use base qw/DBIx::Class/;
__PACKAGE__->load_own_components(qw/
- HasMany
- HasOne
- BelongsTo
+ Helpers
Accessor
CascadeActions
ProxyMethods
Base
/);
-__PACKAGE__->mk_classdata('_relationships', { } );
-
-=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
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 => 'My::DBIC::Schema::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
+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.
-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:
+NOTE: If you are used to L<Class::DBI> relationships, this is the equivalent
+of C<has_a>.
+
+=head2 has_many
+
+ # 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;
+
+ $obj->add_to_books(\%col_data);
+
+Creates a one-to-many relationship, where the corresponding elements of the
+foreign class store the calling class's primary key in one (or more) of its
+columns. You should pass the name of the column in the foreign class as the
+$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
+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
+
+ 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.
+
+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
+
+ 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.
- my $obj = Foo->find(1);
- $obj->margle(10); # set margle; Bar object is created if it doesn't exist
+
+=head2 many_to_many
+
+=over 4
+
+=item Arguments: $accessor_name, $link_rel_name, $foreign_rel_name
=back
-=head2 belongs_to
+ 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 $f_obj = $obj->relname;
+ My::DBIC::Schema::Actor->many_to_many( roles => 'actor_roles',
+ 'role' );
- $obj->relname($new_f_obj);
+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.
-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.
+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.
-=head2 has_many
+=head3 Created accessors
- my @f_obj = $obj->relname($cond?, $attrs?);
- my $f_result_set = $obj->relname($cond?, $attrs?);
+=head4 $rel
- $obj->add_to_relname(\%col_data);
+ my $role_rs = $actor->roles;
-Creates a one-many relationship with another class;
+ my $role1 = $actor->roles({ name => 'role1' })->first;
-=head2 might_have
+Returns a resultset for the table on the far-right side of the many-to-many
+relationship. (e.g., in the above example, a CD's producers).
- my $f_obj = $obj->relname;
+=head4 add_to_$rel
-Creates an optional one-one relationship with another class; defaults to PK-PK
-for the join condition unless a condition is specified.
+ my $role = $schema->resultset('Role')->find(1);
+ $actor->add_to_roles($role);
+ # creates a My::DBIC::Schema::ActorRoles linking table row object
-=head2 has_one
+ $actor->add_to_roles({ name => 'role1' });
+ # creates a new My::DBIC::Schema::Role row object, as well as the
+ # linking table object
+
+Adds a linking table object for the specified object, or if a hash is given
+instead the related object is created before the linking table object is
+created.
+
+=head4 remove_from_$rel
- my $f_obj = $obj->relname;
+ my $role = $schema->resultset('Role')->find(1);
+ $actor->remove_from_roles($role);
+ # removes $role's My::DBIC::Schema::ActorRoles linking table row object
-Creates a one-one relationship with another class; defaults to PK-PK for
-the join condition unless a condition is specified.
+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