1 package DBIx::Class::Relationship;
6 use base qw/DBIx::Class/;
8 __PACKAGE__->load_own_components(qw/
18 DBIx::Class::Relationship - Inter-table relationships
22 MyDB::Schema::Actor->has_many('actorroles' => 'MyDB::Schema::ActorRole',
24 MyDB::Schema::Role->has_many('actorroles' => 'MyDB::Schema::ActorRole',
26 MyDB::Schema::ActorRole->belongs_to('role' => 'MyDB::Schema::Role');
27 MyDB::Schema::ActorRole->belongs_to('actor' => 'MyDB::Schema::Actor');
29 MyDB::Schema::Role->many_to_many('actors' => 'actorroles', 'actor');
30 MyDB::Schema::Actor->many_to_many('roles' => 'actorroles', 'role');
32 $schema->resultset('Actor')->roles();
33 $schema->resultset('Role')->search_related('actors', { Name => 'Fred' });
34 $schema->resultset('ActorRole')->add_to_roles({ Name => 'Sherlock Holmes'});
36 See L<DBIx::Class::Manual::Cookbook> for more.
40 This class provides methods to set up relationships between the tables
41 in your database model. Relationships are the most useful and powerful
42 technique that L<DBIx::Class> provides. To create efficient database queries,
43 create relationships between any and all tables that have something in
44 common, for example if you have a table Authors:
55 1 | 1 | Rulers of the universe
56 2 | 1 | Rulers of the galaxy
58 Then without relationships, the method of getting all books by Fred goes like
61 my $fred = $schema->resultset('Author')->find({ Name => 'Fred' });
62 my $fredsbooks = $schema->resultset('Book')->search({ Author => $fred->ID });
63 With a has_many relationship called "books" on Author (see below for details),
64 we can do this instead:
66 my $fredsbooks = $schema->resultset('Author')->find({ Name => 'Fred' })->books;
68 Each relationship sets up an accessor method on the
69 L<DBIx::Class::Manual::Glossary/"Row"> objects that represent the items
70 of your table. From L<DBIx::Class::Manual::Glossary/"ResultSet"> objects,
71 the relationships can be searched using the "search_related" method.
72 In list context, each returns a list of Row objects for the related class,
73 in scalar context, a new ResultSet representing the joined tables is
74 returned. Thus, the calls can be chained to produce complex queries.
75 Since the database is not actually queried until you attempt to retrieve
76 the data for an actual item, no time is wasted producing them.
78 my $cheapfredbooks = $schema->resultset('Author')->find({
80 })->books->search_related('prices', {
81 Price => { '<=' => '5.00' },
84 will produce a query something like:
86 SELECT * FROM Author me
87 LEFT JOIN Books books ON books.author = me.id
88 LEFT JOIN Prices prices ON prices.book = books.id
89 WHERE prices.Price <= 5.00
91 all without needing multiple fetches.
93 Only the helper methods for setting up standard relationship types
94 are documented here. For the basic, lower-level methods, and a description
95 of all the useful *_related methods that you get for free, see
96 L<DBIx::Class::Relationship::Base>.
100 All helper methods take the following arguments:
102 __PACKAGE__>$method_name('relname', 'Foreign::Class', $cond, $attrs);
104 Both C<$cond> and C<$attrs> are optional. Pass C<undef> for C<$cond> if
105 you want to use the default value for it, but still want to set C<$attrs>.
106 See L<DBIx::Class::Relationship::Base> for a list of valid attributes.
110 # in a Book class (where Author has many Books)
111 My::DBIC::Schema::Book->belongs_to(author => 'My::DBIC::Schema::Author');
112 my $author_obj = $obj->author;
113 $obj->author($new_author_obj);
115 Creates a relationship where the calling class stores the foreign class's
116 primary key in one (or more) of its columns. If $cond is a column name
117 instead of a join condition hash, that is used as the name of the column
118 holding the foreign key. If $cond is not given, the relname is used as
121 NOTE: If you are used to L<Class::DBI> relationships, this is the equivalent
126 # in an Author class (where Author has many Books)
127 My::DBIC::Schema::Author->has_many(books => 'My::DBIC::Schema::Book', 'author');
128 my $booklist = $obj->books;
129 my $booklist = $obj->books({
130 name => { LIKE => '%macaroni%' },
131 { prefetch => [qw/book/],
133 my @book_objs = $obj->books;
134 my $books_rs = $obj->books;
135 ( $books_rs ) = $obj->books_rs;
137 $obj->add_to_books(\%col_data);
139 Creates a one-to-many relationship, where the corresponding elements of the
140 foreign class store the calling class's primary key in one (or more) of its
141 columns. You should pass the name of the column in the foreign class as the
142 $cond argument, or specify a complete join condition.
144 Three methods are created when you create a has_many relationship. The first
145 method is the expected accessor method. The second is almost exactly the same
146 as the accessor method but "_rs" is added to the end of the method name. This
147 method works just like the normal accessor, except that it returns a resultset
148 no matter what, even in list context. The third method, named
149 C<< add_to_<relname> >>, will also be added to your Row items, this allows
150 you to insert new related items, using the same mechanism as in
151 L<DBIx::Class::Relationship::Base/"create_related">.
153 If you delete an object in a class with a C<has_many> relationship, all
154 related objects will be deleted as well. However, any database-level
155 cascade or restrict will take precedence.
159 My::DBIC::Schema::Author->might_have(pseudonym =>
160 'My::DBIC::Schema::Pseudonyms');
161 my $pname = $obj->pseudonym; # to get the Pseudonym object
163 Creates an optional one-to-one relationship with a class, where the foreign
164 class stores our primary key in one of its columns. Defaults to the primary
165 key of the foreign class unless $cond specifies a column or join condition.
167 If you update or delete an object in a class with a C<might_have>
168 relationship, the related object will be updated or deleted as well.
169 Any database-level update or delete constraints will override this behaviour.
173 My::DBIC::Schema::Book->has_one(isbn => 'My::DBIC::Schema::ISBN');
174 my $isbn_obj = $obj->isbn;
176 Creates a one-to-one relationship with another class. This is just like
177 C<might_have>, except the implication is that the other object is always
178 present. The only difference between C<has_one> and C<might_have> is that
179 C<has_one> uses an (ordinary) inner join, whereas C<might_have> uses a
185 My::DBIC::Schema::Actor->has_many( actor_roles =>
186 'My::DBIC::Schema::ActorRoles',
188 My::DBIC::Schema::ActorRoles->belongs_to( role =>
189 'My::DBIC::Schema::Role' );
190 My::DBIC::Schema::ActorRoles->belongs_to( actor =>
191 'My::DBIC::Schema::Actor' );
193 My::DBIC::Schema::Actor->many_to_many( roles => 'actor_roles',
198 my @role_objs = $actor->roles;
200 Creates an accessor bridging two relationships; not strictly a relationship
201 in its own right, although the accessor will return a resultset or collection
202 of objects just as a has_many would.
203 To use many_to_many, existing relationships from the original table to the link
204 table, and from the link table to the end table must already exist, these
205 relation names are then used in the many_to_many call.
213 Matt S. Trout <mst@shadowcatsystems.co.uk>
217 You may distribute this code under the same terms as Perl itself.