use base qw/DBIx::Class/;
__PACKAGE__->load_own_components(qw/
- HasMany
- HasOne
- BelongsTo
+ Helpers
Accessor
CascadeActions
ProxyMethods
Base
/);
-__PACKAGE__->mk_classdata('_relationships', { } );
-
=head1 NAME
DBIx::Class::Relationship - Inter-table relationships
=head1 DESCRIPTION
-This class handles relationships between the tables in your database
-model. It allows you to set up relationships and perform joins on them.
+This class provides methods to set up relationships between the tables
+in your database model. Relationships are the most useful and powerful
+technique that L<DBIx::Class> provides. To create efficient database queries,
+create relationships between any and all tables that have something in
+common, for example if you have a table Authors:
+
+ ID | Name | Age
+ ------------------
+ 1 | Fred | 30
+ 2 | Joe | 32
+
+and a table Books:
+
+ ID | Author | Name
+ --------------------
+ 1 | 1 | Rulers of the universe
+ 2 | 1 | Rulers of the galaxy
+
+Then without relationships, the method of getting all books by Fred goes like
+this:
+
+ my $fred = $schema->resultset('Author')->find({ Name => 'Fred' });
+ my $fredsbooks = $schema->resultset('Book')->search({ Author => $fred->ID });
+With a has_many relationship called "books" on Author (see below for details),
+we can do this instead:
+
+ my $fredsbooks = $schema->resultset('Author')->find({ Name => 'Fred' })->books;
+
+Each relationship sets up an accessor method on the
+L<DBIx::Class::Manual::Glossary/"Row"> objects that represent the items
+of your table. From L<DBIx::Class::Manual::Glossary/"ResultSet"> objects,
+the relationships can be searched using the "search_related" method.
+In list context, each returns a list of Row objects for the related class,
+in scalar context, a new ResultSet representing the joined tables is
+returned. Thus, the calls can be chained to produce complex queries.
+Since the database is not actually queried until you attempt to retrieve
+the data for an actual item, no time is wasted producing them.
+
+ my $cheapfredbooks = $schema->resultset('Author')->find({
+ Name => 'Fred',
+ })->books->search_related('prices', {
+ Price => { '<=' => '5.00' },
+ });
+
+will produce a query something like:
+
+ SELECT * FROM Author me
+ LEFT JOIN Books books ON books.author = me.id
+ LEFT JOIN Prices prices ON prices.book = books.id
+ WHERE prices.Price <= 5.00
+
+all without needing multiple fetches.
Only the helper methods for setting up standard relationship types
are documented here. For the basic, lower-level methods, see
All helper methods take the following arguments:
- __PACKAGE__>method_name('relname', 'Foreign::Class', $cond, $attrs);
+ __PACKAGE__>$method_name('relname', 'Foreign::Class', $cond, $attrs);
Both C<$cond> and C<$attrs> are optional. Pass C<undef> for C<$cond> if
you want to use the default value for it, but still want to set C<$attrs>.
-The following attributes are recognize:
+See L<DBIx::Class::Relationship::Base> for a list of valid attributes.
-=over 4
+=head2 belongs_to
-=item join_type
+ # in a Book class (where Author has many Books)
+ My::DBIC::Schema::Book->belongs_to(author => 'Author');
+ my $author_obj = $obj->author;
+ $obj->author($new_author_obj);
-Explicitly specifies the type of join to use in the relationship. Any SQL
-join type is valid, e.g. C<LEFT> or C<RIGHT>. It will be placed in the SQL
-command immediately before C<JOIN>.
+Creates a relationship where the calling class stores the foreign class's
+primary key in one (or more) of its columns. If $cond is a column name
+instead of a join condition hash, that is used as the name of the column
+holding the foreign key. If $cond is not given, the relname is used as
+the column name.
-=item proxy
+NOTE: If you are used to L<Class::DBI> relationships, this is the equivalent
+of C<has_a>.
-An arrayref containing a list of accessors in the foreign class to proxy in
-the main class. If, for example, you do the following:
-
- __PACKAGE__->might_have(bar => 'Bar', undef, { proxy => qw[/ margle /] });
-
-Then, assuming Bar has an accessor named margle, you can do:
+=head2 has_many
- my $obj = Foo->find(1);
- $obj->margle(10); # set margle; Bar object is created if it doesn't exist
+ # in an Author class (where Author has many Books)
+ My::DBIC::Schema::Author->has_many(books => 'Book', 'author');
+ my $booklist = $obj->books;
+ my $booklist = $obj->books({
+ name => { LIKE => '%macaroni%' },
+ { prefetch => [qw/book/],
+ });
+ my @book_objs = $obj->books;
-=back
+ $obj->add_to_books(\%col_data);
-=head2 belongs_to
+Creates a one-to-many relationship, where the corresponding elements of the
+foreign class store the calling class's primary key in one (or more) of its
+columns. You should pass the name of the column in the foreign class as the
+$cond argument, or specify a complete join condition.
- my $f_obj = $obj->relname;
+If you delete an object in a class with a C<has_many> relationship, all
+related objects will be deleted as well. However, any database-level
+cascade or restrict will take precedence.
- $obj->relname($new_f_obj);
+=head2 might_have
-Creates a relationship where we store the foreign class' PK; if $join is a
-column name instead of a condition that is assumed to be the FK, if not
-has_many assumes the FK is the relname is that is a column on the current
-class.
+ My::DBIC::Schema::Author->might_have(psuedonym => 'Psuedonyms');
+ my $pname = $obj->psuedonym; # to get the Psuedonym object
-=head2 has_many
+Creates an optional one-to-one relationship with a class, where the foreign
+class stores our primary key in one of its columns. Defaults to the primary
+key of the foreign class unless $cond specifies a column or join condition.
- my @f_obj = $obj->relname($cond?, $attrs?);
- my $f_result_set = $obj->relname($cond?, $attrs?);
+If you update or delete an object in a class with a C<might_have>
+relationship, the related object will be updated or deleted as well.
+Any database-level update or delete constraints will override this behaviour.
- $obj->add_to_relname(\%col_data);
+=head2 has_one
-Creates a one-many relationship with another class;
+ My::DBIC::Schema::Book->has_one(isbn => ISBN);
+ my $isbn_obj = $obj->isbn;
-=head2 might_have
+Creates a one-to-one relationship with another class. This is just like
+C<might_have>, except the implication is that the other object is always
+present. The only difference between C<has_one> and C<might_have> is that
+C<has_one> uses an (ordinary) inner join, whereas C<might_have> uses a
+left join.
- my $f_obj = $obj->relname;
-Creates an optional one-one relationship with another class; defaults to PK-PK
-for the join condition unless a condition is specified.
+=head2 many_to_many
-=head2 has_one
+ My::DBIC::Schema::Actor->many_to_many( roles => 'actor_roles', 'Roles' );
+
+ ...
- my $f_obj = $obj->relname;
+ my @role_objs = $actor->roles;
-Creates a one-one relationship with another class; defaults to PK-PK for
-the join condition unless a condition is specified.
+Creates an accessor bridging two relationships; not strictly a relationship
+in its own right, although the accessor will return a resultset or collection
+of objects just as a has_many would.
=cut
projects / dbsrgits/DBIx-Class.git / blobdiff