Provided by: libdbix-class-perl_0.08250-2_all 
NAME
DBIx::Class::Manual::Intro - Introduction to DBIx::Class
INTRODUCTION
You're bored with SQL, and want a native Perl interface for your database? Or you've been
doing this for a while with Class::DBI, and think there's a better way? You've come to
the right place.
THE DBIx::Class WAY
Here are a few simple tips that will help you get your bearings with DBIx::Class.
Tables become Result classes
DBIx::Class needs to know what your Table structure looks like. You do that by defining
Result classes. Result classes are defined by calling methods proxied to
DBIx::Class::ResultSource. Each Result class defines one Table, which defines the Columns
it has, along with any Relationships it has to other tables. (And oh, so much more
besides) The important thing to understand:
A Result class == Table
(most of the time, but just bear with my simplification)
It's all about the ResultSet
So, we've got some ResultSources defined. Now, we want to actually use those definitions
to help us translate the queries we need into handy perl objects!
Let's say we defined a ResultSource for an "album" table with three columns: "albumid",
"artist", and "title". Any time we want to query this table, we'll be creating a
DBIx::Class::ResultSet from its ResultSource. For example, the results of:
SELECT albumid, artist, title FROM album;
Would be retrieved by creating a ResultSet object from the album table's ResultSource,
likely by using the "search" method.
DBIx::Class doesn't limit you to creating only simple ResultSets -- if you wanted to do
something like:
SELECT title FROM album GROUP BY title;
You could easily achieve it.
The important thing to understand:
Any time you would reach for a SQL query in DBI, you are
creating a DBIx::Class::ResultSet.
Search is like "prepare"
DBIx::Class tends to wait until it absolutely must fetch information from the database.
If you are returning a ResultSet, the query won't execute until you use a method that
wants to access the data. (Such as "next", or "first")
The important thing to understand:
Setting up a ResultSet does not execute the query; retrieving
the data does.
Search results are returned as Rows
Rows of the search from the database are blessed into Result objects.
SETTING UP DBIx::Class
Let's look at how you can set and use your first native DBIx::Class tree.
First we'll see how you can set up your classes yourself. If you want them to be auto-
discovered, just skip to the next section, which shows you how to use
DBIx::Class::Schema::Loader.
Setting it up manually
First, you should create your base schema class, which inherits from DBIx::Class::Schema:
package My::Schema;
use base qw/DBIx::Class::Schema/;
In this class you load your result_source ("table", "model") classes, which we will define
later, using the load_namespaces() method:
# load My::Schema::Result::* and their resultset classes
__PACKAGE__->load_namespaces();
By default this loads all the Result (Row) classes in the My::Schema::Result:: namespace,
and also any resultset classes in the My::Schema::ResultSet:: namespace (if missing, the
resultsets are defaulted to be DBIx::Class::ResultSet objects). You can change the result
and resultset namespaces by using options to the "load_namespaces" in DBIx::Class::Schema
call.
It is also possible to do the same things manually by calling "load_classes" for the Row
classes and defining in those classes any required resultset classes.
Next, create each of the classes you want to load as specified above:
package My::Schema::Result::Album;
use base qw/DBIx::Class::Core/;
Load any additional components you may need with the load_components() method, and provide
component configuration if required. For example, if you want automatic row ordering:
__PACKAGE__->load_components(qw/ Ordered /);
__PACKAGE__->position_column('rank');
Ordered will refer to a field called 'position' unless otherwise directed. Here you are
defining the ordering field to be named 'rank'. (NOTE: Insert errors may occur if you use
the Ordered component, but have not defined a position column or have a 'position' field
in your row.)
Set the table for your class:
__PACKAGE__->table('album');
Add columns to your class:
__PACKAGE__->add_columns(qw/ albumid artist title rank /);
Each column can also be set up with its own accessor, data_type and other pieces of
information that it may be useful to have -- just pass "add_columns" a hash:
__PACKAGE__->add_columns(albumid =>
{ accessor => 'album',
data_type => 'integer',
size => 16,
is_nullable => 0,
is_auto_increment => 1,
},
artist =>
{ data_type => 'integer',
size => 16,
is_nullable => 0,
},
title =>
{ data_type => 'varchar',
size => 256,
is_nullable => 0,
},
rank =>
{ data_type => 'integer',
size => 16,
is_nullable => 0,
default_value => 0,
}
);
DBIx::Class doesn't directly use most of this data yet, but various related modules such
as HTML::FormHandler::Model::DBIC make use of it. Also it allows you to create your
database tables from your Schema, instead of the other way around. See "deploy" in
DBIx::Class::Schema for details.
See DBIx::Class::ResultSource for more details of the possible column attributes.
Accessors are created for each column automatically, so My::Schema::Result::Album will
have albumid() (or album(), when using the accessor), artist() and title() methods.
Define a primary key for your class:
__PACKAGE__->set_primary_key('albumid');
If you have a multi-column primary key, just pass a list instead:
__PACKAGE__->set_primary_key( qw/ albumid artistid / );
Define this class' relationships with other classes using either "belongs_to" to describe
a column which contains an ID of another Table, or "has_many" to make a predefined
accessor for fetching objects that contain this Table's foreign key:
# in My::Schema::Result::Artist
__PACKAGE__->has_many('albums', 'My::Schema::Result::Album', 'artist');
See DBIx::Class::Relationship for more information about the various types of available
relationships and how you can design your own.
Using DBIx::Class::Schema::Loader
This module (DBIx::Class::Schema::Loader) is an external module, and not part of the
DBIx::Class distribution. It inspects your database, and automatically creates classes for
all the tables in your schema.
The simplest way to use it is via the dbicdump script from the DBIx::Class::Schema::Loader
distribution. For example:
$ dbicdump -o dump_directory=./lib \
-o components='["InflateColumn::DateTime"]' \
MyApp::Schema dbi:mysql:mydb user pass
If you have a mixed-case database, use the "preserve_case" option, e.g.:
$ dbicdump -o dump_directory=./lib -o preserve_case=1 \
-o components='["InflateColumn::DateTime"]' \
MyApp::Schema dbi:mysql:mydb user pass
If you are using Catalyst, then you can use the helper that comes with
Catalyst::Model::DBIC::Schema:
$ script/myapp_create.pl model MyDB DBIC::Schema MyDB::Schema \
create=static moniker_map='{ foo => "FOO" }' dbi:SQLite:./myapp.db \
on_connect_do='PRAGMA foreign_keys=ON' quote_char='"'
See Catalyst::Helper::Model::DBIC::Schema for more information on this helper.
See the DBIx::Class::Schema::Loader and DBIx::Class::Schema::Loader::Base documentation
for more information on the many loader options.
Connecting
To connect to your Schema, you need to provide the connection details or a database
handle.
Via connection details
The arguments are the same as for "connect" in DBI:
my $schema = My::Schema->connect('dbi:SQLite:/home/me/myapp/my.db');
You can create as many different schema instances as you need. So if you have a second
database you want to access:
my $other_schema = My::Schema->connect( $dsn, $user, $password, $attrs );
Note that DBIx::Class::Schema does not cache connections for you. If you use multiple
connections, you need to do this manually.
To execute some SQL statements on every connect you can add them as an option in a special
fifth argument to connect:
my $another_schema = My::Schema->connect(
$dsn,
$user,
$password,
$attrs,
{ on_connect_do => \@on_connect_sql_statments }
);
See "connect_info" in DBIx::Class::Storage::DBI for more information about this and other
special "connect"-time options.
Via a database handle
The supplied coderef is expected to return a single connected database handle (e.g. a DBI
$dbh)
my $schema = My::Schema->connect (
sub { Some::DBH::Factory->connect },
\%extra_attrs,
);
Basic usage
Once you've defined the basic classes, either manually or using
DBIx::Class::Schema::Loader, you can start interacting with your database.
To access your database using your $schema object, you can fetch a "ResultSet" in
DBIx::Class::Manual::Glossary representing each of your tables by calling the "resultset"
method.
The simplest way to get a record is by primary key:
my $album = $schema->resultset('Album')->find(14);
This will run a "SELECT" with "albumid = 14" in the "WHERE" clause, and return an instance
of "My::Schema::Result::Album" that represents this row. Once you have that row, you can
access and update columns:
$album->title('Physical Graffiti');
my $title = $album->title; # $title holds 'Physical Graffiti'
If you prefer, you can use the "set_column" and "get_column" accessors instead:
$album->set_column('title', 'Presence');
$title = $album->get_column('title');
Just like with Class::DBI, you call "update" to save your changes to the database (by
executing the actual "UPDATE" statement):
$album->update;
If needed, you can throw away your local changes:
$album->discard_changes if $album->is_changed;
As you can see, "is_changed" allows you to check if there are local changes to your
object.
Adding and removing rows
To create a new record in the database, you can use the "create" method. It returns an
instance of "My::Schema::Result::Album" that can be used to access the data in the new
record:
my $new_album = $schema->resultset('Album')->create({
title => 'Wish You Were Here',
artist => 'Pink Floyd'
});
Now you can add data to the new record:
$new_album->label('Capitol');
$new_album->year('1975');
$new_album->update;
Likewise, you can remove it from the database:
$new_album->delete;
You can also remove records without retrieving them first, by calling delete directly on a
ResultSet object.
# Delete all of Falco's albums
$schema->resultset('Album')->search({ artist => 'Falco' })->delete;
Finding your objects
DBIx::Class provides a few different ways to retrieve data from your database. Here's one
example:
# Find all of Santana's albums
my $rs = $schema->resultset('Album')->search({ artist => 'Santana' });
In scalar context, as above, "search" returns a DBIx::Class::ResultSet object. It can be
used to peek at the first album returned by the database:
my $album = $rs->first;
print $album->title;
You can loop over the albums and update each one:
while (my $album = $rs->next) {
print $album->artist . ' - ' . $album->title;
$album->year(2001);
$album->update;
}
Or, you can update them all at once:
$rs->update({ year => 2001 });
In list context, the "search" method returns all of the matching rows:
# Fetch immediately all of Carlos Santana's albums
my @albums = $schema->resultset('Album')->search(
{ artist => 'Carlos Santana' }
);
foreach my $album (@albums) {
print $album->artist . ' - ' . $album->title;
}
We also provide a handy shortcut for doing a "LIKE" search:
# Find albums whose artist starts with 'Jimi'
my $rs = $schema->resultset('Album')->search_like({ artist => 'Jimi%' });
Or you can provide your own "WHERE" clause:
# Find Peter Frampton albums from the year 1986
my $where = 'artist = ? AND year = ?';
my @bind = ( 'Peter Frampton', 1986 );
my $rs = $schema->resultset('Album')->search_literal( $where, @bind );
The preferred way to generate complex queries is to provide a SQL::Abstract construct to
"search":
my $rs = $schema->resultset('Album')->search({
artist => { '!=', 'Janis Joplin' },
year => { '<' => 1980 },
albumid => { '-in' => [ 1, 14, 15, 65, 43 ] }
});
This results in something like the following "WHERE" clause:
WHERE artist != 'Janis Joplin'
AND year < 1980
AND albumid IN (1, 14, 15, 65, 43)
For more examples of complex queries, see DBIx::Class::Manual::Cookbook.
The search can also be modified by passing another hash with attributes:
my @albums = My::Schema->resultset('Album')->search(
{ artist => 'Bob Marley' },
{ rows => 2, order_by => { -desc => 'year' } }
);
@albums then holds the two most recent Bob Marley albums.
For more information on what you can do with a DBIx::Class::ResultSet, see "METHODS" in
DBIx::Class::ResultSet.
For a complete overview of the available attributes, see "ATTRIBUTES" in
DBIx::Class::ResultSet.
NOTES
The Significance and Importance of Primary Keys
The concept of a primary key in DBIx::Class warrants special discussion. The formal
definition (which somewhat resembles that of a classic RDBMS) is a unique constraint that
is least likely to change after initial row creation. However this is where the similarity
ends. Any time you call a CRUD operation on a row (e.g. delete, update, discard_changes,
etc.) DBIx::Class will use the values of of the primary key columns to populate the
"WHERE" clause necessary to accomplish the operation. This is why it is important to
declare a primary key on all your result sources even if the underlying RDBMS does not
have one. In a pinch one can always declare each row identifiable by all its columns:
__PACKAGE__->set_primary_key(__PACKAGE__->columns);
Note that DBIx::Class is smart enough to store a copy of the PK values before any row-
object changes take place, so even if you change the values of PK columns the "WHERE"
clause will remain correct.
If you elect not to declare a "primary key", DBIx::Class will behave correctly by throwing
exceptions on any row operation that relies on unique identifiable rows. If you inherited
datasets with multiple identical rows in them, you can still operate with such sets
provided you only utilize DBIx::Class::ResultSet CRUD methods: search, update, delete
For example, the following would not work (assuming "People" does not have a declared PK):
my $row = $schema->resultset('People')
->search({ last_name => 'Dantes' })
->next;
$row->update({ children => 2 }); # <-- exception thrown because $row isn't
# necessarily unique
So instead the following should be done:
$schema->resultset('People')
->search({ last_name => 'Dantes' })
->update({ children => 2 }); # <-- update's ALL Dantes to have children of 2
Problems on RHEL5/CentOS5
There used to be an issue with the system perl on Red Hat Enterprise Linux 5, some
versions of Fedora and derived systems. Further information on this can be found in
DBIx::Class::Manual::Troubleshooting
SEE ALSO
• DBIx::Class::Manual::Cookbook