David Kamholz > DBIx-Class-0.05006 > DBIx::Class::Manual::SchemaIntro

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NAME ^

DBIx::Class::Manual::SchemaIntro - Introduction to DBIx::Class::Schema

INTRODUCTION ^

This document describes how to set up DBIx::Class using the recommended schema-based approach.

Setup

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 use SQLite and want serial/auto-incrementing primary keys:

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

PK::Auto classes exist for many databases; see DBIx::Class::PK::Auto for more information.

Set the table for your class:

  __PACKAGE__->table('album');

Add columns to your class:

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

Accessors are created for each column automatically, so My::Schema::Album will have albumid(), 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 / );

You can define relationships for any of your classes. DBIx::Class will automatically fill in the correct namespace, so if you want to say "a My::Schema::Album object belongs to a My::Schema::Artist object" you do not need to include the namespace when declaring the relationship:

  __PACKAGE__->belongs_to('artist' => 'Artist');

That's all you need in terms of setup.

Usage

In your application code, you should first create a connected schema object:

  my $schema = My::Schema->connect( $dsn, $user, $password, $attrs );

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 connnections 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);

The simplest way to get a record is by primary key:

  my $schema = My::Schema->connect( ... );
  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; # 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');

You use 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 or retrieving first. This operation takes the same kind of arguments as a search.

  # Delete all of Falco's albums
  $schema->resultset('Album')->delete({ artist => 'Falco' });

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;

Or, 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;
  }

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 handmade 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 = $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 ^

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