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/ DBIx::Class::Manual::Intro

NAME

DBIx::Class::Manual::Intro - Introduction to DBIx::Class

INTRODUCTION

So, you are 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 ResultSources

DBIx::Class needs to know what your Table structure looks like. You do that by defining DBIx::Class::ResultSources. Each table get's a ResultSource, 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 ResultSource == 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 it's 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.

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_classes() method. You can specify which classes to load manually:

# load My::Schema::Album and My::Schema::Artist
__PACKAGE__->load_classes(qw/ Album Artist /);

Or load classes by namespace:

# load My::Schema::Album, My::Schema::Artist and My::OtherSchema::LinerNotes
__PACKAGE__->load_classes(
  {
    'My::Schema' => [qw/ Album Artist /],
    'My::OtherSchema' => [qw/ LinerNotes /]
  }
);

Or let your schema class load all classes in its namespace automatically:

 # load My::Schema::*
__PACKAGE__->load_classes();

Next, create each of the classes you want to load as specified above:

package My::Schema::Album;
use base qw/DBIx::Class/;

Load any components required by each class with the load_components() method. This should consist of "Core" plus any additional components you want to use. For example, if you want serial/auto-incrementing primary keys:

__PACKAGE__->load_components(qw/ PK::Auto Core /);

PK::Auto is supported for many databases; see DBIx::Class::Storage::DBI for more information.

Set the table for your class:

__PACKAGE__->table('album');

Add columns to your class:

__PACKAGE__->add_columns(qw/ albumid artist title /);

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 such as:

__PACKAGE__->add_columns(albumid =>
                          { accessor  => 'album',
                            data_type => 'integer',
                            size      => 16,
                            is_nullable => 0,
                            is_auto_increment => 1,
                            default_value => '',
                          },
                        artist =>
                          { data_type => 'integer',
                            size      => 16,
                            is_nullable => 0,
                            is_auto_increment => 0,
                            default_value => '',
                          },
                        title  => 
                          { data_type => 'varchar',
                            size      => 256,
                            is_nullable => 0,
                            is_auto_increment => 0,
                            default_value => '',
                          }
                       );

Most of this data isn't yet used directly by DBIx::Class, but various related modules such as DBIx::Class::WebForm make use of it. Also it allows you to create your database tables from your Schema, instead of the other way around. See SQL::Translator for details.

See DBIx::Class::ResultSource for more details of the possible column attributes.

Accessors are created for each column automatically, so My::Schema::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 relationships that the class has with any other classes by 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 tables foreign key in one of their columns:

__PACKAGE__->has_many('albums', 'My::Schema::Artist', 'album_id');

More information about the various types of relationships available, and how you can design your own, can be found in DBIx::Class::Relationship.

Using DBIx::Class::Schema::Loader

This is an external module, and not part of the DBIx::Class distribution. Like Class::DBI::Loader, it inspects your database, and automatically creates classes for all the tables in your database. Here's a simple setup:

package My::Schema;
use base qw/DBIx::Class::Schema::Loader/;

__PACKAGE__->load_from_connection(
  connect_info = [ 'dbi:SQLite:/home/me/myapp/my.db' ]
);

1;

This should be equivalent to the manual setup in the section above. DBIx::Class::Schema::Loader takes lots of other options. For more information, consult its documentation.

Connecting

DBIx::Class::Schema::Loader already contains the connection info for the database, so to get started all you need to do is create an instance of your class:

my $schema = My::Schema->new();

To connect to your manually created Schema, you also need to provide the connection details:

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 pass them to your schema after the connect:

$schema->storage->on_connect_do(\@on_connect_sql_statments);

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::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 commit your changes to the database:

$album->update;

If needed, you can throw away your local changes like this:

$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::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 like this:

$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 });

For more information on what you can do with a DBIx::Class::ResultSet, see "METHODS" in DBIx::Class::ResultSet.

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, like:

# 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 => [ 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 => 'year DESC' }
);

@albums then holds the two most recent Bob Marley albums.

For a complete overview of the available attributes, see "ATTRIBUTES" in DBIx::Class::ResultSet.

SEE ALSO