
# Get all descendants for a particular node.
hardware = Category.get(Category.name == 'Computer Hardware')
for node in Closure.descendants(hardware):
print node.name
# Laptops
# Desktops
# Hard-drives
# Monitors
# LCD Monitors
# LED Monitors
API of the VirtualModel returned by ClosureTable().
class BaseClosureTable
id A field for the primary key of the given node.
depth A field representing the relative depth of the given node.
root A field representing the relative root node.
descendants(node[, depth=None[, include_node=False]])
Retrieve all descendants of the given node. If a depth is specified, only nodes at
that depth (relative to the given node) will be returned.
node = Category.get(Category.name == 'Electronics')
# Direct child categories.
children = CategoryClosure.descendants(node, depth=1)
# Grand-child categories.
children = CategoryClosure.descendants(node, depth=2)
# Descendants at all depths.
all_descendants = CategoryClosure.descendants(node)
ancestors(node[, depth=None[, include_node=False]])
Retrieve all ancestors of the given node. If a depth is specified, only nodes at
that depth (relative to the given node) will be returned.
node = Category.get(Category.name == 'Laptops')
# All ancestors.
all_ancestors = CategoryClosure.ancestors(node)
# Grand-parent category.
grandparent = CategoryClosure.ancestores(node, depth=2)
siblings(node[, include_node=False])
Retrieve all nodes that are children of the specified node's parent.
NOTE:
For an in-depth discussion of the SQLite transitive closure extension, check out this blog
post, Querying Tree Structures in SQLite using Python and the Transitive Closure Extension.
class LSMTable
VirtualModel subclass suitable for working with the lsm1 extension The lsm1 extension is a virtual
table that provides a SQL interface to the lsm key/value storage engine from SQLite4.
NOTE:
The LSM1 extension has not been released yet (SQLite version 3.22 at time of writing), so
consider this feature experimental with potential to change in subsequent releases.
LSM tables define one primary key column and an arbitrary number of additional value columns
(which are serialized and stored in a single value field in the storage engine). The primary key
must be all of the same type and use one of the following field types:
• IntegerField
• TextField
• BlobField
Since the LSM storage engine is a key/value store, primary keys (including integers) must be
specified by the application.
ATTENTION:
Secondary indexes are not supported by the LSM engine, so the only efficient queries will be
lookups (or range queries) on the primary key. Other fields can be queried and filtered on,
but may result in a full table-scan.
Example model declaration:
db = SqliteExtDatabase('my_app.db')
db.load_extension('lsm.so') # Load shared library.
class EventLog(LSMTable):
timestamp = IntegerField(primary_key=True)
action = TextField()
sender = TextField()
target = TextField()
class Meta:
database = db
filename = 'eventlog.ldb' # LSM data is stored in separate db.
# Declare virtual table.
EventLog.create_table()
Example queries:
# Use dictionary operators to get, set and delete rows from the LSM
# table. Slices may be passed to represent a range of key values.
def get_timestamp():
# Return time as integer expressing time in microseconds.
return int(time.time() * 1000000)
# Create a new row, at current timestamp.
ts = get_timestamp()
EventLog[ts] = ('pageview', 'search', '/blog/some-post/')
# Retrieve row from event log.
log = EventLog[ts]
print(log.action, log.sender, log.target)
# Prints ("pageview", "search", "/blog/some-post/")
# Delete the row.
del EventLog[ts]
# We can also use the "create()" method.
EventLog.create(
timestamp=get_timestamp(),
action='signup',
sender='newsletter',
target='sqlite-news')
Simple key/value model declaration:
class KV(LSMTable):
key = TextField(primary_key=True)
value = TextField()
class Meta:
database = db
filename = 'kv.ldb'
db.create_tables([KV])
For tables consisting of a single value field, Peewee will return the value directly when getting
a single item. You can also request slices of rows, in which case Peewee returns a corresponding
Select query, which can be iterated over. Below are some examples:
>>> KV['k0'] = 'v0'
>>> print(KV['k0'])
'v0'
>>> data = [{'key': 'k%d' % i, 'value': 'v%d' % i} for i in range(20)]
>>> KV.insert_many(data).execute()
>>> KV.select().count()
20
>>> KV['k8']
'v8'
>>> list(KV['k4.1':'k7.x']
[Row(key='k5', value='v5'),
Row(key='k6', value='v6'),
Row(key='k7', value='v7')]
>>> list(KV['k6xxx':])
[Row(key='k7', value='v7'),
Row(key='k8', value='v8'),
Row(key='k9', value='v9')]
You can also index the LSMTable using expressions:
>>> list(KV[KV.key > 'k6'])
[Row(key='k7', value='v7'),
Row(key='k8', value='v8'),
Row(key='k9', value='v9')]
>>> list(KV[(KV.key > 'k6') & (KV.value != 'v8')])
[Row(key='k7', value='v7'),
Row(key='k9', value='v9')]
You can delete single rows using del or multiple rows using slices or expressions:
>>> del KV['k1']
>>> del KV['k3x':'k8']
>>> del KV[KV.key.between('k10', 'k18')]
>>> list(KV[:])
[Row(key='k0', value='v0'),
Row(key='k19', value='v19'),
Row(key='k2', value='v2'),
Row(key='k3', value='v3'),
Row(key='k9', value='v9')]
Attempting to get a single non-existant key will result in a KeyError, but slices will not raise
an exception:
>>> KV['k1']
...
KeyError: 'k1'
>>> list(KV['k1':'k1'])
[]
class ZeroBlob(length)
Parameters
length (int) -- Size of blob in bytes.
ZeroBlob is used solely to reserve space for storing a BLOB that supports incremental I/O. To use
the SQLite BLOB-store it is necessary to first insert a ZeroBlob of the desired size into the row
you wish to use with incremental I/O.
For example, see Blob.
class Blob(database, table, column, rowid[, read_only=False])
Parameters
• database -- SqliteExtDatabase instance.
• table (str) -- Name of table being accessed.
• column (str) -- Name of column being accessed.
• rowid (int) -- Primary-key of row being accessed.
• read_only (bool) -- Prevent any modifications to the blob data.
Open a blob, stored in the given table/column/row, for incremental I/O. To allocate storage for
new data, you can use the ZeroBlob, which is very efficient.
class RawData(Model):
data = BlobField()
# Allocate 100MB of space for writing a large file incrementally:
query = RawData.insert({'data': ZeroBlob(1024 * 1024 * 100)})
rowid = query.execute()
# Now we can open the row for incremental I/O:
blob = Blob(db, 'rawdata', 'data', rowid)
# Read from the file and write to the blob in chunks of 4096 bytes.
while True:
data = file_handle.read(4096)
if not data:
break
blob.write(data)
bytes_written = blob.tell()
blob.close()
read([n=None])
Parameters
n (int) -- Only read up to n bytes from current position in file.
Read up to n bytes from the current position in the blob file. If n is not specified, the
entire blob will be read.
seek(offset[, whence=0])
Parameters
• offset (int) -- Seek to the given offset in the file.
• whence (int) -- Seek relative to the specified frame of reference.
Values for whence:
• 0: beginning of file
• 1: current position
• 2: end of file
tell() Return current offset within the file.
write(data)
Parameters
data (bytes) -- Data to be written
Writes the given data, starting at the current position in the file.
close()
Close the file and free associated resources.
reopen(rowid)
Parameters
rowid (int) -- Primary key of row to open.
If a blob has already been opened for a given table/column, you can use the reopen() method
to re-use the same Blob object for accessing multiple rows in the table.
Additional Features
The SqliteExtDatabase accepts an initialization option to register support for a simple bloom filter.
The bloom filter, once initialized, can then be used for efficient membership queries on large set of
data.
Here's an example:
db = CSqliteExtDatabase(':memory:', bloomfilter=True)
# Create and define a table to store some data.
db.execute_sql('CREATE TABLE "register" ("data" TEXT)')
Register = Table('register', ('data',)).bind(db)
# Populate the database with a bunch of text.
with db.atomic():
for i in 'abcdefghijklmnopqrstuvwxyz':
keys = [i * j for j in range(1, 10)] # a, aa, aaa, ... aaaaaaaaa
Register.insert([{'data': key} for key in keys]).execute()
# Collect data into a 16KB bloomfilter.
query = Register.select(fn.bloomfilter(Register.data, 16 * 1024).alias('buf'))
row = query.get()
buf = row['buf']
# Use bloomfilter buf to test whether other keys are members.
test_keys = (
('aaaa', True),
('abc', False),
('zzzzzzz', True),
('zyxwvut', False))
for key, is_present in test_keys:
query = Register.select(fn.bloomfilter_contains(key, buf).alias('is_member'))
answer = query.get()['is_member']
assert answer == is_present
The SqliteExtDatabase can also register other useful functions:
• rank_functions (enabled by default): registers functions for ranking search results, such as bm25 and
lucene.
• hash_functions: registers md5, sha1, sha256, adler32, crc32 and murmurhash functions.
• regexp_function: registers a regexp function.
Examples:
def create_new_user(username, password):
# DO NOT DO THIS IN REAL LIFE. PLEASE.
query = User.insert({'username': username, 'password': fn.sha1(password)})
new_user_id = query.execute()
You can use the murmurhash function to hash bytes to an integer for compact storage:
>>> db = SqliteExtDatabase(':memory:', hash_functions=True)
>>> db.execute_sql('SELECT murmurhash(?)', ('abcdefg',)).fetchone()
(4188131059,)
Playhouse, extensions to Peewee
Peewee comes with numerous extension modules which are collected under the playhouse namespace. Despite
the silly name, there are some very useful extensions, particularly those that expose vendor-specific
database features like the sqlite_ext and Postgresql Extensions extensions.
Below you will find a loosely organized listing of the various modules that make up the playhouse.
Database drivers / vendor-specific database functionality
• sqlite_ext (on its own page)
• SqliteQ
• Sqlite User-Defined Functions
• apsw, an advanced sqlite driver
• Sqlcipher backend
• Postgresql Extensions
• MySQL Extensions
High-level features
• Fields
• Shortcuts
• Hybrid Attributes
• Key/Value Store
• Signal support
• DataSet
Database management and framework integration
• pwiz, a model generator
• Schema Migrations
• Connection pool
• Reflection
• Database URL
• Test Utils
• Flask Utils
Sqlite Extensions
The Sqlite extensions have been moved to their own page.
SqliteQ
The playhouse.sqliteq module provides a subclass of SqliteExtDatabase, that will serialize concurrent
writes to a SQLite database. SqliteQueueDatabase can be used as a drop-in replacement for the regular
SqliteDatabase if you want simple read and write access to a SQLite database from multiple threads.
SQLite only allows one connection to write to the database at any given time. As a result, if you have a
multi-threaded application (like a web-server, for example) that needs to write to the database, you may
see occasional errors when one or more of the threads attempting to write cannot acquire the lock.
SqliteQueueDatabase is designed to simplify things by sending all write queries through a single,
long-lived connection. The benefit is that you get the appearance of multiple threads writing to the
database without conflicts or timeouts. The downside, however, is that you cannot issue write
transactions that encompass multiple queries -- all writes run in autocommit mode, essentially.
NOTE:
The module gets its name from the fact that all write queries get put into a thread-safe queue. A
single worker thread listens to the queue and executes all queries that are sent to it.
Transactions
Because all queries are serialized and executed by a single worker thread, it is possible for
transactional SQL from separate threads to be executed out-of-order. In the example below, the
transaction started by thread "B" is rolled back by thread "A" (with bad consequences!):
• Thread A: UPDATE transplants SET organ='liver', ...;
• Thread B: BEGIN TRANSACTION;
• Thread B: UPDATE life_support_system SET timer += 60 ...;
• Thread A: ROLLBACK; -- Oh no....
Since there is a potential for queries from separate transactions to be interleaved, the transaction()
and atomic() methods are disabled on SqliteQueueDatabase.
For cases when you wish to temporarily write to the database from a different thread, you can use the
pause() and unpause() methods. These methods block the caller until the writer thread is finished with
its current workload. The writer then disconnects and the caller takes over until unpause is called.
The stop(), start(), and is_stopped() methods can also be used to control the writer thread.
NOTE:
Take a look at SQLite's isolation documentation for more information about how SQLite handles
concurrent connections.
Code sample
Creating a database instance does not require any special handling. The SqliteQueueDatabase accepts some
special parameters which you should be aware of, though. If you are using gevent, you must specify
use_gevent=True when instantiating your database -- this way Peewee will know to use the appropriate
objects for handling queueing, thread creation, and locking.
from playhouse.sqliteq import SqliteQueueDatabase
db = SqliteQueueDatabase(
'my_app.db',
use_gevent=False, # Use the standard library "threading" module.
autostart=False, # The worker thread now must be started manually.
queue_max_size=64, # Max. # of pending writes that can accumulate.
results_timeout=5.0) # Max. time to wait for query to be executed.
If autostart=False, as in the above example, you will need to call start() to bring up the worker threads
that will do the actual write query execution.
@app.before_first_request
def _start_worker_threads():
db.start()
If you plan on performing SELECT queries or generally wanting to access the database, you will need to
call connect() and close() as you would with any other database instance.
When your application is ready to terminate, use the stop() method to shut down the worker thread. If
there was a backlog of work, then this method will block until all pending work is finished (though no
new work is allowed).
import atexit
@atexit.register
def _stop_worker_threads():
db.stop()
Lastly, the is_stopped() method can be used to determine whether the database writer is up and running.
Sqlite User-Defined Functions
The sqlite_udf playhouse module contains a number of user-defined functions, aggregates, and table-valued
functions, which you may find useful. The functions are grouped in collections and you can register
these user-defined extensions individually, by collection, or register everything.
Scalar functions are functions which take a number of parameters and return a single value. For example,
converting a string to upper-case, or calculating the MD5 hex digest.
Aggregate functions are like scalar functions that operate on multiple rows of data, producing a single
result. For example, calculating the sum of a list of integers, or finding the smallest value in a
particular column.
Table-valued functions are simply functions that can return multiple rows of data. For example, a
regular-expression search function that returns all the matches in a given string, or a function that
accepts two dates and generates all the intervening days.
NOTE:
To use table-valued functions, you will need to build the playhouse._sqlite_ext C extension.
Registering user-defined functions:
db = SqliteDatabase('my_app.db')
# Register *all* functions.
register_all(db)
# Alternatively, you can register individual groups. This will just
# register the DATE and MATH groups of functions.
register_groups(db, 'DATE', 'MATH')
# If you only wish to register, say, the aggregate functions for a
# particular group or groups, you can:
register_aggregate_groups(db, 'DATE')
Using a library function ("hostname"):
# Assume we have a model, Link, that contains lots of arbitrary URLs.
# We want to discover the most common hosts that have been linked.
query = (Link
.select(fn.hostname(Link.url).alias('host'), fn.COUNT(Link.id))
.group_by(fn.hostname(Link.url))
.order_by(fn.COUNT(Link.id).desc())
.tuples())
# Print the hostname along with number of links associated with it.
for host, count in query:
print('%s: %s' % (host, count))
Functions, listed by collection name
Scalar functions are indicated by (f), aggregate functions by (a), and table-valued functions by (t).
CONTROL_FLOW
if_then_else(cond, truthy[, falsey=None])
Simple ternary-type operator, where, depending on the truthiness of the cond parameter, either the
truthy or falsey value will be returned.
DATE
strip_tz(date_str)
Parameters
date_str -- A datetime, encoded as a string.
Returns
The datetime with any timezone info stripped off.
The time is not adjusted in any way, the timezone is simply removed.
humandelta(nseconds[, glue=', '])
Parameters
• nseconds (int) -- Number of seconds, total, in timedelta.
• glue (str) -- Fragment to join values.
Returns
Easy-to-read description of timedelta.
Example, 86471 -> "1 day, 1 minute, 11 seconds"
mintdiff(datetime_value)
Parameters
datetime_value -- A date-time.
Returns
Minimum difference between any two values in list.
Aggregate function that computes the minimum difference between any two datetimes.
avgtdiff(datetime_value)
Parameters
datetime_value -- A date-time.
Returns
Average difference between values in list.
Aggregate function that computes the average difference between consecutive values in the list.
duration(datetime_value)
Parameters
datetime_value -- A date-time.
Returns
Duration from smallest to largest value in list, in seconds.
Aggregate function that computes the duration from the smallest to the largest value in the list,
returned in seconds.
date_series(start, stop[, step_seconds=86400])
Parameters
• start (datetime) -- Start datetime
• stop (datetime) -- Stop datetime
• step_seconds (int) -- Number of seconds comprising a step.
Table-value function that returns rows consisting of the date/+time values encountered iterating
from start to stop, step_seconds at a time.
Additionally, if start does not have a time component and step_seconds is greater-than-or-equal-to
one day (86400 seconds), the values returned will be dates. Conversely, if start does not have a
date component, values will be returned as times. Otherwise values are returned as datetimes.
Example:
SELECT * FROM date_series('2017-01-28', '2017-02-02');
value
-----
2017-01-28
2017-01-29
2017-01-30
2017-01-31
2017-02-01
2017-02-02
FILE
file_ext(filename)
Parameters
filename (str) -- Filename to extract extension from.
Returns
Returns the file extension, including the leading ".".
file_read(filename)
Parameters
filename (str) -- Filename to read.
Returns
Contents of the file.
HELPER
gzip(data[, compression=9])
Parameters
• data (bytes) -- Data to compress.
• compression (int) -- Compression level (9 is max).
Returns
Compressed binary data.
gunzip(data)
Parameters
data (bytes) -- Compressed data.
Returns
Uncompressed binary data.
hostname(url)
Parameters
url (str) -- URL to extract hostname from.
Returns
hostname portion of URL
toggle(key)
Parameters
key -- Key to toggle.
Toggle a key between True/False state. Example:
>>> toggle('my-key')
True
>>> toggle('my-key')
False
>>> toggle('my-key')
True
setting(key[, value=None])
Parameters
• key -- Key to set/retrieve.
• value -- Value to set.
Returns
Value associated with key.
Store/retrieve a setting in memory and persist during lifetime of application. To get the current
value, only specify the key. To set a new value, call with key and new value.
clear_toggles()
Clears all state associated with the toggle() function.
clear_settings()
Clears all state associated with the setting() function.
MATH
randomrange(start[, stop=None[, step=None]])
Parameters
• start (int) -- Start of range (inclusive)
• end (int) -- End of range(not inclusive)
• step (int) -- Interval at which to return a value.
Return a random integer between [start, end).
gauss_distribution(mean, sigma)
Parameters
• mean (float) -- Mean value
• sigma (float) -- Standard deviation
sqrt(n)
Calculate the square root of n.
tonumber(s)
Parameters
s (str) -- String to convert to number.
Returns
Integer, floating-point or NULL on failure.
mode(val)
Parameters
val -- Numbers in list.
Returns
The mode, or most-common, number observed.
Aggregate function which calculates mode of values.
minrange(val)
Parameters
val -- Value
Returns
Min difference between two values.
Aggregate function which calculates the minimal distance between two numbers in the sequence.
avgrange(val)
Parameters
val -- Value
Returns
Average difference between values.
Aggregate function which calculates the average distance between two consecutive numbers in the
sequence.
range(val)
Parameters
val -- Value
Returns
The range from the smallest to largest value in sequence.
Aggregate function which returns range of values observed.
median(val)
Parameters
val -- Value
Returns
The median, or middle, value in a sequence.
Aggregate function which calculates the middle value in a sequence.
NOTE:
Only available if you compiled the _sqlite_udf extension.
STRING
substr_count(haystack, needle)
Returns number of times needle appears in haystack.
strip_chars(haystack, chars)
Strips any characters in chars from beginning and end of haystack.
damerau_levenshtein_dist(s1, s2)
Computes the edit distance from s1 to s2 using the damerau variant of the levenshtein algorithm.
NOTE:
Only available if you compiled the _sqlite_udf extension.
levenshtein_dist(s1, s2)
Computes the edit distance from s1 to s2 using the levenshtein algorithm.
NOTE:
Only available if you compiled the _sqlite_udf extension.
str_dist(s1, s2)
Computes the edit distance from s1 to s2 using the standard library SequenceMatcher's algorithm.
NOTE:
Only available if you compiled the _sqlite_udf extension.
regex_search(regex, search_string)
Parameters
• regex (str) -- Regular expression
• search_string (str) -- String to search for instances of regex.
Table-value function that searches a string for substrings that match the provided regex. Returns
rows for each match found.
Example:
SELECT * FROM regex_search('\w+', 'extract words, ignore! symbols');
value
-----
extract
words
ignore
symbols
apsw, an advanced sqlite driver
The apsw_ext module contains a database class suitable for use with the apsw sqlite driver.
APSW Project page: https://github.com/rogerbinns/apsw
APSW is a really neat library that provides a thin wrapper on top of SQLite's C interface, making it
possible to use all of SQLite's advanced features.
Here are just a few reasons to use APSW, taken from the documentation:
• APSW gives all functionality of SQLite, including virtual tables, virtual file system, blob i/o,
backups and file control.
• Connections can be shared across threads without any additional locking.
• Transactions are managed explicitly by your code.
• APSW can handle nested transactions.
• Unicode is handled correctly.
• APSW is faster.
For more information on the differences between apsw and pysqlite, check the apsw docs.
How to use the APSWDatabase
from apsw_ext import *
db = APSWDatabase(':memory:')
class BaseModel(Model):
class Meta:
database = db
class SomeModel(BaseModel):
col1 = CharField()
col2 = DateTimeField()
apsw_ext API notes
APSWDatabase extends the SqliteExtDatabase and inherits its advanced features.
class APSWDatabase(database, **connect_kwargs)
Parameters
• database (string) -- filename of sqlite database
• connect_kwargs -- keyword arguments passed to apsw when opening a connection
register_module(mod_name, mod_inst)
Provides a way of globally registering a module. For more information, see the
documentation on virtual tables.
Parameters
• mod_name (string) -- name to use for module
• mod_inst (object) -- an object implementing the Virtual Table interface
unregister_module(mod_name)
Unregister a module.
Parameters
mod_name (string) -- name to use for module
NOTE:
Be sure to use the Field subclasses defined in the apsw_ext module, as they will properly handle
adapting the data types for storage.
For example, instead of using peewee.DateTimeField, be sure you are importing and using
playhouse.apsw_ext.DateTimeField.
Sqlcipher backend
• Although this extention's code is short, it has not been properly peer-reviewed yet and may have
introduced vulnerabilities.
• The code contains minimum values for passphrase length and kdf_iter, as well as a default value for the
later. Do not regard these numbers as advice. Consult the docs at http://sqlcipher.net/sqlcipher-api/
and security experts.
Also note that this code relies on pysqlcipher and sqlcipher, and the code there might have
vulnerabilities as well, but since these are widely used crypto modules, we can expect "short zero days"
there.
sqlcipher_ext API notes
class SqlCipherDatabase(database, passphrase, kdf_iter=64000, **kwargs)
Subclass of SqliteDatabase that stores the database encrypted. Instead of the standard sqlite3
backend, it uses pysqlcipher: a python wrapper for sqlcipher, which -- in turn -- is an encrypted
wrapper around sqlite3, so the API is identical to SqliteDatabase's, except for object
construction parameters:
Parameters
• database -- Path to encrypted database filename to open [or create].
• passphrase -- Database encryption passphrase: should be at least 8 character long (or an
error is raised), but it is strongly advised to enforce better passphrase strength
criteria in your implementation.
• kdf_iter -- [Optional] number of PBKDF2 iterations.
• If the database file doesn't exist, it will be created with encryption by a key derived from
passhprase with kdf_iter PBKDF2 iterations.
• When trying to open an existing database, passhprase and kdf_iter should be identical to the
ones used when it was created.
rekey(passphrase)
Parameters
passphrase (str) -- New passphrase for database.
Change the passphrase for database.
Notes:
• [Hopefully] there's no way to tell whether the passphrase is wrong or the file is corrupt. In both
cases -- the first time we try to access the database -- a DatabaseError error is raised, with the
exact message: "file is encrypted or is not a database".
As mentioned above, this only happens when you access the database, so if you need to know right
away whether the passphrase was correct, you can trigger this check by calling [e.g.] get_tables()
(see example below).
• Most applications can expect failed attempts to open the database (common case: prompting the user
for passphrase), so the database can't be hardwired into the Meta of model classes. To defer
initialization, pass None in to the database.
Example:
db = SqlCipherDatabase(None)
class BaseModel(Model):
"""Parent for all app's models"""
class Meta:
# We won't have a valid db until user enters passhrase.
database = db
# Derive our model subclasses
class Person(BaseModel):
name = TextField(primary_key=True)
right_passphrase = False
while not right_passphrase:
db.init(
'testsqlcipher.db',
passphrase=get_passphrase_from_user())
try: # Actually execute a query against the db to test passphrase.
db.get_tables()
except DatabaseError as exc:
# This error indicates the password was wrong.
if exc.args[0] == 'file is encrypted or is not a database':
tell_user_the_passphrase_was_wrong()
db.init(None) # Reset the db.
else:
raise exc
else:
# The password was correct.
right_passphrase = True
See also: a slightly more elaborate example.
Postgresql Extensions
The postgresql extensions module provides a number of "postgres-only" functions, currently:
• json support, including jsonb for Postgres 9.4.
• hstore support
• server-side cursors
• full-text search
• ArrayField field type, for storing arrays.
• HStoreField field type, for storing key/value pairs.
• IntervalField field type, for storing timedelta objects.
• JSONField field type, for storing JSON data.
• BinaryJSONField field type for the jsonb JSON data type.
• TSVectorField field type, for storing full-text search data.
• DateTimeTZ field type, a timezone-aware datetime field.
In the future I would like to add support for more of postgresql's features. If there is a particular
feature you would like to see added, please open a Github issue.
WARNING:
In order to start using the features described below, you will need to use the extension
PostgresqlExtDatabase class instead of PostgresqlDatabase.
The code below will assume you are using the following database and base model:
from playhouse.postgres_ext import *
ext_db = PostgresqlExtDatabase('peewee_test', user='postgres')
class BaseExtModel(Model):
class Meta:
database = ext_db
JSON Support
peewee has basic support for Postgres' native JSON data type, in the form of JSONField. As of version
2.4.7, peewee also supports the Postgres 9.4 binary json jsonb type, via BinaryJSONField.
WARNING:
Postgres supports a JSON data type natively as of 9.2 (full support in 9.3). In order to use this
functionality you must be using the correct version of Postgres with psycopg2 version 2.5 or greater.
To use BinaryJSONField, which has many performance and querying advantages, you must have Postgres 9.4
or later.
NOTE:
You must be sure your database is an instance of PostgresqlExtDatabase in order to use the JSONField.
Here is an example of how you might declare a model with a JSON field:
import json
import urllib2
from playhouse.postgres_ext import *
db = PostgresqlExtDatabase('my_database')
class APIResponse(Model):
url = CharField()
response = JSONField()
class Meta:
database = db
@classmethod
def request(cls, url):
fh = urllib2.urlopen(url)
return cls.create(url=url, response=json.loads(fh.read()))
APIResponse.create_table()
# Store a JSON response.
offense = APIResponse.request('http://crime-api.com/api/offense/')
booking = APIResponse.request('http://crime-api.com/api/booking/')
# Query a JSON data structure using a nested key lookup:
offense_responses = APIResponse.select().where(
APIResponse.response['meta']['model'] == 'offense')
# Retrieve a sub-key for each APIResponse. By calling .as_json(), the
# data at the sub-key will be returned as Python objects (dicts, lists,
# etc) instead of serialized JSON.
q = (APIResponse
.select(
APIResponse.data['booking']['person'].as_json().alias('person'))
.where(APIResponse.data['meta']['model'] == 'booking'))
for result in q:
print(result.person['name'], result.person['dob'])
The BinaryJSONField works the same and supports the same operations as the regular JSONField, but
provides several additional operations for testing containment. Using the binary json field, you can test
whether your JSON data contains other partial JSON structures (contains(), contains_any(),
contains_all()), or whether it is a subset of a larger JSON document (contained_by()).
For more examples, see the JSONField and BinaryJSONField API documents below.
hstore support
Postgresql hstore is an embedded key/value store. With hstore, you can store arbitrary key/value pairs in
your database alongside structured relational data.
To use hstore, you need to specify an additional parameter when instantiating your PostgresqlExtDatabase:
# Specify "register_hstore=True":
db = PostgresqlExtDatabase('my_db', register_hstore=True)
Currently the postgres_ext module supports the following operations:
• Store and retrieve arbitrary dictionaries
• Filter by key(s) or partial dictionary
• Update/add one or more keys to an existing dictionary
• Delete one or more keys from an existing dictionary
• Select keys, values, or zip keys and values
• Retrieve a slice of keys/values
• Test for the existence of a key
• Test that a key has a non-NULL value
Using hstore
To start with, you will need to import the custom database class and the hstore functions from
playhouse.postgres_ext (see above code snippet). Then, it is as simple as adding a HStoreField to your
model:
class House(BaseExtModel):
address = CharField()
features = HStoreField()
You can now store arbitrary key/value pairs on House instances:
>>> h = House.create(
... address='123 Main St',
... features={'garage': '2 cars', 'bath': '2 bath'})
...
>>> h_from_db = House.get(House.id == h.id)
>>> h_from_db.features
{'bath': '2 bath', 'garage': '2 cars'}
You can filter by individual key, multiple keys or partial dictionary:
>>> query = House.select()
>>> garage = query.where(House.features.contains('garage'))
>>> garage_and_bath = query.where(House.features.contains(['garage', 'bath']))
>>> twocar = query.where(House.features.contains({'garage': '2 cars'}))
Suppose you want to do an atomic update to the house:
>>> new_features = House.features.update({'bath': '2.5 bath', 'sqft': '1100'})
>>> query = House.update(features=new_features)
>>> query.where(House.id == h.id).execute()
1
>>> h = House.get(House.id == h.id)
>>> h.features
{'bath': '2.5 bath', 'garage': '2 cars', 'sqft': '1100'}
Or, alternatively an atomic delete:
>>> query = House.update(features=House.features.delete('bath'))
>>> query.where(House.id == h.id).execute()
1
>>> h = House.get(House.id == h.id)
>>> h.features
{'garage': '2 cars', 'sqft': '1100'}
Multiple keys can be deleted at the same time:
>>> query = House.update(features=House.features.delete('garage', 'sqft'))
You can select just keys, just values, or zip the two:
>>> for h in House.select(House.address, House.features.keys().alias('keys')):
... print(h.address, h.keys)
123 Main St [u'bath', u'garage']
>>> for h in House.select(House.address, House.features.values().alias('vals')):
... print(h.address, h.vals)
123 Main St [u'2 bath', u'2 cars']
>>> for h in House.select(House.address, House.features.items().alias('mtx')):
... print(h.address, h.mtx)
123 Main St [[u'bath', u'2 bath'], [u'garage', u'2 cars']]
You can retrieve a slice of data, for example, all the garage data:
>>> query = House.select(House.address, House.features.slice('garage').alias('garage_data'))
>>> for house in query:
... print(house.address, house.garage_data)
123 Main St {'garage': '2 cars'}
You can check for the existence of a key and filter rows accordingly:
>>> has_garage = House.features.exists('garage')
>>> for house in House.select(House.address, has_garage.alias('has_garage')):
... print(house.address, house.has_garage)
123 Main St True
>>> for house in House.select().where(House.features.exists('garage')):
... print(house.address, house.features['garage']) # <-- just houses w/garage data
123 Main St 2 cars
Interval support
Postgres supports durations through the INTERVAL data-type (docs).
class IntervalField([null=False[, ...]])
Field class capable of storing Python datetime.timedelta instances.
Example:
from datetime import timedelta
from playhouse.postgres_ext import *
db = PostgresqlExtDatabase('my_db')
class Event(Model):
location = CharField()
duration = IntervalField()
start_time = DateTimeField()
class Meta:
database = db
@classmethod
def get_long_meetings(cls):
return cls.select().where(cls.duration > timedelta(hours=1))
Server-side cursors
When psycopg2 executes a query, normally all results are fetched and returned to the client by the
backend. This can cause your application to use a lot of memory when making large queries. Using
server-side cursors, results are returned a little at a time (by default 2000 records). For the
definitive reference, please see the psycopg2 documentation.
NOTE:
To use server-side (or named) cursors, you must be using PostgresqlExtDatabase.
To execute a query using a server-side cursor, simply wrap your select query using the ServerSide()
helper:
large_query = PageView.select() # Build query normally.
# Iterate over large query inside a transaction.
for page_view in ServerSide(large_query):
# do some interesting analysis here.
pass
# Server-side resources are released.
If you would like all SELECT queries to automatically use a server-side cursor, you can specify this when
creating your PostgresqlExtDatabase:
from postgres_ext import PostgresqlExtDatabase
ss_db = PostgresqlExtDatabase('my_db', server_side_cursors=True)
NOTE:
Server-side cursors live only as long as the transaction, so for this reason peewee will not
automatically call commit() after executing a SELECT query. If you do not commit after you are done
iterating, you will not release the server-side resources until the connection is closed (or the
transaction is committed later). Furthermore, since peewee will by default cache rows returned by the
cursor, you should always call .iterator() when iterating over a large query.
If you are using the ServerSide() helper, the transaction and call to iterator() will be handled
transparently.
Full-text search
Postgresql provides sophisticated full-text search using special data-types (tsvector and tsquery).
Documents should be stored or converted to the tsvector type, and search queries should be converted to
tsquery.
For simple cases, you can simply use the Match() function, which will automatically perform the
appropriate conversions, and requires no schema changes:
def blog_search(query):
return Blog.select().where(
(Blog.status == Blog.STATUS_PUBLISHED) &
Match(Blog.content, query))
The Match() function will automatically convert the left-hand operand to a tsvector, and the right-hand
operand to a tsquery. For better performance, it is recommended you create a GIN index on the column you
plan to search:
CREATE INDEX blog_full_text_search ON blog USING gin(to_tsvector(content));
Alternatively, you can use the TSVectorField to maintain a dedicated column for storing tsvector data:
class Blog(Model):
content = TextField()
search_content = TSVectorField()
You will need to explicitly convert the incoming text data to tsvector when inserting or updating the
search_content field:
content = 'Excellent blog post about peewee ORM.'
blog_entry = Blog.create(
content=content,
search_content=fn.to_tsvector(content))
NOTE:
If you are using the TSVectorField, it will automatically be created with a GIN index.
postgres_ext API notes
class PostgresqlExtDatabase(database[, server_side_cursors=False[, register_hstore=False[, ...]]])
Identical to PostgresqlDatabase but required in order to support:
Parameters
• database (str) -- Name of database to connect to.
• server_side_cursors (bool) -- Whether SELECT queries should utilize server-side cursors.
• register_hstore (bool) -- Register the HStore extension with the connection.
• Server-side cursors
• ArrayField
• DateTimeTZField
• JSONField
• BinaryJSONField
• HStoreField
• TSVectorField
If you wish to use the HStore extension, you must specify register_hstore=True.
If using server_side_cursors, also be sure to wrap your queries with ServerSide().
ServerSide(select_query)
Parameters
select_query -- a SelectQuery instance.
Rtype generator
Wrap the given select query in a transaction, and call it's iterator() method to avoid caching row
instances. In order for the server-side resources to be released, be sure to exhaust the generator
(iterate over all the rows).
Usage:
large_query = PageView.select()
for page_view in ServerSide(large_query):
# Do something interesting.
pass
# At this point server side resources are released.
class ArrayField([field_class=IntegerField[, field_kwargs=None[, dimensions=1[, convert_values=False]]]])
Parameters
• field_class -- a subclass of Field, e.g. IntegerField.
• field_kwargs (dict) -- arguments to initialize field_class.
• dimensions (int) -- dimensions of array.
• convert_values (bool) -- apply field_class value conversion to array data.
Field capable of storing arrays of the provided field_class.
NOTE:
By default ArrayField will use a GIN index. To disable this, initialize the field with
index=False.
You can store and retrieve lists (or lists-of-lists):
class BlogPost(BaseModel):
content = TextField()
tags = ArrayField(CharField)
post = BlogPost(content='awesome', tags=['foo', 'bar', 'baz'])
Additionally, you can use the __getitem__ API to query values or slices in the database:
# Get the first tag on a given blog post.
first_tag = (BlogPost
.select(BlogPost.tags[0].alias('first_tag'))
.where(BlogPost.id == 1)
.dicts()
.get())
# first_tag = {'first_tag': 'foo'}
Get a slice of values:
# Get the first two tags.
two_tags = (BlogPost
.select(BlogPost.tags[:2].alias('two'))
.dicts()
.get())
# two_tags = {'two': ['foo', 'bar']}
contains(*items)
Parameters
items -- One or more items that must be in the given array field.
# Get all blog posts that are tagged with both "python" and "django".
Blog.select().where(Blog.tags.contains('python', 'django'))
contains_any(*items)
Parameters
items -- One or more items to search for in the given array field.
Like contains(), except will match rows where the array contains any of the given items.
# Get all blog posts that are tagged with "flask" and/or "django".
Blog.select().where(Blog.tags.contains_any('flask', 'django'))
class DateTimeTZField(*args, **kwargs)
A timezone-aware subclass of DateTimeField.
class HStoreField(*args, **kwargs)
A field for storing and retrieving arbitrary key/value pairs. For details on usage, see hstore
support.
ATTENTION:
To use the HStoreField you will need to be sure the hstore extension is registered with the
connection. To accomplish this, instantiate the PostgresqlExtDatabase with
register_hstore=True.
NOTE:
By default HStoreField will use a GiST index. To disable this, initialize the field with
index=False.
keys() Returns the keys for a given row.
>>> for h in House.select(House.address, House.features.keys().alias('keys')):
... print(h.address, h.keys)
123 Main St [u'bath', u'garage']
values()
Return the values for a given row.
>>> for h in House.select(House.address, House.features.values().alias('vals')):
... print(h.address, h.vals)
123 Main St [u'2 bath', u'2 cars']
items()
Like python's dict, return the keys and values in a list-of-lists:
>>> for h in House.select(House.address, House.features.items().alias('mtx')):
... print(h.address, h.mtx)
123 Main St [[u'bath', u'2 bath'], [u'garage', u'2 cars']]
slice(*args)
Return a slice of data given a list of keys.
>>> for h in House.select(House.address, House.features.slice('garage').alias('garage_data')):
... print(h.address, h.garage_data)
123 Main St {'garage': '2 cars'}
exists(key)
Query for whether the given key exists.
>>> for h in House.select(House.address, House.features.exists('garage').alias('has_garage')):
... print(h.address, h.has_garage)
123 Main St True
>>> for h in House.select().where(House.features.exists('garage')):
... print(h.address, h.features['garage']) # <-- just houses w/garage data
123 Main St 2 cars
defined(key)
Query for whether the given key has a value associated with it.
update(**data)
Perform an atomic update to the keys/values for a given row or rows.
>>> query = House.update(features=House.features.update(
... sqft=2000,
... year_built=2012))
>>> query.where(House.id == 1).execute()
delete(*keys)
Delete the provided keys for a given row or rows.
NOTE:
We will use an UPDATE query.
>>> query = House.update(features=House.features.delete(
... 'sqft', 'year_built'))
>>> query.where(House.id == 1).execute()
contains(value)
Parameters
value -- Either a dict, a list of keys, or a single key.
Query rows for the existence of either:
• a partial dictionary.
• a list of keys.
• a single key.
>>> query = House.select()
>>> has_garage = query.where(House.features.contains('garage'))
>>> garage_bath = query.where(House.features.contains(['garage', 'bath']))
>>> twocar = query.where(House.features.contains({'garage': '2 cars'}))
contains_any(*keys)
Parameters
keys -- One or more keys to search for.
Query rows for the existence of any key.
class JSONField(dumps=None, *args, **kwargs)
Parameters
dumps -- The default is to call json.dumps() or the dumps function. You can override this
method to create a customized JSON wrapper.
Field class suitable for storing and querying arbitrary JSON. When using this on a model, set the
field's value to a Python object (either a dict or a list). When you retrieve your value from the
database it will be returned as a Python data structure.
NOTE:
You must be using Postgres 9.2 / psycopg2 2.5 or greater.
NOTE:
If you are using Postgres 9.4, strongly consider using the BinaryJSONField instead as it offers
better performance and more powerful querying options.
Example model declaration:
db = PostgresqlExtDatabase('my_db')
class APIResponse(Model):
url = CharField()
response = JSONField()
class Meta:
database = db
Example of storing JSON data:
url = 'http://foo.com/api/resource/'
resp = json.loads(urllib2.urlopen(url).read())
APIResponse.create(url=url, response=resp)
APIResponse.create(url='http://foo.com/baz/', response={'key': 'value'})
To query, use Python's [] operators to specify nested key or array lookups:
APIResponse.select().where(
APIResponse.response['key1']['nested-key'] == 'some-value')
To illustrate the use of the [] operators, imagine we have the following data stored in an
APIResponse:
{
"foo": {
"bar": ["i1", "i2", "i3"],
"baz": {
"huey": "mickey",
"peewee": "nugget"
}
}
}
Here are the results of a few queries:
def get_data(expression):
# Helper function to just retrieve the results of a
# particular expression.
query = (APIResponse
.select(expression.alias('my_data'))
.dicts()
.get())
return query['my_data']
# Accessing the foo -> bar subkey will return a JSON
# representation of the list.
get_data(APIResponse.data['foo']['bar'])
# '["i1", "i2", "i3"]'
# In order to retrieve this list as a Python list,
# we will call .as_json() on the expression.
get_data(APIResponse.data['foo']['bar'].as_json())
# ['i1', 'i2', 'i3']
# Similarly, accessing the foo -> baz subkey will
# return a JSON representation of the dictionary.
get_data(APIResponse.data['foo']['baz'])
# '{"huey": "mickey", "peewee": "nugget"}'
# Again, calling .as_json() will return an actual
# python dictionary.
get_data(APIResponse.data['foo']['baz'].as_json())
# {'huey': 'mickey', 'peewee': 'nugget'}
# When dealing with simple values, either way works as
# you expect.
get_data(APIResponse.data['foo']['bar'][0])
# 'i1'
# Calling .as_json() when the result is a simple value
# will return the same thing as the previous example.
get_data(APIResponse.data['foo']['bar'][0].as_json())
# 'i1'
class BinaryJSONField(dumps=None, *args, **kwargs)
Parameters
dumps -- The default is to call json.dumps() or the dumps function. You can override this
method to create a customized JSON wrapper.
Store and query arbitrary JSON documents. Data should be stored using normal Python dict and list
objects, and when data is returned from the database, it will be returned using dict and list as
well.
For examples of basic query operations, see the above code samples for JSONField. The example
queries below will use the same APIResponse model described above.
NOTE:
By default BinaryJSONField will use a GiST index. To disable this, initialize the field with
index=False.
NOTE:
You must be using Postgres 9.4 / psycopg2 2.5 or newer. If you are using Postgres 9.2 or 9.3,
you can use the regular JSONField instead.
contains(other)
Test whether the given JSON data contains the given JSON fragment or key.
Example:
search_fragment = {
'foo': {'bar': ['i2']}
}
query = (APIResponse
.select()
.where(APIResponse.data.contains(search_fragment)))
# If we're searching for a list, the list items do not need to
# be ordered in a particular way:
query = (APIResponse
.select()
.where(APIResponse.data.contains({
'foo': {'bar': ['i2', 'i1']}})))
We can pass in simple keys as well. To find APIResponses that contain the key foo at the
top-level:
APIResponse.select().where(APIResponse.data.contains('foo'))
We can also search sub-keys using square-brackets:
APIResponse.select().where(
APIResponse.data['foo']['bar'].contains(['i2', 'i1']))
contains_any(*items)
Search for the presence of one or more of the given items.
APIResponse.select().where(
APIResponse.data.contains_any('foo', 'baz', 'nugget'))
Like contains(), we can also search sub-keys:
APIResponse.select().where(
APIResponse.data['foo']['bar'].contains_any('i2', 'ix'))
contains_all(*items)
Search for the presence of all of the given items.
APIResponse.select().where(
APIResponse.data.contains_all('foo'))
Like contains_any(), we can also search sub-keys:
APIResponse.select().where(
APIResponse.data['foo']['bar'].contains_all('i1', 'i2', 'i3'))
contained_by(other)
Test whether the given JSON document is contained by (is a subset of) the given JSON
document. This method is the inverse of contains().
big_doc = {
'foo': {
'bar': ['i1', 'i2', 'i3'],
'baz': {
'huey': 'mickey',
'peewee': 'nugget',
}
},
'other_key': ['nugget', 'bear', 'kitten'],
}
APIResponse.select().where(
APIResponse.data.contained_by(big_doc))
Match(field, query)
Generate a full-text search expression, automatically converting the left-hand operand to a
tsvector, and the right-hand operand to a tsquery.
Example:
def blog_search(query):
return Blog.select().where(
(Blog.status == Blog.STATUS_PUBLISHED) &
Match(Blog.content, query))
class TSVectorField
Field type suitable for storing tsvector data. This field will automatically be created with a GIN
index for improved search performance.
NOTE:
Data stored in this field will still need to be manually converted to the tsvector type.
NOTE:
By default TSVectorField will use a GIN index. To disable this, initialize the field with
index=False.
Example usage:
class Blog(Model):
content = TextField()
search_content = TSVectorField()
content = 'this is a sample blog entry.'
blog_entry = Blog.create(
content=content,
search_content=fn.to_tsvector(content)) # Note `to_tsvector()`.
MySQL Extensions
Peewee provides an alternate database implementation for using the mysql-connector driver. The
implementation can be found in playhouse.mysql_ext.
Example usage:
from playhouse.mysql_ext import MySQLConnectorDatabase
# MySQL database implementation that utilizes mysql-connector driver.
db = MySQLConnectorDatabase('my_database', host='1.2.3.4', user='mysql')
DataSet
The dataset module contains a high-level API for working with databases modeled after the popular project
of the same name. The aims of the dataset module are to provide:
• A simplified API for working with relational data, along the lines of working with JSON.
• An easy way to export relational data as JSON or CSV.
• An easy way to import JSON or CSV data into a relational database.
A minimal data-loading script might look like this:
from playhouse.dataset import DataSet
db = DataSet('sqlite:///:memory:')
table = db['sometable']
table.insert(name='Huey', age=3)
table.insert(name='Mickey', age=5, gender='male')
huey = table.find_one(name='Huey')
print huey
# {'age': 3, 'gender': None, 'id': 1, 'name': 'Huey'}
for obj in table:
print obj
# {'age': 3, 'gender': None, 'id': 1, 'name': 'Huey'}
# {'age': 5, 'gender': 'male', 'id': 2, 'name': 'Mickey'}
You can export or import data using freeze() and thaw():
# Export table content to the `users.json` file.
db.freeze(table.all(), format='json', filename='users.json')
# Import data from a CSV file into a new table. Columns will be automatically
# created for each field in the CSV file.
new_table = db['stats']
new_table.thaw(format='csv', filename='monthly_stats.csv')
Getting started
DataSet objects are initialized by passing in a database URL of the format
dialect://user:password@host/dbname. See the Database URL section for examples of connecting to various
databases.
# Create an in-memory SQLite database.
db = DataSet('sqlite:///:memory:')
Storing data
To store data, we must first obtain a reference to a table. If the table does not exist, it will be
created automatically:
# Get a table reference, creating the table if it does not exist.
table = db['users']
We can now insert() new rows into the table. If the columns do not exist, they will be created
automatically:
table.insert(name='Huey', age=3, color='white')
table.insert(name='Mickey', age=5, gender='male')
To update existing entries in the table, pass in a dictionary containing the new values and filter
conditions. The list of columns to use as filters is specified in the columns argument. If no filter
columns are specified, then all rows will be updated.
# Update the gender for "Huey".
table.update(name='Huey', gender='male', columns=['name'])
# Update all records. If the column does not exist, it will be created.
table.update(favorite_orm='peewee')
Importing data
To import data from an external source, such as a JSON or CSV file, you can use the thaw() method. By
default, new columns will be created for any attributes encountered. If you wish to only populate columns
that are already defined on a table, you can pass in strict=True.
# Load data from a JSON file containing a list of objects.
table = dataset['stock_prices']
table.thaw(filename='stocks.json', format='json')
table.all()[:3]
# Might print...
[{'id': 1, 'ticker': 'GOOG', 'price': 703},
{'id': 2, 'ticker': 'AAPL', 'price': 109},
{'id': 3, 'ticker': 'AMZN', 'price': 300}]
Using transactions
DataSet supports nesting transactions using a simple context manager.
table = db['users']
with db.transaction() as txn:
table.insert(name='Charlie')
with db.transaction() as nested_txn:
# Set Charlie's favorite ORM to Django.
table.update(name='Charlie', favorite_orm='django', columns=['name'])
# jk/lol
nested_txn.rollback()
Inspecting the database
You can use the tables() method to list the tables in the current database:
>>> print db.tables
['sometable', 'user']
And for a given table, you can print the columns:
>>> table = db['user']
>>> print table.columns
['id', 'age', 'name', 'gender', 'favorite_orm']
We can also find out how many rows are in a table:
>>> print len(db['user'])
3
Reading data
To retrieve all rows, you can use the all() method:
# Retrieve all the users.
users = db['user'].all()
# We can iterate over all rows without calling `.all()`
for user in db['user']:
print user['name']
Specific objects can be retrieved using find() and find_one().
# Find all the users who like peewee.
peewee_users = db['user'].find(favorite_orm='peewee')
# Find Huey.
huey = db['user'].find_one(name='Huey')
Exporting data
To export data, use the freeze() method, passing in the query you wish to export:
peewee_users = db['user'].find(favorite_orm='peewee')
db.freeze(peewee_users, format='json', filename='peewee_users.json')
API
class DataSet(url)
Parameters
url -- A database URL or a Database instance. For details on using a URL, see Database URL
for examples.
The DataSet class provides a high-level API for working with relational databases.
tables Return a list of tables stored in the database. This list is computed dynamically each time
it is accessed.
__getitem__(table_name)
Provide a Table reference to the specified table. If the table does not exist, it will be
created.
query(sql[, params=None[, commit=True]])
Parameters
• sql (str) -- A SQL query.
• params (list) -- Optional parameters for the query.
• commit (bool) -- Whether the query should be committed upon execution.
Returns
A database cursor.
Execute the provided query against the database.
transaction()
Create a context manager representing a new transaction (or savepoint).
freeze(query[, format='csv'[, filename=None[, file_obj=None[, **kwargs]]]])
Parameters
• query -- A SelectQuery, generated using all() or ~Table.find.
• format -- Output format. By default, csv and json are supported.
• filename -- Filename to write output to.
• file_obj -- File-like object to write output to.
• kwargs -- Arbitrary parameters for export-specific functionality.
thaw(table[, format='csv'[, filename=None[, file_obj=None[, strict=False[, **kwargs]]]]])
Parameters
• table (str) -- The name of the table to load data into.
• format -- Input format. By default, csv and json are supported.
• filename -- Filename to read data from.
• file_obj -- File-like object to read data from.
• strict (bool) -- Whether to store values for columns that do not already exist on
the table.
• kwargs -- Arbitrary parameters for import-specific functionality.
connect()
Open a connection to the underlying database. If a connection is not opened explicitly, one
will be opened the first time a query is executed.
close()
Close the connection to the underlying database.
class Table(dataset, name, model_class)
Provides a high-level API for working with rows in a given table.
columns
Return a list of columns in the given table.
model_class
A dynamically-created Model class.
create_index(columns[, unique=False])
Create an index on the given columns:
# Create a unique index on the `username` column.
db['users'].create_index(['username'], unique=True)
insert(**data)
Insert the given data dictionary into the table, creating new columns as needed.
update(columns=None, conjunction=None, **data)
Update the table using the provided data. If one or more columns are specified in the
columns parameter, then those columns' values in the data dictionary will be used to
determine which rows to update.
# Update all rows.
db['users'].update(favorite_orm='peewee')
# Only update Huey's record, setting his age to 3.
db['users'].update(name='Huey', age=3, columns=['name'])
find(**query)
Query the table for rows matching the specified equality conditions. If no query is
specified, then all rows are returned.
peewee_users = db['users'].find(favorite_orm='peewee')
find_one(**query)
Return a single row matching the specified equality conditions. If no matching row is found
then None will be returned.
huey = db['users'].find_one(name='Huey')
all() Return all rows in the given table.
delete(**query)
Delete all rows matching the given equality conditions. If no query is provided, then all
rows will be deleted.
# Adios, Django!
db['users'].delete(favorite_orm='Django')
# Delete all the secret messages.
db['secret_messages'].delete()
freeze([format='csv'[, filename=None[, file_obj=None[, **kwargs]]]])
Parameters
• format -- Output format. By default, csv and json are supported.
• filename -- Filename to write output to.
• file_obj -- File-like object to write output to.
• kwargs -- Arbitrary parameters for export-specific functionality.
thaw([format='csv'[, filename=None[, file_obj=None[, strict=False[, **kwargs]]]]])
Parameters
• format -- Input format. By default, csv and json are supported.
• filename -- Filename to read data from.
• file_obj -- File-like object to read data from.
• strict (bool) -- Whether to store values for columns that do not already exist on
the table.
• kwargs -- Arbitrary parameters for import-specific functionality.
Fields
These fields can be found in the playhouse.fields module.
class CompressedField([compression_level=6[, algorithm='zlib'[, **kwargs]]])
Parameters
• compression_level (int) -- A value from 0 to 9.
• algorithm (str) -- Either 'zlib' or 'bz2'.
Stores compressed data using the specified algorithm. This field extends BlobField, transparently
storing a compressed representation of the data in the database.
class PickleField
Stores arbitrary Python data by transparently pickling and un-pickling data stored in the field.
This field extends BlobField. If the cPickle module is available, it will be used.
Hybrid Attributes
Hybrid attributes encapsulate functionality that operates at both the Python and SQL levels. The idea for
hybrid attributes comes from a feature of the same name in SQLAlchemy. Consider the following example:
class Interval(Model):
start = IntegerField()
end = IntegerField()
@hybrid_property
def length(self):
return self.end - self.start
@hybrid_method
def contains(self, point):
return (self.start <= point) & (point < self.end)
The hybrid attribute gets its name from the fact that the length attribute will behave differently
depending on whether it is accessed via the Interval class or an Interval instance.
If accessed via an instance, then it behaves just as you would expect.
If accessed via the Interval.length class attribute, however, the length calculation will be expressed as
a SQL expression. For example:
query = Interval.select().where(Interval.length > 5)
This query will be equivalent to the following SQL:
SELECT "t1"."id", "t1"."start", "t1"."end"
FROM "interval" AS t1
WHERE (("t1"."end" - "t1"."start") > 5)
The playhouse.hybrid module also contains a decorator for implementing hybrid methods which can accept
parameters. As with hybrid properties, when accessed via a model instance, then the function executes
normally as-written. When the hybrid method is called on the class, however, it will generate a SQL
expression.
Example:
query = Interval.select().where(Interval.contains(2))
This query is equivalent to the following SQL:
SELECT "t1"."id", "t1"."start", "t1"."end"
FROM "interval" AS t1
WHERE (("t1"."start" <= 2) AND (2 < "t1"."end"))
There is an additional API for situations where the python implementation differs slightly from the SQL
implementation. Let's add a radius method to the Interval model. Because this method calculates an
absolute value, we will use the Python abs() function for the instance portion and the fn.ABS() SQL
function for the class portion.
class Interval(Model):
start = IntegerField()
end = IntegerField()
@hybrid_property
def length(self):
return self.end - self.start
@hybrid_property
def radius(self):
return abs(self.length) / 2
@radius.expression
def radius(cls):
return fn.ABS(cls.length) / 2
What is neat is that both the radius implementations refer to the length hybrid attribute! When accessed
via an Interval instance, the radius calculation will be executed in Python. When invoked via an Interval
class, we will get the appropriate SQL.
Example:
query = Interval.select().where(Interval.radius < 3)
This query is equivalent to the following SQL:
SELECT "t1"."id", "t1"."start", "t1"."end"
FROM "interval" AS t1
WHERE ((abs("t1"."end" - "t1"."start") / 2) < 3)
Pretty neat, right? Thanks for the cool idea, SQLAlchemy!
Hybrid API
class hybrid_method(func[, expr=None])
Method decorator that allows the definition of a Python object method with both instance-level and
class-level behavior.
Example:
class Interval(Model):
start = IntegerField()
end = IntegerField()
@hybrid_method
def contains(self, point):
return (self.start <= point) & (point < self.end)
When called with an Interval instance, the contains method will behave as you would expect. When
called as a classmethod, though, a SQL expression will be generated:
query = Interval.select().where(Interval.contains(2))
Would generate the following SQL:
SELECT "t1"."id", "t1"."start", "t1"."end"
FROM "interval" AS t1
WHERE (("t1"."start" <= 2) AND (2 < "t1"."end"))
expression(expr)
Method decorator for specifying the SQL-expression producing method.
class hybrid_property(fget[, fset=None[, fdel=None[, expr=None]]])
Method decorator that allows the definition of a Python object property with both instance-level
and class-level behavior.
Examples:
class Interval(Model):
start = IntegerField()
end = IntegerField()
@hybrid_property
def length(self):
return self.end - self.start
@hybrid_property
def radius(self):
return abs(self.length) / 2
@radius.expression
def radius(cls):
return fn.ABS(cls.length) / 2
When accessed on an Interval instance, the length and radius properties will behave as you would
expect. When accessed as class attributes, though, a SQL expression will be generated instead:
query = (Interval
.select()
.where(
(Interval.length > 6) &
(Interval.radius >= 3)))
Would generate the following SQL:
SELECT "t1"."id", "t1"."start", "t1"."end"
FROM "interval" AS t1
WHERE (
(("t1"."end" - "t1"."start") > 6) AND
((abs("t1"."end" - "t1"."start") / 2) >= 3)
)
Key/Value Store
The playhouse.kv module contains the implementation of a persistent dictionary.
class KeyValue([key_field=None[, value_field=None[, ordered=False[, database=None[,
table_name='keyvalue']]]]])
Parameters
• key_field (Field) -- field to use for key. Defaults to CharField. Must have
primary_key=True.
• value_field (Field) -- field to use for value. Defaults to PickleField.
• ordered (bool) -- data should be returned in key-sorted order.
• database (Database) -- database where key/value data is stored. If not specified, an
in-memory SQLite database will be used.
• table_name (str) -- table name for data storage.
Dictionary-like API for storing key/value data. Like dictionaries, supports the expected APIs, but
also has the added capability of accepting expressions for getting, setting and deleting items.
Table is created automatically (if it doesn't exist) when the KeyValue is instantiated.
Basic examples:
# Create a key/value store, which uses an in-memory SQLite database
# for data storage.
KV = KeyValue()
# Set (or overwrite) the value for "k1".
KV['k1'] = 'v1'
# Set (or update) multiple keys at once.
KV.update(k2='v2', k3='v3')
# Getting values works as you'd expect.
assert KV['k2'] == 'v2'
# We can also do this:
for value in KV[KV.key > 'k1']:
print(value)
# 'v2'
# 'v3'
# Update multiple values at once using expression:
KV[KV.key > 'k1'] = 'vx'
# What's stored in the KV?
print(dict(KV))
# {'k1': 'v1', 'k2': 'vx', 'k3': 'vx'}
# Delete a single item.
del KV['k2']
# How many items are stored in the KV?
print(len(KV))
# 2
# Delete items that match the given condition.
del KV[KV.key > 'k1']
__contains__(expr)
Parameters
expr -- a single key or an expression
Returns
Boolean whether key/expression exists.
Example:
>>> kv = KeyValue()
>>> kv.update(k1='v1', k2='v2')
>>> 'k1' in kv
True
>>> 'kx' in kv
False
>>> (KV.key < 'k2') in KV
True
>>> (KV.key > 'k2') in KV
False
__len__()
Returns
Count of items stored.
__getitem__(expr)
Parameters
expr -- a single key or an expression.
Returns
value(s) corresponding to key/expression.
Raises KeyError if single key given and not found.
Examples:
>>> KV = KeyValue()
>>> KV.update(k1='v1', k2='v2', k3='v3')
>>> KV['k1']
'v1'
>>> KV['kx']
KeyError: "kx" not found
>>> KV[KV.key > 'k1']
['v2', 'v3']
>>> KV[KV.key < 'k1']
[]
__setitem__(expr, value)
Parameters
• expr -- a single key or an expression.
• value -- value to set for key(s)
Set value for the given key. If expr is an expression, then any keys matching the
expression will have their value updated.
Example:
>>> KV = KeyValue()
>>> KV.update(k1='v1', k2='v2', k3='v3')
>>> KV['k1'] = 'v1-x'
>>> print(KV['k1'])
'v1-x'
>>> KV[KV.key >= 'k2'] = 'v99'
>>> dict(KV)
{'k1': 'v1-x', 'k2': 'v99', 'k3': 'v99'}
__delitem__(expr)
Parameters
expr -- a single key or an expression.
Delete the given key. If an expression is given, delete all keys that match the expression.
Example:
>>> KV = KeyValue()
>>> KV.update(k1=1, k2=2, k3=3)
>>> del KV['k1'] # Deletes "k1".
>>> del KV['k1']
KeyError: "k1" does not exist
>>> del KV[KV.key > 'k2'] # Deletes "k3".
>>> del KV[KV.key > 'k99'] # Nothing deleted, no keys match.
keys()
Returns
an iterable of all keys in the table.
values()
Returns
an iterable of all values in the table.
items()
Returns
an iterable of all key/value pairs in the table.
update([__data=None[, **mapping]])
Efficiently bulk-insert or replace the given key/value pairs.
Example:
>>> KV = KeyValue()
>>> KV.update(k1=1, k2=2) # Sets 'k1'=1, 'k2'=2.
>>> dict(KV)
{'k1': 1, 'k2': 2}
>>> KV.update(k2=22, k3=3) # Updates 'k2'->22, sets 'k3'=3.
>>> dict(KV)
{'k1': 1, 'k2': 22, 'k3': 3}
>>> KV.update({'k2': -2, 'k4': 4}) # Also can pass a dictionary.
>>> dict(KV)
{'k1': 1, 'k2': -2, 'k3': 3, 'k4': 4}
ATTENTION:
Because Postgresql does not support INSERT + REPLACE, the KeyValue.update() method is
not supported for Postgresql databases (as it cannot be implemented efficiently).
get(expr[, default=None])
Parameters
• expr -- a single key or an expression.
• default -- default value if key not found.
Returns
value of given key/expr or default if single key not found.
Get the value at the given key. If the key does not exist, the default value is returned,
unless the key is an expression in which case an empty list will be returned.
pop(expr[, default=Sentinel])
Parameters
• expr -- a single key or an expression.
• default -- default value if key does not exist.
Returns
value of given key/expr or default if single key not found.
Get value and delete the given key. If the key does not exist, the default value is
returned, unless the key is an expression in which case an empty list is returned.
clear()
Remove all items from the key-value table.
Shortcuts
This module contains helper functions for expressing things that would otherwise be somewhat verbose or
cumbersome using peewee's APIs. There are also helpers for serializing models to dictionaries and
vice-versa.
model_to_dict(model[, recurse=True[, backrefs=False[, only=None[, exclude=None[, extra_attrs=None[,
fields_from_query=None[, max_depth=None[, manytomany=False]]]]]]]])
Parameters
• recurse (bool) -- Whether foreign-keys should be recursed.
• backrefs (bool) -- Whether lists of related objects should be recursed.
• only -- A list (or set) of field instances which should be included in the result
dictionary.
• exclude -- A list (or set) of field instances which should be excluded from the result
dictionary.
• extra_attrs -- A list of attribute or method names on the instance which should be
included in the dictionary.
• fields_from_query (Select) -- The SelectQuery that created this model instance. Only the
fields and values explicitly selected by the query will be serialized.
• max_depth (int) -- Maximum depth when recursing.
• manytomany (bool) -- Process many-to-many fields.
Convert a model instance (and optionally any related instances) to a dictionary.
Examples:
>>> user = User.create(username='charlie')
>>> model_to_dict(user)
{'id': 1, 'username': 'charlie'}
>>> model_to_dict(user, backrefs=True)
{'id': 1, 'tweets': [], 'username': 'charlie'}
>>> t1 = Tweet.create(user=user, message='tweet-1')
>>> t2 = Tweet.create(user=user, message='tweet-2')
>>> model_to_dict(user, backrefs=True)
{
'id': 1,
'tweets': [
{'id': 1, 'message': 'tweet-1'},
{'id': 2, 'message': 'tweet-2'},
],
'username': 'charlie'
}
>>> model_to_dict(t1)
{
'id': 1,
'message': 'tweet-1',
'user': {
'id': 1,
'username': 'charlie'
}
}
>>> model_to_dict(t2, recurse=False)
{'id': 1, 'message': 'tweet-2', 'user': 1}
dict_to_model(model_class, data[, ignore_unknown=False])
Parameters
• model_class (Model) -- The model class to construct.
• data (dict) -- A dictionary of data. Foreign keys can be included as nested dictionaries,
and back-references as lists of dictionaries.
• ignore_unknown (bool) -- Whether to allow unrecognized (non-field) attributes.
Convert a dictionary of data to a model instance, creating related instances where appropriate.
Examples:
>>> user_data = {'id': 1, 'username': 'charlie'}
>>> user = dict_to_model(User, user_data)
>>> user
<__main__.User at 0x7fea8fa4d490>
>>> user.username
'charlie'
>>> note_data = {'id': 2, 'text': 'note text', 'user': user_data}
>>> note = dict_to_model(Note, note_data)
>>> note.text
'note text'
>>> note.user.username
'charlie'
>>> user_with_notes = {
... 'id': 1,
... 'username': 'charlie',
... 'notes': [{'id': 1, 'text': 'note-1'}, {'id': 2, 'text': 'note-2'}]}
>>> user = dict_to_model(User, user_with_notes)
>>> user.notes[0].text
'note-1'
>>> user.notes[0].user.username
'charlie'
update_model_from_dict(instance, data[, ignore_unknown=False])
Parameters
• instance (Model) -- The model instance to update.
• data (dict) -- A dictionary of data. Foreign keys can be included as nested dictionaries,
and back-references as lists of dictionaries.
• ignore_unknown (bool) -- Whether to allow unrecognized (non-field) attributes.
Update a model instance with the given data dictionary.
Signal support
Models with hooks for signals (a-la django) are provided in playhouse.signals. To use the signals, you
will need all of your project's models to be a subclass of playhouse.signals.Model, which overrides the
necessary methods to provide support for the various signals.
from playhouse.signals import Model, post_save
class MyModel(Model):
data = IntegerField()
@post_save(sender=MyModel)
def on_save_handler(model_class, instance, created):
put_data_in_cache(instance.data)
WARNING:
For what I hope are obvious reasons, Peewee signals do not work when you use the Model.insert(),
Model.update(), or Model.delete() methods. These methods generate queries that execute beyond the
scope of the ORM, and the ORM does not know about which model instances might or might not be affected
when the query executes.
Signals work by hooking into the higher-level peewee APIs like Model.save() and
Model.delete_instance(), where the affected model instance is known ahead of time.
The following signals are provided:
pre_save
Called immediately before an object is saved to the database. Provides an additional keyword
argument created, indicating whether the model is being saved for the first time or updated.
post_save
Called immediately after an object is saved to the database. Provides an additional keyword
argument created, indicating whether the model is being saved for the first time or updated.
pre_delete
Called immediately before an object is deleted from the database when Model.delete_instance() is
used.
post_delete
Called immediately after an object is deleted from the database when Model.delete_instance() is
used.
pre_init
Called when a model class is first instantiated
Connecting handlers
Whenever a signal is dispatched, it will call any handlers that have been registered. This allows totally
separate code to respond to events like model save and delete.
The Signal class provides a connect() method, which takes a callback function and two optional parameters
for "sender" and "name". If specified, the "sender" parameter should be a single model class and allows
your callback to only receive signals from that one model class. The "name" parameter is used as a
convenient alias in the event you wish to unregister your signal handler.
Example usage:
from playhouse.signals import *
def post_save_handler(sender, instance, created):
print '%s was just saved' % instance
# our handler will only be called when we save instances of SomeModel
post_save.connect(post_save_handler, sender=SomeModel)
All signal handlers accept as their first two arguments sender and instance, where sender is the model
class and instance is the actual model being acted upon.
If you'd like, you can also use a decorator to connect signal handlers. This is functionally equivalent
to the above example:
@post_save(sender=SomeModel)
def post_save_handler(sender, instance, created):
print '%s was just saved' % instance
Signal API
class Signal
Stores a list of receivers (callbacks) and calls them when the "send" method is invoked.
connect(receiver[, sender=None[, name=None]])
Parameters
• receiver (callable) -- a callable that takes at least two parameters, a "sender",
which is the Model subclass that triggered the signal, and an "instance", which is
the actual model instance.
• sender (Model) -- if specified, only instances of this model class will trigger
the receiver callback.
• name (string) -- a short alias
Add the receiver to the internal list of receivers, which will be called whenever the
signal is sent.
from playhouse.signals import post_save
from project.handlers import cache_buster
post_save.connect(cache_buster, name='project.cache_buster')
disconnect([receiver=None[, name=None]])
Parameters
• receiver (callable) -- the callback to disconnect
• name (string) -- a short alias
Disconnect the given receiver (or the receiver with the given name alias) so that it no
longer is called. Either the receiver or the name must be provided.
post_save.disconnect(name='project.cache_buster')
send(instance, *args, **kwargs)
Parameters
instance -- a model instance
Iterates over the receivers and will call them in the order in which they were connected.
If the receiver specified a sender, it will only be called if the instance is an instance
of the sender.
pwiz, a model generator
pwiz is a little script that ships with peewee and is capable of introspecting an existing database and
generating model code suitable for interacting with the underlying data. If you have a database already,
pwiz can give you a nice boost by generating skeleton code with correct column affinities and foreign
keys.
If you install peewee using setup.py install, pwiz will be installed as a "script" and you can just run:
python -m pwiz -e postgresql -u postgres my_postgres_db
This will print a bunch of models to standard output. So you can do this:
python -m pwiz -e postgresql my_postgres_db > mymodels.py
python # <-- fire up an interactive shell
>>> from mymodels import Blog, Entry, Tag, Whatever
>>> print [blog.name for blog in Blog.select()]
Command-line options
pwiz accepts the following command-line options:
┌───────┬──────────────────────────────┬──────────────────────────────┐
│Option │ Meaning │ Example │
├───────┼──────────────────────────────┼──────────────────────────────┤
│-h │ show help │ │
├───────┼──────────────────────────────┼──────────────────────────────┤
│-e │ database backend │ -e mysql │
├───────┼──────────────────────────────┼──────────────────────────────┤
│-H │ host to connect to │ -H remote.db.server │
├───────┼──────────────────────────────┼──────────────────────────────┤
│-p │ port to connect on │ -p 9001 │
├───────┼──────────────────────────────┼──────────────────────────────┤
│-u │ database user │ -u postgres │
├───────┼──────────────────────────────┼──────────────────────────────┤
│-P │ database password │ -P (will be prompted for │
│ │ │ password) │
├───────┼──────────────────────────────┼──────────────────────────────┤
│-s │ schema │ -s public │
├───────┼──────────────────────────────┼──────────────────────────────┤
│-t │ tables to generate │ -t tweet,users,relationships │
├───────┼──────────────────────────────┼──────────────────────────────┤
│-v │ generate models for VIEWs │ (no argument) │
├───────┼──────────────────────────────┼──────────────────────────────┤
│-i │ add info metadata to │ (no argument) │
│ │ generated file │ │
└───────┴──────────────────────────────┴──────────────────────────────┘
│-o │ table column order is │ (no argument) │
│ │ preserved │ │
└───────┴──────────────────────────────┴──────────────────────────────┘
The following are valid parameters for the engine (-e):
• sqlite
• mysql
• postgresql
WARNING:
If a password is required to access your database, you will be prompted to enter it using a secure
prompt.
The password will be included in the output. Specifically, at the top of the file a Database will be
defined along with any required parameters -- including the password.
pwiz examples
Examples of introspecting various databases:
# Introspect a Sqlite database.
python -m pwiz -e sqlite path/to/sqlite_database.db
# Introspect a MySQL database, logging in as root. You will be prompted
# for a password ("-P").
python -m pwiz -e mysql -u root -P mysql_db_name
# Introspect a Postgresql database on a remote server.
python -m pwiz -e postgres -u postgres -H 10.1.0.3 pg_db_name
Full example:
$ sqlite3 example.db << EOM
CREATE TABLE "user" ("id" INTEGER NOT NULL PRIMARY KEY, "username" TEXT NOT NULL);
CREATE TABLE "tweet" (
"id" INTEGER NOT NULL PRIMARY KEY,
"content" TEXT NOT NULL,
"timestamp" DATETIME NOT NULL,
"user_id" INTEGER NOT NULL,
FOREIGN KEY ("user_id") REFERENCES "user" ("id"));
CREATE UNIQUE INDEX "user_username" ON "user" ("username");
EOM
$ python -m pwiz -e sqlite example.db
Produces the following output:
from peewee import *
database = SqliteDatabase('example.db', **{})
class UnknownField(object):
def __init__(self, *_, **__): pass
class BaseModel(Model):
class Meta:
database = database
class User(BaseModel):
username = TextField(unique=True)
class Meta:
table_name = 'user'
class Tweet(BaseModel):
content = TextField()
timestamp = DateTimeField()
user = ForeignKeyField(column_name='user_id', field='id', model=User)
class Meta:
table_name = 'tweet'
Observations:
• The foreign-key Tweet.user_id is detected and mapped correctly.
• The User.username UNIQUE constraint is detected.
• Each model explicitly declares its table name, even in cases where it is not necessary (as Peewee would
automatically translate the class name into the appropriate table name).
• All the parameters of the ForeignKeyField are explicitly declared, even though they follow the
conventions Peewee uses by default.
NOTE:
The UnknownField is a placeholder that is used in the event your schema contains a column declaration
that Peewee doesn't know how to map to a field class.
Schema Migrations
Peewee now supports schema migrations, with well-tested support for Postgresql, SQLite and MySQL. Unlike
other schema migration tools, peewee's migrations do not handle introspection and database "versioning".
Rather, peewee provides a number of helper functions for generating and running schema-altering
statements. This engine provides the basis on which a more sophisticated tool could some day be built.
Migrations can be written as simple python scripts and executed from the command-line. Since the
migrations only depend on your applications Database object, it should be easy to manage changing your
model definitions and maintaining a set of migration scripts without introducing dependencies.
Example usage
Begin by importing the helpers from the migrate module:
from playhouse.migrate import *
Instantiate a migrator. The SchemaMigrator class is responsible for generating schema altering
operations, which can then be run sequentially by the migrate() helper.
# Postgres example:
my_db = PostgresqlDatabase(...)
migrator = PostgresqlMigrator(my_db)
# SQLite example:
my_db = SqliteDatabase('my_database.db')
migrator = SqliteMigrator(my_db)
Use migrate() to execute one or more operations:
title_field = CharField(default='')
status_field = IntegerField(null=True)
migrate(
migrator.add_column('some_table', 'title', title_field),
migrator.add_column('some_table', 'status', status_field),
migrator.drop_column('some_table', 'old_column'),
)
WARNING:
Migrations are not run inside a transaction. If you wish the migration to run in a transaction you
will need to wrap the call to migrate in a atomic() context-manager, e.g.
with my_db.atomic():
migrate(...)
Supported Operations
Add new field(s) to an existing model:
# Create your field instances. For non-null fields you must specify a
# default value.
pubdate_field = DateTimeField(null=True)
comment_field = TextField(default='')
# Run the migration, specifying the database table, field name and field.
migrate(
migrator.add_column('comment_tbl', 'pub_date', pubdate_field),
migrator.add_column('comment_tbl', 'comment', comment_field),
)
Renaming a field:
# Specify the table, original name of the column, and its new name.
migrate(
migrator.rename_column('story', 'pub_date', 'publish_date'),
migrator.rename_column('story', 'mod_date', 'modified_date'),
)
Dropping a field:
migrate(
migrator.drop_column('story', 'some_old_field'),
)
Making a field nullable or not nullable:
# Note that when making a field not null that field must not have any
# NULL values present.
migrate(
# Make `pub_date` allow NULL values.
migrator.drop_not_null('story', 'pub_date'),
# Prevent `modified_date` from containing NULL values.
migrator.add_not_null('story', 'modified_date'),
)
Renaming a table:
migrate(
migrator.rename_table('story', 'stories_tbl'),
)
Adding an index:
# Specify the table, column names, and whether the index should be
# UNIQUE or not.
migrate(
# Create an index on the `pub_date` column.
migrator.add_index('story', ('pub_date',), False),
# Create a multi-column index on the `pub_date` and `status` fields.
migrator.add_index('story', ('pub_date', 'status'), False),
# Create a unique index on the category and title fields.
migrator.add_index('story', ('category_id', 'title'), True),
)
Dropping an index:
# Specify the index name.
migrate(migrator.drop_index('story', 'story_pub_date_status'))
Adding or dropping table constraints:
# Add a CHECK() constraint to enforce the price cannot be negative.
migrate(migrator.add_constraint(
'products',
'price_check',
Check('price >= 0')))
# Remove the price check constraint.
migrate(migrator.drop_constraint('products', 'price_check'))
# Add a UNIQUE constraint on the first and last names.
migrate(migrator.add_unique('person', 'first_name', 'last_name'))
Migrations API
migrate(*operations)
Execute one or more schema altering operations.
Usage:
migrate(
migrator.add_column('some_table', 'new_column', CharField(default='')),
migrator.create_index('some_table', ('new_column',)),
)
class SchemaMigrator(database)
Parameters
database -- a Database instance.
The SchemaMigrator is responsible for generating schema-altering statements.
add_column(table, column_name, field)
Parameters
• table (str) -- Name of the table to add column to.
• column_name (str) -- Name of the new column.
• field (Field) -- A Field instance.
Add a new column to the provided table. The field provided will be used to generate the
appropriate column definition.
NOTE:
If the field is not nullable it must specify a default value.
NOTE:
For non-null fields, the field will initially be added as a null field, then an UPDATE
statement will be executed to populate the column with the default value. Finally, the
column will be marked as not null.
drop_column(table, column_name[, cascade=True])
Parameters
• table (str) -- Name of the table to drop column from.
• column_name (str) -- Name of the column to drop.
• cascade (bool) -- Whether the column should be dropped with CASCADE.
rename_column(table, old_name, new_name)
Parameters
• table (str) -- Name of the table containing column to rename.
• old_name (str) -- Current name of the column.
• new_name (str) -- New name for the column.
add_not_null(table, column)
Parameters
• table (str) -- Name of table containing column.
• column (str) -- Name of the column to make not nullable.
drop_not_null(table, column)
Parameters
• table (str) -- Name of table containing column.
• column (str) -- Name of the column to make nullable.
rename_table(old_name, new_name)
Parameters
• old_name (str) -- Current name of the table.
• new_name (str) -- New name for the table.
add_index(table, columns[, unique=False[, using=None]])
Parameters
• table (str) -- Name of table on which to create the index.
• columns (list) -- List of columns which should be indexed.
• unique (bool) -- Whether the new index should specify a unique constraint.
• using (str) -- Index type (where supported), e.g. GiST or GIN.
drop_index(table, index_name)
Parameters
• table (str) -- Name of the table containing the index to be dropped.
• index_name (str) -- Name of the index to be dropped.
add_constraint(table, name, constraint)
Parameters
• table (str) -- Table to add constraint to.
• name (str) -- Name used to identify the constraint.
• constraint -- either a Check() constraint or for adding an arbitrary constraint
use SQL.
drop_constraint(table, name)
Parameters
• table (str) -- Table to drop constraint from.
• name (str) -- Name of constraint to drop.
add_unique(table, *column_names)
Parameters
• table (str) -- Table to add constraint to.
• column_names (str) -- One or more columns for UNIQUE constraint.
class PostgresqlMigrator(database)
Generate migrations for Postgresql databases.
set_search_path(schema_name)
Parameters
schema_name (str) -- Schema to use.
Set the search path (schema) for the subsequent operations.
class SqliteMigrator(database)
Generate migrations for SQLite databases.
SQLite has limited support for ALTER TABLE queries, so the following operations are currently not
supported for SQLite:
• add_constraint
• drop_constraint
• add_unique
class MySQLMigrator(database)
Generate migrations for MySQL databases.
Reflection
The reflection module contains helpers for introspecting existing databases. This module is used
internally by several other modules in the playhouse, including DataSet and pwiz, a model generator.
class Introspector(metadata[, schema=None])
Metadata can be extracted from a database by instantiating an Introspector. Rather than
instantiating this class directly, it is recommended to use the factory method from_database().
classmethod from_database(database[, schema=None])
Parameters
• database -- a Database instance.
• schema (str) -- an optional schema (supported by some databases).
Creates an Introspector instance suitable for use with the given database.
Usage:
db = SqliteDatabase('my_app.db')
introspector = Introspector.from_database(db)
models = introspector.generate_models()
# User and Tweet (assumed to exist in the database) are
# peewee Model classes generated from the database schema.
User = models['user']
Tweet = models['tweet']
generate_models([skip_invalid=False[, table_names=None[, literal_column_names=False[,
bare_fields=False[, include_views=False]]]]])
Parameters
• skip_invalid (bool) -- Skip tables whose names are invalid python identifiers.
• table_names (list) -- List of table names to generate. If unspecified, models are
generated for all tables.
• literal_column_names (bool) -- Use column-names as-is. By default, column names
are "python-ized", i.e. mixed-case becomes lower-case.
• bare_fields -- SQLite-only. Do not specify data-types for introspected columns.
• include_views -- generate models for VIEWs as well.
Returns
A dictionary mapping table-names to model classes.
Introspect the database, reading in the tables, columns, and foreign key constraints, then
generate a dictionary mapping each database table to a dynamically-generated Model class.
Database URL
This module contains a helper function to generate a database connection from a URL connection string.
connect(url, **connect_params)
Create a Database instance from the given connection URL.
Examples:
• sqlite:///my_database.db will create a SqliteDatabase instance for the file my_database.db in
the current directory.
• sqlite:///:memory: will create an in-memory SqliteDatabase instance.
• postgresql://postgres:my_password@localhost:5432/my_database will create a PostgresqlDatabase
instance. A username and password are provided, as well as the host and port to connect to.
• mysql://user:passwd@ip:port/my_db will create a MySQLDatabase instance for the local MySQL
database my_db.
• mysql+pool://user:passwd@ip:port/my_db?max_connections=20&stale_timeout=300 will create a
PooledMySQLDatabase instance for the local MySQL database my_db with max_connections set to 20
and a stale_timeout setting of 300 seconds.
Supported schemes:
• apsw: APSWDatabase
• mysql: MySQLDatabase
• mysql+pool: PooledMySQLDatabase
• postgres: PostgresqlDatabase
• postgres+pool: PooledPostgresqlDatabase
• postgresext: PostgresqlExtDatabase
• postgresext+pool: PooledPostgresqlExtDatabase
• sqlite: SqliteDatabase
• sqliteext: SqliteExtDatabase
• sqlite+pool: PooledSqliteDatabase
• sqliteext+pool: PooledSqliteExtDatabase
Usage:
import os
from playhouse.db_url import connect
# Connect to the database URL defined in the environment, falling
# back to a local Sqlite database if no database URL is specified.
db = connect(os.environ.get('DATABASE') or 'sqlite:///default.db')
parse(url)
Parse the information in the given URL into a dictionary containing database, host, port, user
and/or password. Additional connection arguments can be passed in the URL query string.
If you are using a custom database class, you can use the parse() function to extract information
from a URL which can then be passed in to your database object.
register_database(db_class, *names)
Parameters
• db_class -- A subclass of Database.
• names -- A list of names to use as the scheme in the URL, e.g. 'sqlite' or 'firebird'
Register additional database class under the specified names. This function can be used to extend
the connect() function to support additional schemes. Suppose you have a custom database class for
Firebird named FirebirdDatabase.
from playhouse.db_url import connect, register_database
register_database(FirebirdDatabase, 'firebird')
db = connect('firebird://my-firebird-db')
Connection pool
The pool module contains a number of Database classes that provide connection pooling for PostgreSQL,
MySQL and SQLite databases. The pool works by overriding the methods on the Database class that open and
close connections to the backend. The pool can specify a timeout after which connections are recycled, as
well as an upper bound on the number of open connections.
In a multi-threaded application, up to max_connections will be opened. Each thread (or, if using gevent,
greenlet) will have it's own connection.
In a single-threaded application, only one connection will be created. It will be continually recycled
until either it exceeds the stale timeout or is closed explicitly (using .manual_close()).
By default, all your application needs to do is ensure that connections are closed when you are finished
with them, and they will be returned to the pool. For web applications, this typically means that at the
beginning of a request, you will open a connection, and when you return a response, you will close the
connection.
Simple Postgres pool example code:
# Use the special postgresql extensions.
from playhouse.pool import PooledPostgresqlExtDatabase
db = PooledPostgresqlExtDatabase(
'my_app',
max_connections=32,
stale_timeout=300, # 5 minutes.
user='postgres')
class BaseModel(Model):
class Meta:
database = db
That's it! If you would like finer-grained control over the pool of connections, check out the
advanced_connection_management section.
Pool APIs
class PooledDatabase(database[, max_connections=20[, stale_timeout=None[, timeout=None[, **kwargs]]]])
Parameters
• database (str) -- The name of the database or database file.
• max_connections (int) -- Maximum number of connections. Provide None for unlimited.
• stale_timeout (int) -- Number of seconds to allow connections to be used.
• timeout (int) -- Number of seconds to block when pool is full. By default peewee does not
block when the pool is full but simply throws an exception. To block indefinitely set
this value to 0.
• kwargs -- Arbitrary keyword arguments passed to database class.
Mixin class intended to be used with a subclass of Database.
NOTE:
Connections will not be closed exactly when they exceed their stale_timeout. Instead, stale
connections are only closed when a new connection is requested.
NOTE:
If the number of open connections exceeds max_connections, a ValueError will be raised.
manual_close()
Close the currently-open connection without returning it to the pool.
close_idle()
Close all idle connections. This does not include any connections that are currently in-use
-- only those that were previously created but have since been returned back to the pool.
close_stale([age=600])
Parameters
age (int) -- Age at which a connection should be considered stale.
Returns
Number of connections closed.
Close connections which are in-use but exceed the given age. Use caution when calling this
method!
close_all()
Close all connections. This includes any connections that may be in use at the time. Use
caution when calling this method!
class PooledPostgresqlDatabase
Subclass of PostgresqlDatabase that mixes in the PooledDatabase helper.
class PooledPostgresqlExtDatabase
Subclass of PostgresqlExtDatabase that mixes in the PooledDatabase helper. The
PostgresqlExtDatabase is a part of the Postgresql Extensions module and provides support for many
Postgres-specific features.
class PooledMySQLDatabase
Subclass of MySQLDatabase that mixes in the PooledDatabase helper.
class PooledSqliteDatabase
Persistent connections for SQLite apps.
class PooledSqliteExtDatabase
Persistent connections for SQLite apps, using the sqlite_ext advanced database driver
SqliteExtDatabase.
Test Utils
Contains utilities helpful when testing peewee projects.
class count_queries([only_select=False])
Context manager that will count the number of queries executed within the context.
Parameters
only_select (bool) -- Only count SELECT queries.
with count_queries() as counter:
huey = User.get(User.username == 'huey')
huey_tweets = [tweet.message for tweet in huey.tweets]
assert counter.count == 2
count The number of queries executed.
get_queries()
Return a list of 2-tuples consisting of the SQL query and a list of parameters.
assert_query_count(expected[, only_select=False])
Function or method decorator that will raise an AssertionError if the number of queries executed
in the decorated function does not equal the expected number.
class TestMyApp(unittest.TestCase):
@assert_query_count(1)
def test_get_popular_blogs(self):
popular_blogs = Blog.get_popular()
self.assertEqual(
[blog.title for blog in popular_blogs],
["Peewee's Playhouse!", "All About Huey", "Mickey's Adventures"])
This function can also be used as a context manager:
class TestMyApp(unittest.TestCase):
def test_expensive_operation(self):
with assert_query_count(1):
perform_expensive_operation()
Flask Utils
The playhouse.flask_utils module contains several helpers for integrating peewee with the Flask web
framework.
Database Wrapper
The FlaskDB class is a wrapper for configuring and referencing a Peewee database from within a Flask
application. Don't let it's name fool you: it is not the same thing as a peewee database. FlaskDB is
designed to remove the following boilerplate from your flask app:
• Dynamically create a Peewee database instance based on app config data.
• Create a base class from which all your application's models will descend.
• Register hooks at the start and end of a request to handle opening and closing a database connection.
Basic usage:
import datetime
from flask import Flask
from peewee import *
from playhouse.flask_utils import FlaskDB
DATABASE = 'postgresql://postgres:password@localhost:5432/my_database'
app = Flask(__name__)
app.config.from_object(__name__)
db_wrapper = FlaskDB(app)
class User(db_wrapper.Model):
username = CharField(unique=True)
class Tweet(db_wrapper.Model):
user = ForeignKeyField(User, backref='tweets')
content = TextField()
timestamp = DateTimeField(default=datetime.datetime.now)
The above code example will create and instantiate a peewee PostgresqlDatabase specified by the given
database URL. Request hooks will be configured to establish a connection when a request is received, and
automatically close the connection when the response is sent. Lastly, the FlaskDB class exposes a
FlaskDB.Model property which can be used as a base for your application's models.
Here is how you can access the wrapped Peewee database instance that is configured for you by the FlaskDB
wrapper:
# Obtain a reference to the Peewee database instance.
peewee_db = db_wrapper.database
@app.route('/transfer-funds/', methods=['POST'])
def transfer_funds():
with peewee_db.atomic():
# ...
return jsonify({'transfer-id': xid})
NOTE:
The actual peewee database can be accessed using the FlaskDB.database attribute.
Here is another way to configure a Peewee database using FlaskDB:
app = Flask(__name__)
db_wrapper = FlaskDB(app, 'sqlite:///my_app.db')
While the above examples show using a database URL, for more advanced usages you can specify a dictionary
of configuration options, or simply pass in a peewee Database instance:
DATABASE = {
'name': 'my_app_db',
'engine': 'playhouse.pool.PooledPostgresqlDatabase',
'user': 'postgres',
'max_connections': 32,
'stale_timeout': 600,
}
app = Flask(__name__)
app.config.from_object(__name__)
wrapper = FlaskDB(app)
pooled_postgres_db = wrapper.database
Using a peewee Database object:
peewee_db = PostgresqlExtDatabase('my_app')
app = Flask(__name__)
db_wrapper = FlaskDB(app, peewee_db)
Database with Application Factory
If you prefer to use the application factory pattern, the FlaskDB class implements an init_app() method.
Using as a factory:
db_wrapper = FlaskDB()
# Even though the database is not yet initialized, you can still use the
# `Model` property to create model classes.
class User(db_wrapper.Model):
username = CharField(unique=True)
def create_app():
app = Flask(__name__)
app.config['DATABASE'] = 'sqlite:////home/code/apps/my-database.db'
db_wrapper.init_app(app)
return app
Query utilities
The flask_utils module provides several helpers for managing queries in your web app. Some common
patterns include:
get_object_or_404(query_or_model, *query)
Parameters
• query_or_model -- Either a Model class or a pre-filtered SelectQuery.
• query -- An arbitrarily complex peewee expression.
Retrieve the object matching the given query, or return a 404 not found response. A common
use-case might be a detail page for a weblog. You want to either retrieve the post matching the
given URL, or return a 404.
Example:
@app.route('/blog/<slug>/')
def post_detail(slug):
public_posts = Post.select().where(Post.published == True)
post = get_object_or_404(public_posts, (Post.slug == slug))
return render_template('post_detail.html', post=post)
object_list(template_name, query[, context_variable='object_list'[, paginate_by=20[, page_var='page'[,
check_bounds=True[, **kwargs]]]]])
Parameters
• template_name -- The name of the template to render.
• query -- A SelectQuery instance to paginate.
• context_variable -- The context variable name to use for the paginated object list.
• paginate_by -- Number of objects per-page.
• page_var -- The name of the GET argument which contains the page.
• check_bounds -- Whether to check that the given page is a valid page. If check_bounds is
True and an invalid page is specified, then a 404 will be returned.
• kwargs -- Arbitrary key/value pairs to pass into the template context.
Retrieve a paginated list of objects specified by the given query. The paginated object list will
be dropped into the context using the given context_variable, as well as metadata about the
current page and total number of pages, and finally any arbitrary context data passed as
keyword-arguments.
The page is specified using the page GET argument, e.g. /my-object-list/?page=3 would return the
third page of objects.
Example:
@app.route('/blog/')
def post_index():
public_posts = (Post
.select()
.where(Post.published == True)
.order_by(Post.timestamp.desc()))
return object_list(
'post_index.html',
query=public_posts,
context_variable='post_list',
paginate_by=10)
The template will have the following context:
• post_list, which contains a list of up to 10 posts.
• page, which contains the current page based on the value of the page GET parameter.
• pagination, a PaginatedQuery instance.
class PaginatedQuery(query_or_model, paginate_by[, page_var='page'[, check_bounds=False]])
Parameters
• query_or_model -- Either a Model or a SelectQuery instance containing the collection of
records you wish to paginate.
• paginate_by -- Number of objects per-page.
• page_var -- The name of the GET argument which contains the page.
• check_bounds -- Whether to check that the given page is a valid page. If check_bounds is
True and an invalid page is specified, then a 404 will be returned.
Helper class to perform pagination based on GET arguments.
get_page()
Return the currently selected page, as indicated by the value of the page_var GET
parameter. If no page is explicitly selected, then this method will return 1, indicating
the first page.
get_page_count()
Return the total number of possible pages.
get_object_list()
Using the value of get_page(), return the page of objects requested by the user. The return
value is a SelectQuery with the appropriate LIMIT and OFFSET clauses.
If check_bounds was set to True and the requested page contains no objects, then a 404 will
be raised.
Query Examples
These query examples are taken from the site PostgreSQL Exercises. A sample data-set can be found on the
getting started page.
Here is a visual representation of the schema used in these examples: [image]
Model Definitions
To begin working with the data, we'll define the model classes that correspond to the tables in the
diagram.
NOTE:
In some cases we explicitly specify column names for a particular field. This is so our models are
compatible with the database schema used for the postgres exercises.
from functools import partial
from peewee import *
db = PostgresqlDatabase('peewee_test')
class BaseModel(Model):
class Meta:
database = db
class Member(BaseModel):
memid = AutoField() # Auto-incrementing primary key.
surname = CharField()
firstname = CharField()
address = CharField(max_length=300)
zipcode = IntegerField()
telephone = CharField()
recommendedby = ForeignKeyField('self', backref='recommended',
column_name='recommendedby', null=True)
joindate = DateTimeField()
class Meta:
table_name = 'members'
# Conveniently declare decimal fields suitable for storing currency.
MoneyField = partial(DecimalField, decimal_places=2)
class Facility(BaseModel):
facid = AutoField()
name = CharField()
membercost = MoneyField()
guestcost = MoneyField()
initialoutlay = MoneyField()
monthlymaintenance = MoneyField()
class Meta:
table_name = 'facilities'
class Booking(BaseModel):
bookid = AutoField()
facility = ForeignKeyField(Facility, column_name='facid')
member = ForeignKeyField(Member, column_name='memid')
starttime = DateTimeField()
slots = IntegerField()
class Meta:
table_name = 'bookings'
Schema Creation
If you downloaded the SQL file from the PostgreSQL Exercises site, then you can load the data into a
PostgreSQL database using the following commands:
createdb peewee_test
psql -U postgres -f clubdata.sql -d peewee_test -x -q
To create the schema using Peewee, without loading the sample data, you can run the following:
# Assumes you have created the database "peewee_test" already.
db.create_tables([Member, Facility, Booking])
Basic Exercises
This category deals with the basics of SQL. It covers select and where clauses, case expressions, unions,
and a few other odds and ends.
Retrieve everything
Retrieve all information from facilities table.
SELECT * FROM facilities
# By default, when no fields are explicitly passed to select(), all fields
# will be selected.
query = Facility.select()
Retrieve specific columns from a table
Retrieve names of facilities and cost to members.
SELECT name, membercost FROM facilities;
query = Facility.select(Facility.name, Facility.membercost)
# To iterate:
for facility in query:
print(facility.name)
Control which rows are retrieved
Retrieve list of facilities that have a cost to members.
SELECT * FROM facilities WHERE membercost > 0
query = Facility.select().where(Facility.membercost > 0)
Control which rows are retrieved - part 2
Retrieve list of facilities that have a cost to members, and that fee is less than 1/50th of the monthly
maintenance cost. Return id, name, cost and monthly-maintenance.
SELECT facid, name, membercost, monthlymaintenance
FROM facilities
WHERE membercost > 0 AND membercost < (monthlymaintenance / 50)
query = (Facility
.select(Facility.facid, Facility.name, Facility.membercost,
Facility.monthlymaintenance)
.where(
(Facility.membercost > 0) &
(Facility.membercost < (Facility.monthlymaintenance / 50))))
Basic string searches
How can you produce a list of all facilities with the word 'Tennis' in their name?
SELECT * FROM facilities WHERE name ILIKE '%tennis%';
query = Facility.select().where(Facility.name.contains('tennis'))
# OR use the exponent operator. Note: you must include wildcards here:
query = Facility.select().where(Facility.name ** '%tennis%')
Matching against multiple possible values
How can you retrieve the details of facilities with ID 1 and 5? Try to do it without using the OR
operator.
SELECT * FROM facilities WHERE facid IN (1, 5);
query = Facility.select().where(Facility.facid.in_([1, 5]))
# OR:
query = Facility.select().where((Facility.facid == 1) |
(Facility.facid == 5))
Classify results into buckets
How can you produce a list of facilities, with each labelled as 'cheap' or 'expensive' depending on if
their monthly maintenance cost is more than $100? Return the name and monthly maintenance of the
facilities in question.
SELECT name,
CASE WHEN monthlymaintenance > 100 THEN 'expensive' ELSE 'cheap' END
FROM facilities;
cost = Case(None, [(Facility.monthlymaintenance > 100, 'expensive')], 'cheap')
query = Facility.select(Facility.name, cost.alias('cost'))
NOTE:
See documentation Case for more examples.
Working with dates
How can you produce a list of members who joined after the start of September 2012? Return the memid,
surname, firstname, and joindate of the members in question.
SELECT memid, surname, firstname, joindate FROM members
WHERE joindate >= '2012-09-01';
query = (Member
.select(Member.memid, Member.surname, Member.firstname, Member.joindate)
.where(Member.joindate >= datetime.date(2012, 9, 1)))
Removing duplicates, and ordering results
How can you produce an ordered list of the first 10 surnames in the members table? The list must not
contain duplicates.
SELECT DISTINCT surname FROM members ORDER BY surname LIMIT 10;
query = (Member
.select(Member.surname)
.order_by(Member.surname)
.limit(10)
.distinct())
Combining results from multiple queries
You, for some reason, want a combined list of all surnames and all facility names.
SELECT surname FROM members UNION SELECT name FROM facilities;
lhs = Member.select(Member.surname)
rhs = Facility.select(Facility.name)
query = lhs | rhs
Queries can be composed using the following operators:
• | - UNION
• + - UNION ALL
• & - INTERSECT
• - - EXCEPT
Simple aggregation
You'd like to get the signup date of your last member. How can you retrieve this information?
SELECT MAX(join_date) FROM members;
query = Member.select(fn.MAX(Member.joindate))
# To conveniently obtain a single scalar value, use "scalar()":
# max_join_date = query.scalar()
More aggregation
You'd like to get the first and last name of the last member(s) who signed up - not just the date.
SELECT firstname, surname, joindate FROM members
WHERE joindate = (SELECT MAX(joindate) FROM members);
# Use "alias()" to reference the same table multiple times in a query.
MemberAlias = Member.alias()
subq = MemberAlias.select(fn.MAX(MemberAlias.joindate))
query = (Member
.select(Member.firstname, Member.surname, Member.joindate)
.where(Member.joindate == subq))
Joins and Subqueries
This category deals primarily with a foundational concept in relational database systems: joining.
Joining allows you to combine related information from multiple tables to answer a question. This isn't
just beneficial for ease of querying: a lack of join capability encourages denormalisation of data, which
increases the complexity of keeping your data internally consistent.
This topic covers inner, outer, and self joins, as well as spending a little time on subqueries (queries
within queries).
Retrieve the start times of members' bookings
How can you produce a list of the start times for bookings by members named 'David Farrell'?
SELECT starttime FROM bookings
INNER JOIN members ON (bookings.memid = members.memid)
WHERE surname = 'Farrell' AND firstname = 'David';
query = (Booking
.select(Booking.starttime)
.join(Member)
.where((Member.surname == 'Farrell') &
(Member.firstname == 'David')))
Work out the start times of bookings for tennis courts
How can you produce a list of the start times for bookings for tennis courts, for the date '2012-09-21'?
Return a list of start time and facility name pairings, ordered by the time.
SELECT starttime, name
FROM bookings
INNER JOIN facilities ON (bookings.facid = facilities.facid)
WHERE date_trunc('day', starttime) = '2012-09-21':: date
AND name ILIKE 'tennis%'
ORDER BY starttime, name;
query = (Booking
.select(Booking.starttime, Facility.name)
.join(Facility)
.where(
(fn.date_trunc('day', Booking.starttime) == datetime.date(2012, 9, 21)) &
Facility.name.startswith('Tennis'))
.order_by(Booking.starttime, Facility.name))
# To retrieve the joined facility's name when iterating:
for booking in query:
print(booking.starttime, booking.facility.name)
Produce a list of all members who have recommended another member
How can you output a list of all members who have recommended another member? Ensure that there are no
duplicates in the list, and that results are ordered by (surname, firstname).
SELECT DISTINCT m.firstname, m.surname
FROM members AS m2
INNER JOIN members AS m ON (m.memid = m2.recommendedby)
ORDER BY m.surname, m.firstname;
MA = Member.alias()
query = (Member
.select(Member.firstname, Member.surname)
.join(MA, on=(MA.recommendedby == Member.memid))
.order_by(Member.surname, Member.firstname))
Produce a list of all members, along with their recommender
How can you output a list of all members, including the individual who recommended them (if any)? Ensure
that results are ordered by (surname, firstname).
SELECT m.firstname, m.surname, r.firstname, r.surname
FROM members AS m
LEFT OUTER JOIN members AS r ON (m.recommendedby = r.memid)
ORDER BY m.surname, m.firstname
MA = Member.alias()
query = (Member
.select(Member.firstname, Member.surname, MA.firstname, MA.surname)
.join(MA, JOIN.LEFT_OUTER, on=(Member.recommendedby == MA.memid))
.order_by(Member.surname, Member.firstname))
# To display the recommender's name when iterating:
for m in query:
print(m.firstname, m.surname)
if m.recommendedby:
print(' ', m.recommendedby.firstname, m.recommendedby.surname)
Produce a list of all members who have used a tennis court
How can you produce a list of all members who have used a tennis court? Include in your output the name
of the court, and the name of the member formatted as a single column. Ensure no duplicate data, and
order by the member name.
SELECT DISTINCT m.firstname || ' ' || m.surname AS member, f.name AS facility
FROM members AS m
INNER JOIN bookings AS b ON (m.memid = b.memid)
INNER JOIN facilities AS f ON (b.facid = f.facid)
WHERE f.name LIKE 'Tennis%'
ORDER BY member, facility;
fullname = Member.firstname + ' ' + Member.surname
query = (Member
.select(fullname.alias('member'), Facility.name.alias('facility'))
.join(Booking)
.join(Facility)
.where(Facility.name.startswith('Tennis'))
.order_by(fullname, Facility.name)
.distinct())
Produce a list of costly bookings
How can you produce a list of bookings on the day of 2012-09-14 which will cost the member (or guest)
more than $30? Remember that guests have different costs to members (the listed costs are per half-hour
'slot'), and the guest user is always ID 0. Include in your output the name of the facility, the name of
the member formatted as a single column, and the cost. Order by descending cost, and do not use any
subqueries.
SELECT m.firstname || ' ' || m.surname AS member,
f.name AS facility,
(CASE WHEN m.memid = 0 THEN f.guestcost * b.slots
ELSE f.membercost * b.slots END) AS cost
FROM members AS m
INNER JOIN bookings AS b ON (m.memid = b.memid)
INNER JOIN facilities AS f ON (b.facid = f.facid)
WHERE (date_trunc('day', b.starttime) = '2012-09-14') AND
((m.memid = 0 AND b.slots * f.guestcost > 30) OR
(m.memid > 0 AND b.slots * f.membercost > 30))
ORDER BY cost DESC;
cost = Case(Member.memid, (
(0, Booking.slots * Facility.guestcost),
), (Booking.slots * Facility.membercost))
fullname = Member.firstname + ' ' + Member.surname
query = (Member
.select(fullname.alias('member'), Facility.name.alias('facility'),
cost.alias('cost'))
.join(Booking)
.join(Facility)
.where(
(fn.date_trunc('day', Booking.starttime) == datetime.date(2012, 9, 14)) &
(cost > 30))
.order_by(SQL('cost').desc()))
# To iterate over the results, it might be easiest to use namedtuples:
for row in query.namedtuples():
print(row.member, row.facility, row.cost)
Produce a list of all members, along with their recommender, using no joins.
How can you output a list of all members, including the individual who recommended them (if any), without
using any joins? Ensure that there are no duplicates in the list, and that each firstname + surname
pairing is formatted as a column and ordered.
SELECT DISTINCT m.firstname || ' ' || m.surname AS member,
(SELECT r.firstname || ' ' || r.surname
FROM cd.members AS r
WHERE m.recommendedby = r.memid) AS recommended
FROM members AS m ORDER BY member;
MA = Member.alias()
subq = (MA
.select(MA.firstname + ' ' + MA.surname)
.where(Member.recommendedby == MA.memid))
query = (Member
.select(fullname.alias('member'), subq.alias('recommended'))
.order_by(fullname))
Produce a list of costly bookings, using a subquery
The "Produce a list of costly bookings" exercise contained some messy logic: we had to calculate the
booking cost in both the WHERE clause and the CASE statement. Try to simplify this calculation using
subqueries.
SELECT member, facility, cost from (
SELECT
m.firstname || ' ' || m.surname as member,
f.name as facility,
CASE WHEN m.memid = 0 THEN b.slots * f.guestcost
ELSE b.slots * f.membercost END AS cost
FROM members AS m
INNER JOIN bookings AS b ON m.memid = b.memid
INNER JOIN facilities AS f ON b.facid = f.facid
WHERE date_trunc('day', b.starttime) = '2012-09-14'
) as bookings
WHERE cost > 30
ORDER BY cost DESC;
cost = Case(Member.memid, (
(0, Booking.slots * Facility.guestcost),
), (Booking.slots * Facility.membercost))
iq = (Member
.select(fullname.alias('member'), Facility.name.alias('facility'),
cost.alias('cost'))
.join(Booking)
.join(Facility)
.where(fn.date_trunc('day', Booking.starttime) == datetime.date(2012, 9, 14)))
query = (Member
.select(iq.c.member, iq.c.facility, iq.c.cost)
.from_(iq)
.where(iq.c.cost > 30)
.order_by(SQL('cost').desc()))
# To iterate, try using dicts:
for row in query.dicts():
print(row['member'], row['facility'], row['cost'])
Modifying Data
Querying data is all well and good, but at some point you're probably going to want to put data into your
database! This section deals with inserting, updating, and deleting information. Operations that alter
your data like this are collectively known as Data Manipulation Language, or DML.
In previous sections, we returned to you the results of the query you've performed. Since modifications
like the ones we're making in this section don't return any query results, we instead show you the
updated content of the table you're supposed to be working on.
Insert some data into a table
The club is adding a new facility - a spa. We need to add it into the facilities table. Use the following
values: facid: 9, Name: 'Spa', membercost: 20, guestcost: 30, initialoutlay: 100000, monthlymaintenance:
800
INSERT INTO "facilities" ("facid", "name", "membercost", "guestcost",
"initialoutlay", "monthlymaintenance") VALUES (9, 'Spa', 20, 30, 100000, 800)
res = Facility.insert({
Facility.facid: 9,
Facility.name: 'Spa',
Facility.membercost: 20,
Facility.guestcost: 30,
Facility.initialoutlay: 100000,
Facility.monthlymaintenance: 800}).execute()
# OR:
res = (Facility
.insert(facid=9, name='Spa', membercost=20, guestcost=30,
initialoutlay=100000, monthlymaintenance=800)
.execute())
Insert multiple rows of data into a table
In the previous exercise, you learned how to add a facility. Now you're going to add multiple facilities
in one command. Use the following values:
facid: 9, Name: 'Spa', membercost: 20, guestcost: 30, initialoutlay: 100000, monthlymaintenance: 800.
facid: 10, Name: 'Squash Court 2', membercost: 3.5, guestcost: 17.5, initialoutlay: 5000,
monthlymaintenance: 80.
-- see above --
data = [
{'facid': 9, 'name': 'Spa', 'membercost': 20, 'guestcost': 30,
'initialoutlay': 100000, 'monthlymaintenance': 800},
{'facid': 10, 'name': 'Squash Court 2', 'membercost': 3.5,
'guestcost': 17.5, 'initialoutlay': 5000, 'monthlymaintenance': 80}]
res = Facility.insert_many(data).execute()
Insert calculated data into a table
Let's try adding the spa to the facilities table again. This time, though, we want to automatically
generate the value for the next facid, rather than specifying it as a constant. Use the following values
for everything else: Name: 'Spa', membercost: 20, guestcost: 30, initialoutlay: 100000,
monthlymaintenance: 800.
INSERT INTO "facilities" ("facid", "name", "membercost", "guestcost",
"initialoutlay", "monthlymaintenance")
SELECT (SELECT (MAX("facid") + 1) FROM "facilities") AS _,
'Spa', 20, 30, 100000, 800;
maxq = Facility.select(fn.MAX(Facility.facid) + 1)
subq = Select(columns=(maxq, 'Spa', 20, 30, 100000, 800))
res = Facility.insert_from(subq, Facility._meta.sorted_fields).execute()
Update some existing data
We made a mistake when entering the data for the second tennis court. The initial outlay was 10000 rather
than 8000: you need to alter the data to fix the error.
UPDATE facilities SET initialoutlay = 10000 WHERE name = 'Tennis Court 2';
res = (Facility
.update({Facility.initialoutlay: 10000})
.where(Facility.name == 'Tennis Court 2')
.execute())
# OR:
res = (Facility
.update(initialoutlay=10000)
.where(Facility.name == 'Tennis Court 2')
.execute())
Update multiple rows and columns at the same time
We want to increase the price of the tennis courts for both members and guests. Update the costs to be 6
for members, and 30 for guests.
UPDATE facilities SET membercost=6, guestcost=30 WHERE name ILIKE 'Tennis%';
nrows = (Facility
.update(membercost=6, guestcost=30)
.where(Facility.name.startswith('Tennis'))
.execute())
Update a row based on the contents of another row
We want to alter the price of the second tennis court so that it costs 10% more than the first one. Try
to do this without using constant values for the prices, so that we can reuse the statement if we want
to.
UPDATE facilities SET
membercost = (SELECT membercost * 1.1 FROM facilities WHERE facid = 0),
guestcost = (SELECT guestcost * 1.1 FROM facilities WHERE facid = 0)
WHERE facid = 1;
-- OR --
WITH new_prices (nmc, ngc) AS (
SELECT membercost * 1.1, guestcost * 1.1
FROM facilities WHERE name = 'Tennis Court 1')
UPDATE facilities
SET membercost = new_prices.nmc, guestcost = new_prices.ngc
FROM new_prices
WHERE name = 'Tennis Court 2'
sq1 = Facility.select(Facility.membercost * 1.1).where(Facility.facid == 0)
sq2 = Facility.select(Facility.guestcost * 1.1).where(Facility.facid == 0)
res = (Facility
.update(membercost=sq1, guestcost=sq2)
.where(Facility.facid == 1)
.execute())
# OR:
cte = (Facility
.select(Facility.membercost * 1.1, Facility.guestcost * 1.1)
.where(Facility.name == 'Tennis Court 1')
.cte('new_prices', columns=('nmc', 'ngc')))
res = (Facility
.update(membercost=SQL('new_prices.nmc'), guestcost=SQL('new_prices.ngc'))
.with_cte(cte)
.from_(cte)
.where(Facility.name == 'Tennis Court 2')
.execute())
Delete all bookings
As part of a clearout of our database, we want to delete all bookings from the bookings table.
DELETE FROM bookings;
nrows = Booking.delete().execute()
Delete a member from the cd.members table
We want to remove member 37, who has never made a booking, from our database.
DELETE FROM members WHERE memid = 37;
nrows = Member.delete().where(Member.memid == 37).execute()
Delete based on a subquery
How can we make that more general, to delete all members who have never made a booking?
DELETE FROM members WHERE NOT EXISTS (
SELECT * FROM bookings WHERE bookings.memid = members.memid);
subq = Booking.select().where(Booking.member == Member.memid)
nrows = Member.delete().where(~fn.EXISTS(subq)).execute()
Aggregation
Aggregation is one of those capabilities that really make you appreciate the power of relational database
systems. It allows you to move beyond merely persisting your data, into the realm of asking truly
interesting questions that can be used to inform decision making. This category covers aggregation at
length, making use of standard grouping as well as more recent window functions.
Count the number of facilities
For our first foray into aggregates, we're going to stick to something simple. We want to know how many
facilities exist - simply produce a total count.
SELECT COUNT(facid) FROM facilities;
query = Facility.select(fn.COUNT(Facility.facid))
count = query.scalar()
# OR:
count = Facility.select().count()
Count the number of expensive facilities
Produce a count of the number of facilities that have a cost to guests of 10 or more.
SELECT COUNT(facid) FROM facilities WHERE guestcost >= 10
query = Facility.select(fn.COUNT(Facility.facid)).where(Facility.guestcost >= 10)
count = query.scalar()
# OR:
# count = Facility.select().where(Facility.guestcost >= 10).count()
Count the number of recommendations each member makes.
Produce a count of the number of recommendations each member has made. Order by member ID.
SELECT recommendedby, COUNT(memid) FROM members
WHERE recommendedby IS NOT NULL
GROUP BY recommendedby
ORDER BY recommendedby
query = (Member
.select(Member.recommendedby, fn.COUNT(Member.memid))
.where(Member.recommendedby.is_null(False))
.group_by(Member.recommendedby)
.order_by(Member.recommendedby))
List the total slots booked per facility
Produce a list of the total number of slots booked per facility. For now, just produce an output table
consisting of facility id and slots, sorted by facility id.
SELECT facid, SUM(slots) FROM bookings GROUP BY facid ORDER BY facid;
query = (Booking
.select(Booking.facid, fn.SUM(Booking.slots))
.group_by(Booking.facid)
.order_by(Booking.facid))
List the total slots booked per facility in a given month
Produce a list of the total number of slots booked per facility in the month of September 2012. Produce
an output table consisting of facility id and slots, sorted by the number of slots.
SELECT facid, SUM(slots)
FROM bookings
WHERE (date_trunc('month', starttime) = '2012-09-01'::dates)
GROUP BY facid
ORDER BY SUM(slots)
query = (Booking
.select(Booking.facility, fn.SUM(Booking.slots))
.where(fn.date_trunc('month', Booking.starttime) == datetime.date(2012, 9, 1))
.group_by(Booking.facility)
.order_by(fn.SUM(Booking.slots)))
List the total slots booked per facility per month
Produce a list of the total number of slots booked per facility per month in the year of 2012. Produce an
output table consisting of facility id and slots, sorted by the id and month.
SELECT facid, date_part('month', starttime), SUM(slots)
FROM bookings
WHERE date_part('year', starttime) = 2012
GROUP BY facid, date_part('month', starttime)
ORDER BY facid, date_part('month', starttime)
month = fn.date_part('month', Booking.starttime)
query = (Booking
.select(Booking.facility, month, fn.SUM(Booking.slots))
.where(fn.date_part('year', Booking.starttime) == 2012)
.group_by(Booking.facility, month)
.order_by(Booking.facility, month))
Find the count of members who have made at least one booking
Find the total number of members who have made at least one booking.
SELECT COUNT(DISTINCT memid) FROM bookings
-- OR --
SELECT COUNT(1) FROM (SELECT DISTINCT memid FROM bookings) AS _
query = Booking.select(fn.COUNT(Booking.member.distinct()))
# OR:
query = Booking.select(Booking.member).distinct()
count = query.count() # count() wraps in SELECT COUNT(1) FROM (...)
List facilities with more than 1000 slots booked
Produce a list of facilities with more than 1000 slots booked. Produce an output table consisting of
facility id and hours, sorted by facility id.
SELECT facid, SUM(slots) FROM bookings
GROUP BY facid
HAVING SUM(slots) > 1000
ORDER BY facid;
query = (Booking
.select(Booking.facility, fn.SUM(Booking.slots))
.group_by(Booking.facility)
.having(fn.SUM(Booking.slots) > 1000)
.order_by(Booking.facility))
Find the total revenue of each facility
Produce a list of facilities along with their total revenue. The output table should consist of facility
name and revenue, sorted by revenue. Remember that there's a different cost for guests and members!
SELECT f.name, SUM(b.slots * (
CASE WHEN b.memid = 0 THEN f.guestcost ELSE f.membercost END)) AS revenue
FROM bookings AS b
INNER JOIN facilities AS f ON b.facid = f.facid
GROUP BY f.name
ORDER BY revenue;
revenue = fn.SUM(Booking.slots * Case(None, (
(Booking.member == 0, Facility.guestcost),
), Facility.membercost))
query = (Facility
.select(Facility.name, revenue.alias('revenue'))
.join(Booking)
.group_by(Facility.name)
.order_by(SQL('revenue')))
Find facilities with a total revenue less than 1000
Produce a list of facilities with a total revenue less than 1000. Produce an output table consisting of
facility name and revenue, sorted by revenue. Remember that there's a different cost for guests and
members!
SELECT f.name, SUM(b.slots * (
CASE WHEN b.memid = 0 THEN f.guestcost ELSE f.membercost END)) AS revenue
FROM bookings AS b
INNER JOIN facilities AS f ON b.facid = f.facid
GROUP BY f.name
HAVING SUM(b.slots * ...) < 1000
ORDER BY revenue;
# Same definition as previous example.
revenue = fn.SUM(Booking.slots * Case(None, (
(Booking.member == 0, Facility.guestcost),
), Facility.membercost))
query = (Facility
.select(Facility.name, revenue.alias('revenue'))
.join(Booking)
.group_by(Facility.name)
.having(revenue < 1000)
.order_by(SQL('revenue')))
Output the facility id that has the highest number of slots booked
Output the facility id that has the highest number of slots booked.
SELECT facid, SUM(slots) FROM bookings
GROUP BY facid
ORDER BY SUM(slots) DESC
LIMIT 1
query = (Booking
.select(Booking.facility, fn.SUM(Booking.slots))
.group_by(Booking.facility)
.order_by(fn.SUM(Booking.slots).desc())
.limit(1))
# Retrieve multiple scalar values by calling scalar() with as_tuple=True.
facid, nslots = query.scalar(as_tuple=True)
List the total slots booked per facility per month, part 2
Produce a list of the total number of slots booked per facility per month in the year of 2012. In this
version, include output rows containing totals for all months per facility, and a total for all months
for all facilities. The output table should consist of facility id, month and slots, sorted by the id and
month. When calculating the aggregated values for all months and all facids, return null values in the
month and facid columns.
Postgres ONLY.
SELECT facid, date_part('month', starttime), SUM(slots)
FROM booking
WHERE date_part('year', starttime) = 2012
GROUP BY ROLLUP(facid, date_part('month', starttime))
ORDER BY facid, date_part('month', starttime)
month = fn.date_part('month', Booking.starttime)
query = (Booking
.select(Booking.facility,
month.alias('month'),
fn.SUM(Booking.slots))
.where(fn.date_part('year', Booking.starttime) == 2012)
.group_by(fn.ROLLUP(Booking.facility, month))
.order_by(Booking.facility, month))
List the total hours booked per named facility
Produce a list of the total number of hours booked per facility, remembering that a slot lasts half an
hour. The output table should consist of the facility id, name, and hours booked, sorted by facility id.
SELECT f.facid, f.name, SUM(b.slots) * .5
FROM facilities AS f
INNER JOIN bookings AS b ON (f.facid = b.facid)
GROUP BY f.facid, f.name
ORDER BY f.facid
query = (Facility
.select(Facility.facid, Facility.name, fn.SUM(Booking.slots) * .5)
.join(Booking)
.group_by(Facility.facid, Facility.name)
.order_by(Facility.facid))
List each member's first booking after September 1st 2012
Produce a list of each member name, id, and their first booking after September 1st 2012. Order by member
ID.
SELECT m.surname, m.firstname, m.memid, min(b.starttime) as starttime
FROM members AS m
INNER JOIN bookings AS b ON b.memid = m.memid
WHERE starttime >= '2012-09-01'
GROUP BY m.surname, m.firstname, m.memid
ORDER BY m.memid;
query = (Member
.select(Member.surname, Member.firstname, Member.memid,
fn.MIN(Booking.starttime).alias('starttime'))
.join(Booking)
.where(Booking.starttime >= datetime.date(2012, 9, 1))
.group_by(Member.surname, Member.firstname, Member.memid)
.order_by(Member.memid))
Produce a list of member names, with each row containing the total member count
Produce a list of member names, with each row containing the total member count. Order by join date.
Postgres ONLY (as written).
SELECT COUNT(*) OVER(), firstname, surname
FROM members ORDER BY joindate
query = (Member
.select(fn.COUNT(Member.memid).over(), Member.firstname,
Member.surname)
.order_by(Member.joindate))
Produce a numbered list of members
Produce a monotonically increasing numbered list of members, ordered by their date of joining. Remember
that member IDs are not guaranteed to be sequential.
Postgres ONLY (as written).
SELECT row_number() OVER (ORDER BY joindate), firstname, surname
FROM members ORDER BY joindate;
query = (Member
.select(fn.row_number().over(order_by=[Member.joindate]),
Member.firstname, Member.surname)
.order_by(Member.joindate))
Output the facility id that has the highest number of slots booked, again
Output the facility id that has the highest number of slots booked. Ensure that in the event of a tie,
all tieing results get output.
Postgres ONLY (as written).
SELECT facid, total FROM (
SELECT facid, SUM(slots) AS total,
rank() OVER (order by SUM(slots) DESC) AS rank
FROM bookings
GROUP BY facid
) AS ranked WHERE rank = 1
rank = fn.rank().over(order_by=[fn.SUM(Booking.slots).desc()])
subq = (Booking
.select(Booking.facility, fn.SUM(Booking.slots).alias('total'),
rank.alias('rank'))
.group_by(Booking.facility))
# Here we use a plain Select() to create our query.
query = (Select(columns=[subq.c.facid, subq.c.total])
.from_(subq)
.where(subq.c.rank == 1)
.bind(db)) # We must bind() it to the database.
# To iterate over the query results:
for facid, total in query.tuples():
print(facid, total)
Rank members by (rounded) hours used
Produce a list of members, along with the number of hours they've booked in facilities, rounded to the
nearest ten hours. Rank them by this rounded figure, producing output of first name, surname, rounded
hours, rank. Sort by rank, surname, and first name.
Postgres ONLY (as written).
SELECT firstname, surname,
((SUM(bks.slots)+10)/20)*10 as hours,
rank() over (order by ((sum(bks.slots)+10)/20)*10 desc) as rank
FROM members AS mems
INNER JOIN bookings AS bks ON mems.memid = bks.memid
GROUP BY mems.memid
ORDER BY rank, surname, firstname;
hours = ((fn.SUM(Booking.slots) + 10) / 20) * 10
query = (Member
.select(Member.firstname, Member.surname, hours.alias('hours'),
fn.rank().over(order_by=[hours.desc()]).alias('rank'))
.join(Booking)
.group_by(Member.memid)
.order_by(SQL('rank'), Member.surname, Member.firstname))
Find the top three revenue generating facilities
Produce a list of the top three revenue generating facilities (including ties). Output facility name and
rank, sorted by rank and facility name.
Postgres ONLY (as written).
SELECT name, rank FROM (
SELECT f.name, RANK() OVER (ORDER BY SUM(
CASE WHEN memid = 0 THEN slots * f.guestcost
ELSE slots * f.membercost END) DESC) AS rank
FROM bookings
INNER JOIN facilities AS f ON bookings.facid = f.facid
GROUP BY f.name) AS subq
WHERE rank <= 3
ORDER BY rank;
total_cost = fn.SUM(Case(None, (
(Booking.member == 0, Booking.slots * Facility.guestcost),
), (Booking.slots * Facility.membercost)))
subq = (Facility
.select(Facility.name,
fn.RANK().over(order_by=[total_cost.desc()]).alias('rank'))
.join(Booking)
.group_by(Facility.name))
query = (Select(columns=[subq.c.name, subq.c.rank])
.from_(subq)
.where(subq.c.rank <= 3)
.order_by(subq.c.rank)
.bind(db)) # Here again we used plain Select, and call bind().
Classify facilities by value
Classify facilities into equally sized groups of high, average, and low based on their revenue. Order by
classification and facility name.
Postgres ONLY (as written).
SELECT name,
CASE class WHEN 1 THEN 'high' WHEN 2 THEN 'average' ELSE 'low' END
FROM (
SELECT f.name, ntile(3) OVER (ORDER BY SUM(
CASE WHEN memid = 0 THEN slots * f.guestcost ELSE slots * f.membercost
END) DESC) AS class
FROM bookings INNER JOIN facilities AS f ON bookings.facid = f.facid
GROUP BY f.name
) AS subq
ORDER BY class, name;
cost = fn.SUM(Case(None, (
(Booking.member == 0, Booking.slots * Facility.guestcost),
), (Booking.slots * Facility.membercost)))
subq = (Facility
.select(Facility.name,
fn.NTILE(3).over(order_by=[cost.desc()]).alias('klass'))
.join(Booking)
.group_by(Facility.name))
klass_case = Case(subq.c.klass, [(1, 'high'), (2, 'average')], 'low')
query = (Select(columns=[subq.c.name, klass_case])
.from_(subq)
.order_by(subq.c.klass, subq.c.name)
.bind(db))
Recursion
Common Table Expressions allow us to, effectively, create our own temporary tables for the duration of a
query - they're largely a convenience to help us make more readable SQL. Using the WITH RECURSIVE
modifier, however, it's possible for us to create recursive queries. This is enormously advantageous for
working with tree and graph-structured data - imagine retrieving all of the relations of a graph node to
a given depth, for example.
Find the upward recommendation chain for member ID 27
Find the upward recommendation chain for member ID 27: that is, the member who recommended them, and the
member who recommended that member, and so on. Return member ID, first name, and surname. Order by
descending member id.
WITH RECURSIVE recommenders(recommender) as (
SELECT recommendedby FROM members WHERE memid = 27
UNION ALL
SELECT mems.recommendedby
FROM recommenders recs
INNER JOIN members AS mems ON mems.memid = recs.recommender
)
SELECT recs.recommender, mems.firstname, mems.surname
FROM recommenders AS recs
INNER JOIN members AS mems ON recs.recommender = mems.memid
ORDER By memid DESC;
# Base-case of recursive CTE. Get member recommender where memid=27.
base = (Member
.select(Member.recommendedby)
.where(Member.memid == 27)
.cte('recommenders', recursive=True, columns=('recommender',)))
# Recursive term of CTE. Get recommender of previous recommender.
MA = Member.alias()
recursive = (MA
.select(MA.recommendedby)
.join(base, on=(MA.memid == base.c.recommender)))
# Combine the base-case with the recursive term.
cte = base.union_all(recursive)
# Select from the recursive CTE, joining on member to get name info.
query = (cte
.select_from(cte.c.recommender, Member.firstname, Member.surname)
.join(Member, on=(cte.c.recommender == Member.memid))
.order_by(Member.memid.desc()))
Query Builder
Peewee's high-level Model and Field APIs are built upon lower-level Table and Column counterparts. While
these lower-level APIs are not documented in as much detail as their high-level counterparts, this
document will present an overview with examples that should hopefully allow you to experiment.
We'll use the following schema:
CREATE TABLE "person" (
"id" INTEGER NOT NULL PRIMARY KEY,
"first" TEXT NOT NULL,
"last" TEXT NOT NULL);
CREATE TABLE "note" (
"id" INTEGER NOT NULL PRIMARY KEY,
"person_id" INTEGER NOT NULL,
"content" TEXT NOT NULL,
"timestamp" DATETIME NOT NULL,
FOREIGN KEY ("person_id") REFERENCES "person" ("id"));
CREATE TABLE "reminder" (
"id" INTEGER NOT NULL PRIMARY KEY,
"note_id" INTEGER NOT NULL,
"alarm" DATETIME NOT NULL,
FOREIGN KEY ("note_id") REFERENCES "note" ("id"));
Declaring tables
There are two ways we can declare Table objects for working with these tables:
# Explicitly declare columns
Person = Table('person', ('id', 'first', 'last'))
Note = Table('note', ('id', 'person_id', 'content', 'timestamp'))
# Do not declare columns, they will be accessed using magic ".c" attribute
Reminder = Table('reminder')
Typically we will want to bind() our tables to a database. This saves us having to pass the database
explicitly every time we wish to execute a query on the table:
db = SqliteDatabase('my_app.db')
Person = Person.bind(db)
Note = Note.bind(db)
Reminder = Reminder.bind(db)
Select queries
To select the first three notes and print their content, we can write:
query = Note.select().order_by(Note.timestamp).limit(3)
for note_dict in query:
print(note_dict['content'])
NOTE:
By default, rows will be returned as dictionaries. You can use the tuples(), namedtuples() or
objects() methods to specify a different container for the row data, if you wish.
Because we didn't specify any columns, all the columns we defined in the note's Table constructor will be
selected. This won't work for Reminder, as we didn't specify any columns at all.
To select all notes published in 2018 along with the name of the creator, we will use join(). We'll also
request that rows be returned as namedtuple objects:
query = (Note
.select(Note.content, Note.timestamp, Person.first, Person.last)
.join(Person, on=(Note.person_id == Person.id))
.where(Note.timestamp >= datetime.date(2018, 1, 1))
.order_by(Note.timestamp)
.namedtuples())
for row in query:
print(row.timestamp, '-', row.content, '-', row.first, row.last)
Let's query for the most prolific people, that is, get the people who have created the most notes. This
introduces calling a SQL function (COUNT), which is accomplished using the fn object:
name = Person.first.concat(' ').concat(Person.last)
query = (Person
.select(name.alias('name'), fn.COUNT(Note.id).alias('count'))
.join(Note, JOIN.LEFT_OUTER, on=(Note.person_id == Person.id))
.group_by(name)
.order_by(fn.COUNT(Note.id).desc()))
for row in query:
print(row['name'], row['count'])
There are a couple things to note in the above query:
• We store an expression in a variable (name), then use it in the query.
• We call SQL functions using fn.<function>(...) passing arguments as if it were a normal Python
function.
• The alias() method is used to specify the name used for a column or calculation.
As a more complex example, we'll generate a list of all people and the contents and timestamp of their
most recently-published note. To do this, we will end up using the Note table twice in different contexts
within the same query, which will require us to use a table alias.
# Start with the query that calculates the timestamp of the most recent
# note for each person.
NA = Note.alias('na')
max_note = (NA
.select(NA.person_id, fn.MAX(NA.timestamp).alias('max_ts'))
.group_by(NA.person_id)
.alias('max_note'))
# Now we'll select from the note table, joining on both the subquery and
# on the person table to construct the result set.
query = (Note
.select(Note.content, Note.timestamp, Person.first, Person.last)
.join(max_note, on=((max_note.c.person_id == Note.person_id) &
(max_note.c.max_ts == Note.timestamp)))
.join(Person, on=(Note.person_id == Person.id))
.order_by(Person.first, Person.last))
for row in query.namedtuples():
print(row.first, row.last, ':', row.timestamp, '-', row.content)
In the join predicate for the join on the max_note subquery, we can reference columns in the subquery
using the magical ".c" attribute. So, max_note.c.max_ts is translated into "the max_ts column value from
the max_note subquery".
We can also use the ".c" magic attribute to access columns on tables that do not explicitly define their
columns, like we did with the Reminder table. Here's a simple query to get all reminders for today,
along with their associated note content:
today = datetime.date.today()
tomorrow = today + datetime.timedelta(days=1)
query = (Reminder
.select(Reminder.c.alarm, Note.content)
.join(Note, on=(Reminder.c.note_id == Note.id))
.where(Reminder.c.alarm.between(today, tomorrow))
.order_by(Reminder.c.alarm))
for row in query:
print(row['alarm'], row['content'])
NOTE:
The ".c" attribute will not work on tables that explicitly define their columns, to prevent confusion.
Insert queries
Inserting data is straightforward. We can specify data to insert() in two different ways (in both cases,
the ID of the new row is returned):
# Using keyword arguments:
zaizee_id = Person.insert(first='zaizee', last='cat').execute()
# Using column: value mappings:
Note.insert({
Note.person_id: zaizee_id,
Note.content: 'meeeeowwww',
Note.timestamp: datetime.datetime.now()}).execute()
It is easy to bulk-insert data, just pass in either:
• A list of dictionaries (all must have the same keys/columns).
• A list of tuples, if the columns are specified explicitly.
Examples:
people = [
{'first': 'Bob', 'last': 'Foo'},
{'first': 'Herb', 'last': 'Bar'},
{'first': 'Nuggie', 'last': 'Bar'}]
# Inserting multiple rows returns the ID of the last-inserted row.
last_id = Person.insert(people).execute()
# We can also specify row tuples, so long as we tell Peewee which
# columns the tuple values correspond to:
people = [
('Bob', 'Foo'),
('Herb', 'Bar'),
('Nuggie', 'Bar')]
Person.insert(people, columns=[Person.first, Person.last]).execute()
Update queries
update() queries accept either keyword arguments or a dictionary mapping column to value, just like
insert().
Examples:
# "Bob" changed his last name from "Foo" to "Baze".
nrows = (Person
.update(last='Baze')
.where((Person.first == 'Bob') &
(Person.last == 'Foo'))
.execute())
# Use dictionary mapping column to value.
nrows = (Person
.update({Person.last: 'Baze'})
.where((Person.first == 'Bob') &
(Person.last == 'Foo'))
.execute())
You can also use expressions as the value to perform an atomic update. Imagine we have a PageView table
and we need to atomically increment the page-view count for some URL:
# Do an atomic update:
(PageView
.update({PageView.count: PageView.count + 1})
.where(PageView.url == some_url)
.execute())
Delete queries
delete() queries are simplest of all, as they do not accept any arguments:
# Delete all notes created before 2018, returning number deleted.
n = Note.delete().where(Note.timestamp < datetime.date(2018, 1, 1)).execute()
Because DELETE (and UPDATE) queries do not support joins, we can use subqueries to delete rows based on
values in related tables. For example, here is how you would delete all notes by anyone whose last name
is "Foo":
# Get the id of all people whose last name is "Foo".
foo_people = Person.select(Person.id).where(Person.last == 'Foo')
# Delete all notes by any person whose ID is in the previous query.
Note.delete().where(Note.person_id.in_(foo_people)).execute()
Query Objects
One of the fundamental limitations of the abstractions provided by Peewee 2.x was the absence of a class
that represented a structured query with no relation to a given model class.
An example of this might be computing aggregate values over a subquery. For example, the count() method,
which returns the count of rows in an arbitrary query, is implemented by wrapping the query:
SELECT COUNT(1) FROM (...)
To accomplish this with Peewee, the implementation is written in this way:
def count(query):
# Select([source1, ... sourcen], [column1, ...columnn])
wrapped = Select(from_list=[query], columns=[fn.COUNT(SQL('1'))])
curs = wrapped.tuples().execute(db)
return curs[0][0] # Return first column from first row of result.
We can actually express this more concisely using the scalar() method, which is suitable for returning
values from aggregate queries:
def count(query):
wrapped = Select(from_list=[query], columns=[fn.COUNT(SQL('1'))])
return wrapped.scalar(db)
The query_examples document has a more complex example, in which we write a query for a facility with the
highest number of available slots booked:
The SQL we wish to express is:
SELECT facid, total FROM (
SELECT facid, SUM(slots) AS total,
rank() OVER (order by SUM(slots) DESC) AS rank
FROM bookings
GROUP BY facid
) AS ranked
WHERE rank = 1
We can express this fairly elegantly by using a plain Select for the outer query:
# Store rank expression in variable for readability.
rank_expr = fn.rank().over(order_by=[fn.SUM(Booking.slots).desc()])
subq = (Booking
.select(Booking.facility, fn.SUM(Booking.slots).alias('total'),
rank_expr.alias('rank'))
.group_by(Booking.facility))
# Use a plain "Select" to create outer query.
query = (Select(columns=[subq.c.facid, subq.c.total])
.from_(subq)
.where(subq.c.rank == 1)
.tuples())
# Iterate over the resulting facility ID(s) and total(s):
for facid, total in query.execute(db):
print(facid, total)
For another example, let's create a recursive common table expression to calculate the first 10 fibonacci
numbers:
base = Select(columns=(
Value(1).alias('n'),
Value(0).alias('fib_n'),
Value(1).alias('next_fib_n'))).cte('fibonacci', recursive=True)
n = (base.c.n + 1).alias('n')
recursive_term = Select(columns=(
n,
base.c.next_fib_n,
base.c.fib_n + base.c.next_fib_n)).from_(base).where(n < 10)
fibonacci = base.union_all(recursive_term)
query = fibonacci.select_from(fibonacci.c.n, fibonacci.c.fib_n)
results = list(query.execute(db))
# Generates the following result list:
[{'fib_n': 0, 'n': 1},
{'fib_n': 1, 'n': 2},
{'fib_n': 1, 'n': 3},
{'fib_n': 2, 'n': 4},
{'fib_n': 3, 'n': 5},
{'fib_n': 5, 'n': 6},
{'fib_n': 8, 'n': 7},
{'fib_n': 13, 'n': 8},
{'fib_n': 21, 'n': 9},
{'fib_n': 34, 'n': 10}]
More
For a description of the various classes used to describe a SQL AST, see the query builder API
documentation.
If you're interested in learning more, you can also check out the project source code.
Hacks
Collected hacks using peewee. Have a cool hack you'd like to share? Open an issue on GitHub or contact
me.
Optimistic Locking
Optimistic locking is useful in situations where you might ordinarily use a SELECT FOR UPDATE (or in
SQLite, BEGIN IMMEDIATE). For example, you might fetch a user record from the database, make some
modifications, then save the modified user record. Typically this scenario would require us to lock the
user record for the duration of the transaction, from the moment we select it, to the moment we save our
changes.
In optimistic locking, on the other hand, we do not acquire any lock and instead rely on an internal
version column in the row we're modifying. At read time, we see what version the row is currently at, and
on save, we ensure that the update takes place only if the version is the same as the one we initially
read. If the version is higher, then some other process must have snuck in and changed the row -- to save
our modified version could result in the loss of important changes.
It's quite simple to implement optimistic locking in Peewee, here is a base class that you can use as a
starting point:
from peewee import *
class BaseVersionedModel(Model):
version = IntegerField(default=1, index=True)
def save_optimistic(self):
if not self.id:
# This is a new record, so the default logic is to perform an
# INSERT. Ideally your model would also have a unique
# constraint that made it impossible for two INSERTs to happen
# at the same time.
return self.save()
# Update any data that has changed and bump the version counter.
field_data = dict(self._data)
current_version = field_data.pop('version', 1)
field_data = self._prune_fields(field_data, self.dirty_fields)
if not field_data:
raise ValueError('No changes have been made.')
ModelClass = type(self)
field_data['version'] = ModelClass.version + 1 # Atomic increment.
query = ModelClass.update(**field_data).where(
(ModelClass.version == current_version) &
(ModelClass.id == self.id))
if query.execute() == 0:
# No rows were updated, indicating another process has saved
# a new version. How you handle this situation is up to you,
# but for simplicity I'm just raising an exception.
raise ConflictDetectedException()
else:
# Increment local version to match what is now in the db.
self.version += 1
return True
Here's an example of how this works. Let's assume we have the following model definition. Note that
there's a unique constraint on the username -- this is important as it provides a way to prevent
double-inserts.
class User(BaseVersionedModel):
username = CharField(unique=True)
favorite_animal = CharField()
Example:
>>> u = User(username='charlie', favorite_animal='cat')
>>> u.save_optimistic()
True
>>> u.version
1
>>> u.save_optimistic()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "x.py", line 18, in save_optimistic
raise ValueError('No changes have been made.')
ValueError: No changes have been made.
>>> u.favorite_animal = 'kitten'
>>> u.save_optimistic()
True
# Simulate a separate thread coming in and updating the model.
>>> u2 = User.get(User.username == 'charlie')
>>> u2.favorite_animal = 'macaw'
>>> u2.save_optimistic()
True
# Now, attempt to change and re-save the original instance:
>>> u.favorite_animal = 'little parrot'
>>> u.save_optimistic()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "x.py", line 30, in save_optimistic
raise ConflictDetectedException()
ConflictDetectedException: current version is out of sync
Top object per group
These examples describe several ways to query the single top item per group. For a thorough discuss of
various techniques, check out my blog post Querying the top item by group with Peewee ORM. If you are
interested in the more general problem of querying the top N items, see the section below Top N objects
per group.
In these examples we will use the User and Tweet models to find each user and their most-recent tweet.
The most efficient method I found in my testing uses the MAX() aggregate function.
We will perform the aggregation in a non-correlated subquery, so we can be confident this method will be
performant. The idea is that we will select the posts, grouped by their author, whose timestamp is equal
to the max observed timestamp for that user.
# When referencing a table multiple times, we'll call Model.alias() to create
# a secondary reference to the table.
TweetAlias = Tweet.alias()
# Create a subquery that will calculate the maximum Tweet create_date for each
# user.
subquery = (TweetAlias
.select(
TweetAlias.user,
fn.MAX(TweetAlias.create_date).alias('max_ts'))
.group_by(TweetAlias.user)
.alias('tweet_max_subquery'))
# Query for tweets and join using the subquery to match the tweet's user
# and create_date.
query = (Tweet
.select(Tweet, User)
.join(User)
.switch(Tweet)
.join(subquery, on=(
(Tweet.create_date == subquery.c.max_ts) &
(Tweet.user == subquery.c.user_id))))
SQLite and MySQL are a bit more lax and permit grouping by a subset of the columns that are selected.
This means we can do away with the subquery and express it quite concisely:
query = (Tweet
.select(Tweet, User)
.join(User)
.group_by(Tweet.user)
.having(Tweet.create_date == fn.MAX(Tweet.create_date)))
Top N objects per group
These examples describe several ways to query the top N items per group reasonably efficiently. For a
thorough discussion of various techniques, check out my blog post Querying the top N objects per group
with Peewee ORM.
In these examples we will use the User and Tweet models to find each user and their three most-recent
tweets.
Postgres lateral joins
Lateral joins are a neat Postgres feature that allow reasonably efficient correlated subqueries. They are
often described as SQL for each loops.
The desired SQL is:
SELECT * FROM
(SELECT t2.id, t2.username FROM user AS t2) AS uq
LEFT JOIN LATERAL
(SELECT t2.message, t2.create_date
FROM tweet AS t2
WHERE (t2.user_id = uq.id)
ORDER BY t2.create_date DESC LIMIT 3)
AS pq ON true
To accomplish this with peewee we'll need to express the lateral join as a Clause, which gives us greater
flexibility than the join() method.
# We'll reference `Tweet` twice, so keep an alias handy.
TweetAlias = Tweet.alias()
# The "outer loop" will be iterating over the users whose
# tweets we are trying to find.
user_query = User.select(User.id, User.username).alias('uq')
# The inner loop will select tweets and is correlated to the
# outer loop via the WHERE clause. Note that we are using a
# LIMIT clause.
tweet_query = (TweetAlias
.select(TweetAlias.message, TweetAlias.create_date)
.where(TweetAlias.user == user_query.c.id)
.order_by(TweetAlias.create_date.desc())
.limit(3)
.alias('pq'))
# Now we join the outer and inner queries using the LEFT LATERAL
# JOIN. The join predicate is *ON TRUE*, since we're effectively
# joining in the tweet subquery's WHERE clause.
join_clause = NodeList((
user_query,
SQL('LEFT JOIN LATERAL'),
tweet_query,
SQL('ON %s', [True])))
# Finally, we'll wrap these up and SELECT from the result.
query = (Tweet
.select(user_query.c.username, tweet_query.c.message,
tweet_query.c.create_date)
.from_(join_clause))
Window functions
Window functions, which are supported by peewee, provide scalable, efficient performance.
The desired SQL is:
SELECT subq.message, subq.username
FROM (
SELECT
t2.message,
t3.username,
RANK() OVER (
PARTITION BY t2.user_id
ORDER BY t2.create_date DESC
) AS rnk
FROM tweet AS t2
INNER JOIN user AS t3 ON (t2.user_id = t3.id)
) AS subq
WHERE (subq.rnk <= 3)
To accomplish this with peewee, we will wrap the ranked Tweets in an outer query that performs the
filtering.
TweetAlias = Tweet.alias()
# The subquery will select the relevant data from the Tweet and
# User table, as well as ranking the tweets by user from newest
# to oldest.
subquery = (TweetAlias
.select(
TweetAlias.message,
User.username,
fn.RANK().over(
partition_by=[TweetAlias.user],
order_by=[TweetAlias.create_date.desc()]).alias('rnk'))
.join(User, on=(TweetAlias.user == User.id))
.alias('subq'))
# Since we can't filter on the rank, we are wrapping it in a query
# and performing the filtering in the outer query.
query = (Tweet
.select(subquery.c.message, subquery.c.username)
.from_(subquery)
.where(subquery.c.rnk <= 3))
Other methods
If you're not using Postgres, then unfortunately you're left with options that exhibit less-than-ideal
performance. For a more complete overview of common methods, check out this blog post. Below I will
summarize the approaches and the corresponding SQL.
Using COUNT, we can get all tweets where there exist less than N tweets with more recent timestamps:
TweetAlias = Tweet.alias()
# Create a correlated subquery that calculates the number of
# tweets with a higher (newer) timestamp than the tweet we're
# looking at in the outer query.
subquery = (TweetAlias
.select(fn.COUNT(TweetAlias.id))
.where(
(TweetAlias.create_date >= Tweet.create_date) &
(TweetAlias.user == Tweet.user)))
# Wrap the subquery and filter on the count.
query = (Tweet
.select(Tweet, User)
.join(User)
.where(subquery <= 3))
We can achieve similar results by doing a self-join and performing the filtering in the HAVING clause:
TweetAlias = Tweet.alias()
# Use a self-join and join predicates to count the number of
# newer tweets.
query = (Tweet
.select(Tweet.id, Tweet.message, Tweet.user, User.username)
.join(User)
.switch(Tweet)
.join(TweetAlias, on=(
(TweetAlias.user == Tweet.user) &
(TweetAlias.create_date >= Tweet.create_date)))
.group_by(Tweet.id, Tweet.content, Tweet.user, User.username)
.having(fn.COUNT(Tweet.id) <= 3))
The last example uses a LIMIT clause in a correlated subquery.
TweetAlias = Tweet.alias()
# The subquery here will calculate, for the user who created the
# tweet in the outer loop, the three newest tweets. The expression
# will evaluate to `True` if the outer-loop tweet is in the set of
# tweets represented by the inner query.
query = (Tweet
.select(Tweet, User)
.join(User)
.where(Tweet.id << (
TweetAlias
.select(TweetAlias.id)
.where(TweetAlias.user == Tweet.user)
.order_by(TweetAlias.create_date.desc())
.limit(3))))
Writing custom functions with SQLite
SQLite is very easy to extend with custom functions written in Python, that are then callable from your
SQL statements. By using the SqliteExtDatabase and the func() decorator, you can very easily define your
own functions.
Here is an example function that generates a hashed version of a user-supplied password. We can also use
this to implement login functionality for matching a user and password.
from hashlib import sha1
from random import random
from playhouse.sqlite_ext import SqliteExtDatabase
db = SqliteExtDatabase('my-blog.db')
def get_hexdigest(salt, raw_password):
data = salt + raw_password
return sha1(data.encode('utf8')).hexdigest()
@db.func()
def make_password(raw_password):
salt = get_hexdigest(str(random()), str(random()))[:5]
hsh = get_hexdigest(salt, raw_password)
return '%s$%s' % (salt, hsh)
@db.func()
def check_password(raw_password, enc_password):
salt, hsh = enc_password.split('$', 1)
return hsh == get_hexdigest(salt, raw_password)
Here is how you can use the function to add a new user, storing a hashed password:
query = User.insert(
username='charlie',
password=fn.make_password('testing')).execute()
If we retrieve the user from the database, the password that's stored is hashed and salted:
>>> user = User.get(User.username == 'charlie')
>>> print user.password
b76fa$88be1adcde66a1ac16054bc17c8a297523170949
To implement login-type functionality, you could write something like this:
def login(username, password):
try:
return (User
.select()
.where(
(User.username == username) &
(fn.check_password(password, User.password) == True))
.get())
except User.DoesNotExist:
# Incorrect username and/or password.
return False
Changes in 3.0
This document describes changes to be aware of when switching from 2.x to 3.x.
Backwards-incompatible
I tried to keep changes backwards-compatible as much as possible. In some places, APIs that have changed
will trigger a DeprecationWarning.
Database
• get_conn() has changed to Database.connection()
• get_cursor() has changed to Database.cursor()
• execution_context() is replaced by simply using the database instance as a context-manager.
• For a connection context without a transaction, use Database.connection_context().
• Database.create_tables() and Database.drop_tables(), as well as Model.create_table() and
Model.drop_table() all default to safe=True (create_table will create if not exists, drop_table will
drop if exists).
• connect_kwargs attribute has been renamed to connect_params
• initialization parameter for custom field-type definitions has changed from fields to field_types.
Model Meta options
• db_table has changed to table_name
• db_table_func has changed to table_function
• order_by has been removed (used for specifying a default ordering to be applied to SELECT queries).
• validate_backrefs has been removed. Back-references are no longer validated.
Models
• BaseModel has been renamed to ModelBase
• Accessing raw model data is now done using __data__ instead of _data
Fields
• db_column has changed to column_name
• db_field class attribute changed to field_type (used if you are implementing custom field subclasses)
• model_class attribute has changed to model
• PrimaryKeyField has been renamed to AutoField
• ForeignKeyField constructor has the following changes:
• rel_model has changed to model
• to_field has changed to field
• related_name has changed to backref
• ManyToManyField is now included in the main peewee.py module
• Removed the extension fields PasswordField, PickledField and AESEncryptedField.
Querying
The C extension that contained implementations of the query result wrappers has been removed.
Additionally, Select.aggregate_rows() has been removed. This helper was used to de-duplicate left-join
queries to give the appearance of efficiency when iterating a model and its relations. In practice, the
complexity of the code and its somewhat limited usefulness convinced me to scrap it. You can instead use
prefetch() to achieve the same result.
• Select query attribute _select has changed to _returning
• The naive() method is now objects(), which defaults to using the model class as the constructor, but
accepts any callable to use as an alternate constructor.
• The annotate() query method is no longer supported.
The Case() helper has moved from the playhouse.shortcuts module into the main peewee module.
The cast() method is no longer a function, but instead is a method on all column-like objects.
The InsertQuery.return_id_list() method has been replaced by a more general pattern of using
_WriteQuery.returning().
The InsertQuery.upsert() method has been replaced by the more general and flexible Insert.on_conflict()
method.
When using prefetch(), the collected instances will be stored in the same attribute as the foreign-key's
backref. Previously, you would access joined instances using (backref)_prefetch.
The SQL object, used to create a composable a SQL string, now expects the second parameter to be a
list/tuple of parameters.
Removed Extensions
The following extensions are no longer included in the playhouse:
• berkeleydb
• csv_utils
• djpeewee
• gfk
• kv
• pskel
• read_slave
SQLite Extension
The SQLite extension module's VirtualModel class accepts slightly different Meta options:
• arguments - used to specify arbitrary arguments appended after any columns being defined on the virtual
table. Should be a list of strings.
• extension_module (unchanged)
• options (replaces extension_options) - arbitrary options for the virtual table that appear after
columns and arguments.
• prefix_arguments - a list of strings that should appear before any arguments or columns in the virtual
table declaration.
So, when declaring a model for a virtual table, it will be constructed roughly like this:
CREATE VIRTUAL TABLE "table name" USING extension_module (
prefix arguments,
field definitions,
arguments,
options)
Postgresql Extension
The PostgresqlExtDatabase no longer registers the hstore extension by default. To use the hstore
extension in 3.0 and onwards, pass register_hstore=True when initializing the database object.
Signals Extension
The post_init signal has been removed.
New stuff
The query-builder has been rewritten from the ground-up to be more flexible and powerful. There is now a
generic, lower-level API for constructing queries.
SQLite
Many SQLite-specific features have been moved from the playhouse.sqlite_ext module into peewee, such as:
• User-defined functions, aggregates, collations, and table-functions.
• Loading extensions.
• Specifying pragmas.
See the "Using SQLite" section and "SQLite extensions" documents for more details.
SQLite Extension
The virtual-table implementation from sqlite-vtfunc has been folded into the peewee codebase.
• Support for SQLite online backup API.
• Murmurhash implementation has been corrected.
• Couple small quirks in the BM25 ranking code have been addressed.
• Numerous user-defined functions for hashing and ranking are now included.
• BloomFilter implementation.
• Incremental Blob I/O support.
• Support for update, commit and rollback hooks.
• LSMTable implementation to support the lsm1 extension.
NOTE
If you find any bugs, odd behavior, or have an idea for a new feature please don't hesitate to open an
issue on GitHub or contact me.
• genindex
• modindex
• search
AUTHOR
charles leifer
COPYRIGHT
charles leifer