Provided by: libdbix-class-perl_0.082843-1_all 
NAME
DBIx::Class::Manual::FAQ - Frequently Asked Questions (in theory)
DESCRIPTION
This document is intended as an anti-map of the documentation. If you know what you want
to do, but not how to do it in DBIx::Class, then look here. It does not contain much code
or examples, it just gives explanations and pointers to the correct pieces of
documentation to read.
FAQs
How Do I:
Getting started
.. create a database to use?
First, choose a database. For testing/experimenting, we recommend DBD::SQLite, which
is a self-contained small database (i.e. all you need to do is to install DBD::SQLite
from CPAN, and it works).
Next, spend some time defining which data you need to store, and how it relates to the
other data you have. For some help on normalisation, go to
<http://b62.tripod.com/doc/dbbase.htm>.
Now, decide whether you want to have the database itself be the definitive source of
information about the data layout, or your DBIx::Class schema. If it's the former,
look up the documentation for your database, eg.
<http://sqlite.org/lang_createtable.html>, on how to create tables, and start creating
them. For a nice universal interface to your database, you can try DBI::Shell. If you
decided on the latter choice, read the FAQ on setting up your classes manually, and
the one on creating tables from your schema.
.. use DBIx::Class with Catalyst?
Install Catalyst::Model::DBIC::Schema from CPAN. See its documentation, or below, for
further details.
.. set up my DBIx::Class classes automatically from my database?
Install DBIx::Class::Schema::Loader from CPAN, and read its documentation.
.. set up my DBIx::Class classes manually?
Look at the DBIx::Class::Manual::Example and come back here if you get lost.
.. create my database tables from my DBIx::Class schema?
Create your classes manually, as above. Write a script that calls "deploy" in
DBIx::Class::Schema. See there for details, or the DBIx::Class::Manual::Cookbook.
.. store/retrieve Unicode data in my database?
Make sure you database supports Unicode and set the connect attributes appropriately -
see "Using Unicode" in DBIx::Class::Manual::Cookbook
.. connect to my database?
Once you have created all the appropriate table/source classes, and an overall Schema
class, you can start using them in an application. To do this, you need to create a
central Schema object, which is used to access all the data in the various tables. See
"connect" in DBIx::Class::Schema for details. The actual connection does not happen
until you actually request data, so don't be alarmed if the error from incorrect
connection details happens a lot later.
.. use DBIx::Class across multiple databases?
If your database server allows you to run queries across multiple databases at once,
then so can DBIx::Class. All you need to do is make sure you write the database name
as part of the table call. Eg:
__PACKAGE__->table('mydb.mytablename');
And load all the Result classes for both / all databases by calling "load_namespaces"
in DBIx::Class::Schema.
.. use DBIx::Class across PostgreSQL/DB2/Oracle schemas?
Add the name of the schema to the table name, when invoking table, and make sure the
user you are about to connect as has permissions to read/write all the schemas/tables
as necessary.
Relationships
.. tell DBIx::Class about relationships between my tables?
There are a variety of relationship types that come pre-defined for you to use. These
are all listed in DBIx::Class::Relationship. If you need a non-standard type, or more
information, look in DBIx::Class::Relationship::Base.
.. define a one-to-many relationship?
This is called a "has_many" relationship on the one side, and a "belongs_to"
relationship on the many side. Currently these need to be set up individually on each
side. See DBIx::Class::Relationship for details.
.. define a relationship where this table contains another table's primary key? (foreign
key)
Create a "belongs_to" relationship for the field containing the foreign key. See
"belongs_to" in DBIx::Class::Relationship.
.. define a foreign key relationship where the key field may contain NULL?
Just create a "belongs_to" relationship, as above. If the column is NULL then the
inflation to the foreign object will not happen. This has a side effect of not always
fetching all the relevant data, if you use a nullable foreign-key relationship in a
JOIN, then you probably want to set the "join_type" to "left".
.. define a relationship where the key consists of more than one column?
Instead of supplying a single column name, all relationship types also allow you to
supply a hashref containing the condition across which the tables are to be joined.
The condition may contain as many fields as you like. See
DBIx::Class::Relationship::Base.
.. define a relationship bridge across an intermediate table? (many-to-many)
The term 'relationship' is used loosely with many_to_many as it is not considered a
relationship in the fullest sense. For more info, read the documentation on
"many_to_many" in DBIx::Class::Relationship.
.. stop DBIx::Class from attempting to cascade deletes on my has_many and might_have
relationships?
By default, DBIx::Class cascades deletes and updates across "has_many" and
"might_have" relationships. You can disable this behaviour on a per-relationship basis
by supplying "cascade_delete => 0" in the relationship attributes.
The cascaded operations are performed after the requested delete or update, so if your
database has a constraint on the relationship, it will have deleted/updated the
related records or raised an exception before DBIx::Class gets to perform the cascaded
operation.
See DBIx::Class::Relationship.
.. use a relationship?
Use its name. An accessor is created using the name. See examples in "USING
RELATIONSHIPS" in DBIx::Class::Manual::Cookbook.
Searching
.. search for data?
Create a $schema object, as mentioned above in ".. connect to my database?". Find the
ResultSet that you want to search in, by calling "$schema->resultset('MySource')" and
call "search" on it. See "search" in DBIx::Class::ResultSet.
.. search using database functions?
Supplying something like:
->search({'mydatefield' => 'now()'})
to search, will probably not do what you expect. It will quote the text "now()",
instead of trying to call the function. To provide literal, unquoted text you need to
pass in a scalar reference, like so:
->search({'mydatefield' => \'now()'})
.. sort the results of my search?
Supply a list of columns you want to sort by to the "order_by" attribute. See
"order_by" in DBIx::Class::ResultSet.
.. sort my results based on fields I've aliased using "as"?
You didn't alias anything, since as has nothing to do with the produced SQL. See
"select" in DBIx::Class::ResultSet for details.
.. group the results of my search?
Supply a list of columns you want to group on, to the "group_by" attribute, see
"group_by" in DBIx::Class::ResultSet.
.. group my results based on fields I've aliased using "as"?
You don't. See the explanation on ordering by an alias above.
.. filter the results of my search?
The first argument to "search" is a hashref of accessor names and values to filter
them by, for example:
->search({'created_time' => { '>=', '2006-06-01 00:00:00' } })
Note that to use a function here you need to make it a scalar reference:
->search({'created_time' => { '>=', \'yesterday()' } })
.. search in several tables simultaneously?
To search in two related tables, you first need to set up appropriate relationships
between their respective classes. When searching you then supply the name of the
relationship to the "join" attribute in your search, for example when searching in the
Books table for all the books by the author "Fred Bloggs":
->search({'authors.name' => 'Fred Bloggs'}, { join => 'authors' })
The type of join created in your SQL depends on the type of relationship between the
two tables, see DBIx::Class::Relationship for the join used by each relationship.
.. create joins with conditions other than column equality?
Currently, DBIx::Class can only create join conditions using equality, so you're
probably better off creating a "view" in your database, and using that as your source.
A "view" is a stored SQL query, which can be accessed similarly to a table, see your
database documentation for details.
.. search with an SQL function on the left hand side?
To use an SQL function on the left hand side of a comparison you currently need to
resort to literal SQL:
->search( \[ 'YEAR(date_of_birth) = ?', 1979 ] );
.. find more help on constructing searches?
Behind the scenes, DBIx::Class uses SQL::Abstract::Classic to help construct its SQL
searches. So if you fail to find help in the DBIx::Class::Manual::Cookbook, try
looking in the SQL::Abstract::Classic documentation.
.. make searches in Oracle (10gR2 and newer) case-insensitive?
To make Oracle behave like most RDBMS use on_connect_do to issue alter session
statements on database connection establishment:
->on_connect_do("ALTER SESSION SET NLS_COMP = 'LINGUISTIC'");
->on_connect_do("ALTER SESSION SET NLS_SORT = '<NLS>_CI'");
e.g.
->on_connect_do("ALTER SESSION SET NLS_SORT = 'BINARY_CI'");
->on_connect_do("ALTER SESSION SET NLS_SORT = 'GERMAN_CI'");
.. format a DateTime object for searching?
search and find do not take DBIx::Class::InflateColumn into account, and so your
DateTime object will not be correctly deflated into a format your RDBMS expects.
The datetime_parser method on your storage object can be used to return the object
that would normally do this, so it's easy to do it manually:
my $dtf = $schema->storage->datetime_parser;
my $rs = $schema->resultset('users')->search(
{
signup_date => {
-between => [
$dtf->format_datetime($dt_start),
$dtf->format_datetime($dt_end),
],
}
},
);
With in a Result Class method, you can get this from the "result_source".
my $dtf = $self->result_source->storage->datetime_parser;
This kludge is necessary only for conditions passed to search and "find" in
DBIx::Class::ResultSet, whereas create and "update" in DBIx::Class::Row (but not
"update" in DBIx::Class::ResultSet) are DBIx::Class::InflateColumn-aware and will do
the right thing when supplied an inflated DateTime object.
Fetching data
.. fetch as much data as possible in as few select calls as possible?
See the prefetch examples in the Cookbook.
.. fetch a whole column of data instead of a row?
Call "get_column" on a DBIx::Class::ResultSet. This returns a
DBIx::Class::ResultSetColumn. See its documentation and the Cookbook for details.
.. fetch a formatted column?
In your table schema class, create a "private" column accessor with:
__PACKAGE__->add_columns(my_column => { accessor => '_hidden_my_column' });
Then, in the same class, implement a subroutine called "my_column" that fetches the
real value and does the formatting you want.
See the Cookbook for more details.
.. fetch a single (or topmost) row?
Use the "rows" in DBIx::Class::ResultSet and "order_by" in DBIx::Class::ResultSet
attributes to order your data and pick off a single row.
See also "Retrieve one and only one row from a resultset" in
DBIx::Class::Manual::Cookbook.
A less readable way is to ask a regular search to return 1 row, using "slice" in
DBIx::Class::ResultSet:
->search->(undef, { order_by => "id DESC" })->slice(0)
which (if supported by the database) will use LIMIT/OFFSET to hint to the database
that we really only need one row. This can result in a significant speed improvement.
The method using "single" in DBIx::Class::ResultSet mentioned in the cookbook can do
the same if you pass a "rows" attribute to the search.
.. refresh a row from storage?
Use "discard_changes" in DBIx::Class::Row.
$result->discard_changes
Discarding changes and refreshing from storage are two sides of the same coin. When
you want to discard your local changes, just re-fetch the row from storage. When you
want to get a new, fresh copy of the row, just re-fetch the row from storage.
"discard_changes" in DBIx::Class::Row does just that by re-fetching the row from
storage using the row's primary key.
.. fetch my data a "page" at a time?
Pass the "rows" and "page" attributes to your search, eg:
->search({}, { rows => 10, page => 1});
.. get a count of all rows even when paging?
Call "pager" on the paged resultset, it will return a pager object
with an API/behavior identical to that of Data::Page from late 2009 through late 2019
<https://metacpan.org/pod/release/LBROCARD/Data-Page-2.02/lib/Data/Page.pm>. Calling
"total_entries" on the pager will return the correct total.
"count" on the resultset will only return the total number in the page.
Inserting and updating data
.. insert a row with an auto incrementing primary key?
This happens automatically. After creating a result object, the primary key value
created by your database can be fetched by calling "id" (or the access of your primary
key column) on the object.
.. insert a row with a primary key that uses a sequence?
You need to create a trigger in your database that updates your primary key field from
the sequence. To help PK::Auto find the next key value, you can tell it the name of
the sequence in the "column_info" supplied with "add_columns".
->add_columns({ id => { sequence => 'mysequence', auto_nextval => 1 } });
.. insert many rows of data efficiently?
The "populate" method in DBIx::Class::ResultSet provides efficient bulk inserts.
DBIx::Class::Fixtures provides an alternative way to do this.
.. update a collection of rows at the same time?
Create a resultset using a "search", to filter the rows of data you would like to
update, then call "update" on the resultset to change all the rows at once.
.. use database functions when updating rows?
.. update a column using data from another column?
To stop the column name from being quoted, you'll need to tell DBIC that the right
hand side is an SQL identifier (it will be quoted properly if you have quoting
enabled):
->update({ somecolumn => { -ident => 'othercolumn' } })
This method will not retrieve the new value and put it in your Row object. To fetch
the new value, use the "discard_changes" method on the Row.
# will return the scalar reference:
$result->somecolumn()
# issue a select using the PK to re-fetch the row data:
$result->discard_changes();
# Now returns the correct new value:
$result->somecolumn()
To update and refresh at once, chain your calls:
$result->update({ 'somecolumn' => { -ident => 'othercolumn' } })->discard_changes;
.. store JSON/YAML in a column and have it deflate/inflate automatically?
You can use DBIx::Class::InflateColumn to accomplish YAML/JSON storage transparently.
If you want to use JSON, then in your table schema class, do the following:
use JSON;
__PACKAGE__->add_columns(qw/ ... my_column ../)
__PACKAGE__->inflate_column('my_column', {
inflate => sub { jsonToObj(shift) },
deflate => sub { objToJson(shift) },
});
For YAML, in your table schema class, do the following:
use YAML;
__PACKAGE__->add_columns(qw/ ... my_column ../)
__PACKAGE__->inflate_column('my_column', {
inflate => sub { YAML::Load(shift) },
deflate => sub { YAML::Dump(shift) },
});
This technique is an easy way to store supplemental unstructured data in a table. Be
careful not to overuse this capability, however. If you find yourself depending more
and more on some data within the inflated column, then it may be time to factor that
data out.
Custom methods in Result classes
You can add custom methods that do arbitrary things, even to unrelated tables. For
example, to provide a "$book->foo()" method which searches the cd table, you'd could add
this to Book.pm:
sub foo {
my ($self, $col_data) = @_;
return $self->result_source->schema->resultset('cd')->search($col_data);
}
And invoke that on any Book Result object like so:
my $rs = $book->foo({ title => 'Down to Earth' });
When two tables ARE related, DBIx::Class::Relationship::Base provides many methods to find
or create data in related tables for you. But if you want to write your own methods, you
can.
For example, to provide a "$book->foo()" method to manually implement what
create_related() from DBIx::Class::Relationship::Base does, you could add this to Book.pm:
sub foo {
my ($self, $rel_name, $col_data) = @_;
return $self->related_resultset($rel_name)->create($col_data);
}
Invoked like this:
my $author = $book->foo('author', { name => 'Fred' });
Misc
How do I store my own (non-db) data in my DBIx::Class objects?
You can add your own data accessors to your Result classes.
One method is to use the built in mk_group_accessors (via Class::Accessor::Grouped)
package App::Schema::Result::MyTable;
use parent 'DBIx::Class::Core';
__PACKAGE__->table('foo'); #etc
__PACKAGE__->mk_group_accessors('simple' => qw/non_column_data/); # must use simple group
And another method is to use Moose with your DBIx::Class package.
package App::Schema::Result::MyTable;
use Moose; # import Moose
use Moose::Util::TypeConstraint; # import Moose accessor type constraints
extends 'DBIx::Class::Core'; # Moose changes the way we define our parent (base) package
has 'non_column_data' => ( is => 'rw', isa => 'Str' ); # define a simple attribute
__PACKAGE__->table('foo'); # etc
With either of these methods the resulting use of the accessor would be
my $result;
# assume that somewhere in here $result will get assigned to a MyTable row
$result->non_column_data('some string'); # would set the non_column_data accessor
# some other stuff happens here
$result->update(); # would not inline the non_column_data accessor into the update
How do I use DBIx::Class objects in my TT templates?
Like normal objects, mostly. However you need to watch out for TT calling methods in
list context. When calling relationship accessors you will not get resultsets, but a
list of all the related objects.
Use the "search_rs" in DBIx::Class::ResultSet method, or the relationship accessor
methods ending with "_rs" to work around this issue.
See also "has_many" in DBIx::Class::Relationship.
See the SQL statements my code is producing?
Set the shell environment variable "DBIC_TRACE" to a true value.
For more info see DBIx::Class::Storage for details of how to turn on debugging in the
environment, pass your own filehandle to save debug to, or create your own callback.
Why didn't my search run any SQL?
DBIx::Class runs the actual SQL statement as late as possible, thus if you create a
resultset using "search" in scalar context, no query is executed. You can create
further resultset refinements by calling search again or relationship accessors. The
SQL query is only run when you ask the resultset for an actual result object.
How do I deal with tables that lack a primary key?
If your table lacks a primary key, DBIx::Class can't work out which row it should
operate on, for example to delete or update. However, a UNIQUE constraint on one or
more columns allows DBIx::Class to uniquely identify the row, so you can tell
DBIx::Class::ResultSource these columns act as a primary key, even if they don't from
the database's point of view:
$resultset->set_primary_key(@column);
How do I make my program start faster?
Look at the tips in "STARTUP SPEED" in DBIx::Class::Manual::Cookbook
How do I reduce the overhead of database queries?
You can reduce the overhead of object creation within DBIx::Class using the tips in
"Skip result object creation for faster results" in DBIx::Class::Manual::Cookbook and
"Get raw data for blindingly fast results" in DBIx::Class::Manual::Cookbook
How do I override a run time method (e.g. a relationship accessor)?
If you need access to the original accessor, then you must "wrap around" the original
method. You can do that either with Moose::Manual::MethodModifiers or
Class::Method::Modifiers. The code example works for both modules:
package Your::Schema::Group;
use Class::Method::Modifiers;
# ... declare columns ...
__PACKAGE__->has_many('group_servers', 'Your::Schema::GroupServer', 'group_id');
__PACKAGE__->many_to_many('servers', 'group_servers', 'server');
# if the server group is a "super group", then return all servers
# otherwise return only servers that belongs to the given group
around 'servers' => sub {
my $orig = shift;
my $self = shift;
return $self->$orig(@_) unless $self->is_super_group;
return $self->result_source->schema->resultset('Server')->all;
};
If you just want to override the original method, and don't care about the data from
the original accessor, then you have two options. Either use
Method::Signatures::Simple that does most of the work for you, or do it the "dirty
way".
Method::Signatures::Simple way:
package Your::Schema::Group;
use Method::Signatures::Simple;
# ... declare columns ...
__PACKAGE__->has_many('group_servers', 'Your::Schema::GroupServer', 'group_id');
__PACKAGE__->many_to_many('servers', 'group_servers', 'server');
# The method keyword automatically injects the annoying my $self = shift; for you.
method servers {
return $self->result_source->schema->resultset('Server')->search({ ... });
}
The dirty way:
package Your::Schema::Group;
use Sub::Name;
# ... declare columns ...
__PACKAGE__->has_many('group_servers', 'Your::Schema::GroupServer', 'group_id');
__PACKAGE__->many_to_many('servers', 'group_servers', 'server');
*servers = subname servers => sub {
my $self = shift;
return $self->result_source->schema->resultset('Server')->search({ ... });
};
Notes for CDBI users
Is there a way to make an object auto-stringify itself as a particular column or group of
columns (a-la cdbi Stringfy column group, or stringify_self method) ?
See "Stringification" in DBIx::Class::Manual::Cookbook
Troubleshooting
Help, I can't connect to postgresql!
If you get an error such as:
DBI connect('dbname=dbic','user',...) failed: could not connect to server:
No such file or directory Is the server running locally and accepting
connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?
Likely you have/had two copies of postgresql installed simultaneously, the second one
will use a default port of 5433, while DBD::Pg is compiled with a default port of
5432.
You can change the port setting in "postgresql.conf".
I've lost or forgotten my mysql password
Stop mysqld and restart it with the --skip-grant-tables option.
Issue the following statements in the mysql client.
UPDATE mysql.user SET Password=PASSWORD('MyNewPass') WHERE User='root';
FLUSH PRIVILEGES;
Restart mysql.
Taken from:
<http://dev.mysql.com/doc/refman/5.1/en/resetting-permissions.html>.
FURTHER QUESTIONS?
Check the list of additional DBIC resources.
COPYRIGHT AND LICENSE
This module is free software copyright by the DBIx::Class (DBIC) authors. You can
redistribute it and/or modify it under the same terms as the DBIx::Class library.