Base
/);
-=head1 NAME
+=head1 NAME
DBIx::Class::Relationship - Inter-table relationships
=head1 SYNOPSIS
+ MyDB::Schema::Actor->has_many('actorroles' => 'MyDB::Schema::ActorRole',
+ 'actor');
+ MyDB::Schema::Role->has_many('actorroles' => 'MyDB::Schema::ActorRole',
+ 'role');
+ MyDB::Schema::ActorRole->belongs_to('role' => 'MyDB::Schema::Role');
+ MyDB::Schema::ActorRole->belongs_to('actor' => 'MyDB::Schema::Actor');
+
+ MyDB::Schema::Role->many_to_many('actors' => 'actorroles', 'actor');
+ MyDB::Schema::Actor->many_to_many('roles' => 'actorroles', 'role');
+
+ $schema->resultset('Actor')->roles();
+ $schema->resultset('Role')->search_related('actors', { Name => 'Fred' });
+ $schema->resultset('ActorRole')->add_to_roles({ Name => 'Sherlock Holmes'});
+
+See L<DBIx::Class::Manual::Cookbook> for more.
+
=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
+are documented here. For the basic, lower-level methods, and a description
+of all the useful *_related methods that you get for free, see
L<DBIx::Class::Relationship::Base>.
=head1 METHODS
=head2 belongs_to
- # in a Bar class (where Foo has many Bars)
- __PACKAGE__->belongs_to(foo => Foo);
- my $f_obj = $obj->foo;
- $obj->foo($new_f_obj);
+ # in a Book class (where Author has many Books)
+ My::DBIC::Schema::Book->belongs_to(author => 'My::DBIC::Schema::Author');
+ my $author_obj = $obj->author;
+ $obj->author($new_author_obj);
-Creates a relationship where the calling class stores the foreign class's
+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.
+Cascading deletes are off per default on a C<belongs_to> relationship, to turn
+them on, pass C<< cascade_delete => 1 >> in the $attr hashref.
+
NOTE: If you are used to L<Class::DBI> relationships, this is the equivalent
of C<has_a>.
=head2 has_many
- # in a Foo class (where Foo has many Bars)
- __PACKAGE__->has_many(bar => Bar, 'foo');
- my $f_resultset = $obj->foo;
- my $f_resultset = $obj->foo({ name => { LIKE => '%macaroni%' }, { prefetch => [qw/bar/] });
- my @f_obj = $obj->foo;
+ # in an Author class (where Author has many Books)
+ My::DBIC::Schema::Author->has_many(books => 'My::DBIC::Schema::Book', 'author');
+ my $booklist = $obj->books;
+ my $booklist = $obj->books({
+ name => { LIKE => '%macaroni%' },
+ { prefetch => [qw/book/],
+ });
+ my @book_objs = $obj->books;
+ my $books_rs = $obj->books;
+ ( $books_rs ) = $obj->books_rs;
- $obj->add_to_foo(\%col_data);
+ $obj->add_to_books(\%col_data);
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.
+Three methods are created when you create a has_many relationship. The first
+method is the expected accessor method. The second is almost exactly the same
+as the accessor method but "_rs" is added to the end of the method name. This
+method works just like the normal accessor, except that it returns a resultset
+no matter what, even in list context. The third method, named
+C<< add_to_<relname> >>, will also be added to your Row items, this allows
+you to insert new related items, using the same mechanism as in
+L<DBIx::Class::Relationship::Base/"create_related">.
+
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.
+the related objects will be deleted as well. However, any database-level
+cascade or restrict will take precedence. To turn this behavior off, pass
+C<< cascade_delete => 0 >> in the $attr hashref.
=head2 might_have
- __PACKAGE__->might_have(baz => Baz);
- my $f_obj = $obj->baz; # to get the baz object
+ My::DBIC::Schema::Author->might_have(pseudonym =>
+ 'My::DBIC::Schema::Pseudonyms');
+ my $pname = $obj->pseudonym; # to get the Pseudonym object
-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.
+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.
-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 behavior.
+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.
+To turn off this behavior, add C<< cascade_delete => 0 >> to the $attr hashref.
=head2 has_one
- __PACKAGE__->has_one(gorch => Gorch);
- my $f_obj = $obj->gorch;
+ My::DBIC::Schema::Book->has_one(isbn => 'My::DBIC::Schema::ISBN');
+ my $isbn_obj = $obj->isbn;
+
+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.
+
+
+=head2 many_to_many
+
+=over 4
+
+=item Arguments: $accessor_name, $link_rel_name, $foreign_rel_name
+
+=back
+
+ My::DBIC::Schema::Actor->has_many( actor_roles =>
+ 'My::DBIC::Schema::ActorRoles',
+ 'actor' );
+ My::DBIC::Schema::ActorRoles->belongs_to( role =>
+ 'My::DBIC::Schema::Role' );
+ My::DBIC::Schema::ActorRoles->belongs_to( actor =>
+ 'My::DBIC::Schema::Actor' );
+
+ My::DBIC::Schema::Actor->many_to_many( roles => 'actor_roles',
+ 'role' );
+
+Creates a accessors 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.
+
+To use many_to_many, existing relationships from the original table to the link
+table, and from the link table to the end table must already exist, these
+relation names are then used in the many_to_many call.
+
+=head3 Created accessors
+
+=head4 $rel
+
+=over 4
+
+=item Arguments: $vals?, $attrs
+
+=back
+
+ my $role_rs = $actor->roles;
+
+ my $role1 = $actor->roles({ name => 'role1' })->first;
+
+Returns a resultset for the foreign table on the right side of the
+many-to-many relationship. (e.g., in the above example, a CD's
+producers). Takes the same arguments as L<DBIx::Class::ResultSet/"search">.
+
+=head4 add_to_$rel
+
+=over 4
+
+=item Arguments: ($foreign_vals | $obj), $link_vals?
+
+=back
+
+ my $role = $schema->resultset('Role')->find(1);
+ $actor->add_to_roles($role);
+ # creates a My::DBIC::Schema::ActorRoles linking table row object
+
+ $actor->add_to_roles({ name => 'lead' }, { salary => 15_000_000 });
+ # creates a new My::DBIC::Schema::Role row object and the linking table
+ # object with an extra column in the link
+
+Adds a linking table object for C<$obj> or C<$foreign_vals>. If the first
+argument is a hash reference, the related object is created first with the
+column values in the hash. If an object reference is given, just the linking
+table object is created. In either case, any additional column values for the
+linking table object can be specified in C<$link_vals>.
+
+=head4 remove_from_$rel
+
+=over 4
+
+=item Arguments: $obj
-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 different
-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.
+=back
+ my $role = $schema->resultset('Role')->find(1);
+ $actor->remove_from_roles($role);
+ # removes $role's My::DBIC::Schema::ActorRoles linking table row object
-=head2 many_to_many
-
- __PACKAGE__->many_to_many( 'accessorname' => 'a_to_b', 'table_b' );
- my @f_objs = $obj_a->accessorname;
+Removes the link between the current object and the related object. Note that
+the related object itself won't be deleted unless you call ->delete() on
+it. This method just removes the link between the two objects.
=cut
projects / dbsrgits/DBIx-Class.git / blobdiff