Added startup checks to warn loudly if we appear to be running on RedHat systems...

[dbsrgits/DBIx-Class.git] / lib / DBIx / Class / Manual / Intro.pod

=head1 NAME

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

=head1 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 L<Class::DBI>, and think there's a
better way?  You've come to the right place.

=head1 THE DBIx::Class WAY

Here are a few simple tips that will help you get your bearings with
DBIx::Class.  

=head2 Tables become ResultSources

DBIx::Class needs to know what your Table structure looks like.  You do that by
defining L<DBIx::Class::ResultSource>s.  Each table gets 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)

=head2 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 L<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.

=head2 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.

=head1 SETTING UP DBIx::Class

Let's look at how you can set and use your first native L<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
L<DBIx::Class::Schema::Loader>.

=head2 Setting it up manually

First, you should create your base schema class, which inherits from
L<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 /);

C<PK::Auto> is supported for many databases; see L<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 C<add_columns> a hash:

  __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 => '',
                            }
                         );

DBIx::Class doesn't directly use most of this data yet, but various related
modules such as L<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 L<SQL::Translator> for details.

See L<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 this class' relationships with other classes using either C<belongs_to>
to describe a column which contains an ID of another Table, or C<has_many> to
make a predefined accessor for fetching objects that contain this Table's
foreign key:

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

See L<DBIx::Class::Relationship> for more information about the various types of
available relationships and how you can design your own.

=head2 Using L<DBIx::Class::Schema::Loader>

This is an external module, and not part of the L<DBIx::Class> distribution.
Like L<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__->loader_options( relationships => 1 );

  1;

The actual autoloading process will occur when you create a connected instance
of your schema below.

See the L<DBIx::Class::Schema::Loader> documentation for more information on its
many options.

=head2 Connecting

To connect to your Schema, you need to provide the connection details.  The
arguments are the same as for L<DBI/connect>:

  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 L<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 L<DBIx::Class::Schema::Storage::DBI/connect_info> for more information about
this and other special C<connect>-time options.

=head2 Basic usage

Once you've defined the basic classes, either manually or using
L<DBIx::Class::Schema::Loader>, you can start interacting with your database.

To access your database using your $schema object, you can fetch a
L<DBIx::Class::Manual::Glossary/"ResultSet"> representing each of your tables by
calling the C<resultset> method.

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

  my $album = $schema->resultset('Album')->find(14);

This will run a C<SELECT> with C<albumid = 14> in the C<WHERE> clause, and
return an instance of C<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 C<set_column> and C<get_column> accessors
instead:

  $album->set_column('title', 'Presence');
  $title = $album->get_column('title');

Just like with L<Class::DBI>, you call C<update> to commit your changes to the
database:

  $album->update;

If needed, you can throw away your local changes:

  $album->discard_changes if $album->is_changed;

As you can see, C<is_changed> allows you to check if there are local changes to
your object.

=head2 Adding and removing rows

To create a new record in the database, you can use the C<create> method.  It
returns an instance of C<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:

  $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;

=head2 Finding your objects

L<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, C<search> returns a L<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 C<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 C<LIKE> search:

  # Find albums whose artist starts with 'Jimi'
  my $rs = $schema->resultset('Album')->search_like({ artist => 'Jimi%' });

Or you can provide your own C<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 L<SQL::Abstract>
construct to C<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 C<WHERE> clause:

  WHERE artist != 'Janis Joplin'
    AND year < 1980
    AND albumid IN (1, 14, 15, 65, 43)

For more examples of complex queries, see L<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' }
  );

C<@albums> then holds the two most recent Bob Marley albums.

For more information on what you can do with a L<DBIx::Class::ResultSet>, see
L<DBIx::Class::ResultSet/METHODS>.

For a complete overview of the available attributes, see
L<DBIx::Class::ResultSet/ATTRIBUTES>.

=head1 NOTES

=head2 Problems on RHEL5/CentOS5

There is a problem with slow performance of certain DBIx::Class operations in
perl-5.8.8-10 and later on RedHat and related systems, due to a bad backport of
a "use overload" related bug.  The problem is in the Perl binary itself, not in
DBIx::Class.  If your system has this problem, you will see a warning on
startup, with some options as to what to do about it.

=head1 SEE ALSO

=over 4

=item * L<DBIx::Class::Manual::Cookbook>

=back

=cut