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>.
107 See L<DBIx::Class::Relationship::Base> for a list of valid attributes.
113 =item Arguments: $accessor_name, $related_class, $foreign_key_column?, $attr?
117 # in a Book class (where Author has many Books)
118 My::DBIC::Schema::Book->belongs_to(author => 'My::DBIC::Schema::Author');
120 my $author_obj = $obj->author; # get author object
121 $obj->author($new_author_obj); # set author object
123 My::DBIC::Schema::Book->belongs_to(publisher =>
125 Creates a relationship where the calling class stores the foreign class's
126 primary key in one (or more) of its columns. If C<$cond> is a column name
127 instead of a join condition hash, it is used as the name of the foreign key
128 column in the calling class. If C<$cond> is not given, C<$accessor_name> is
129 used as the column name.
131 If the relationship is optional -- i.e. the column containing the foreign key
132 can be NULL -- then the belongs_to relationship does the right thing. Thus, in
133 the example above C<$obj-E<gt>author> would return C<undef>. However in this
134 case you would probably want to set the C<join_type> attribute so that a C<LEFT
135 JOIN> is done, which makes complex resultsets involving C<join> or C<prefetch>
136 operations work correctly. The modified declaration is shown below:
138 # in a Book class (where Author has_many Books)
139 __PACKAGE__->belongs_to(author => 'My::DBIC::Schema::Author',
140 'author', {join_type => 'left'});
143 Cascading deletes are off by default on a C<belongs_to>
144 relationship. To turn them on, pass C<< cascade_delete => 1 >>
145 in the $attr hashref.
147 NOTE: If you are used to L<Class::DBI> relationships, this is the equivalent
150 See L<DBIx::Class::Relationship::Base> for documentation on relationship methods.
156 =item Arguments: $accessor_name, $related_class, $foreign_key_column|$cond?, $attr?
160 # in an Author class (where Author has_many Books)
161 My::DBIC::Schema::Author->has_many(books => 'My::DBIC::Schema::Book', 'author');
163 my $booklist = $obj->books;
164 my $booklist = $obj->books({
165 name => { LIKE => '%macaroni%' },
166 { prefetch => [qw/book/],
168 my @book_objs = $obj->books;
169 my $books_rs = $obj->books;
170 ( $books_rs ) = $obj->books_rs;
172 $obj->add_to_books(\%col_data);
174 The above C<has_many> relationship could also have been specified with an
175 explicit join condition:
177 My::DBIC::Schema::Author->has_many( books => 'My::DBIC::Schema::Book', {
178 'foreign.author' => 'self.author',
181 Creates a one-to-many relationship, where the corresponding elements of the
182 foreign class store the calling class's primary key in one (or more) of its
183 columns. You should pass the name of the column in the foreign class as the
184 C<$cond> argument, or specify a complete join condition.
186 Three methods are created when you create a has_many relationship. The first
187 method is the expected accessor method, C<$accessor_name()>. The second is
188 almost exactly the same as the accessor method but "_rs" is added to the end of
189 the method name. This method works just like the normal accessor, except that
190 it returns a resultset no matter what, even in list context. The third method,
191 named C<< add_to_$relname >>, will also be added to your Row items; this
192 allows you to insert new related items, using the same mechanism as in
193 L<DBIx::Class::Relationship::Base/"create_related">.
195 If you delete an object in a class with a C<has_many> relationship, all
196 the related objects will be deleted as well. To turn this behaviour off,
197 pass C<< cascade_delete => 0 >> in the C<$attr> hashref. However, any
198 database-level cascade or restrict will take precedence over a
199 DBIx-Class-based cascading delete.
201 See L<DBIx::Class::Relationship::Base> for documentation on relationship methods.
207 =item Arguments: $accessor_name, $related_class, $join_condition?, $attr?
211 My::DBIC::Schema::Author->might_have(pseudonym =>
212 'My::DBIC::Schema::Pseudonym');
214 my $pname = $obj->pseudonym; # to get the Pseudonym object
216 Creates an optional one-to-one relationship with a class. This relationship
217 defaults to using C<$accessor_name> as the foreign key in C<$related_class>
218 to resolve the join, unless C<$join_condition> specifies a column in
219 C<$related_class> or a join condition hash reference.
221 If you update or delete an object in a class with a C<might_have>
222 relationship, the related object will be updated or deleted as well. To
223 turn off this behavior, add C<< cascade_delete => 0 >> to the C<$attr>
224 hashref. Any database-level update or delete constraints will override
227 See L<DBIx::Class::Relationship::Base> for more information.
233 =item Arguments: $accessor_name, $related_class_name, $join_condition?, $attr?
237 My::DBIC::Schema::Book->has_one(isbn => 'My::DBIC::Schema::ISBN');
239 my $isbn_obj = $obj->isbn; # to get the ISBN object
241 Creates a one-to-one relationship with another class. This is just like
242 C<might_have>, except the implication is that the other object is always
243 present. The only difference between C<has_one> and C<might_have> is that
244 C<has_one> uses an (ordinary) inner join, whereas C<might_have> uses a
247 The has_one relationship should be used when a row in the table has exactly one
248 related row in another table. If the related row might not exist in the foreign
249 table, use the L<DBIx::Class::Relationship/might_have> relationship.
251 In the above example, each Book in the database is associated with exactly one
254 See L<DBIx::Class::Relationship::Base> for documentation on relationship methods.
260 =item Arguments: $accessor_name, $link_rel_name, $foreign_rel_name, $attr?
264 To create a many_to_many relationship from Actor to Role:
266 My::DBIC::Schema::Actor->has_many( actor_roles =>
267 'My::DBIC::Schema::ActorRoles',
269 My::DBIC::Schema::ActorRoles->belongs_to( role =>
270 'My::DBIC::Schema::Role' );
271 My::DBIC::Schema::ActorRoles->belongs_to( actor =>
272 'My::DBIC::Schema::Actor' );
274 My::DBIC::Schema::Actor->many_to_many( roles => 'actor_roles',
277 And, for the reverse relationship, from Role to Actor:
279 My::DBIC::Schema::Role->has_many( actor_roles =>
280 'My::DBIC::Schema::ActorRoles',
283 My::DBIC::Schema::Role->many_to_many( actors => 'actor_roles', 'actor' );
285 Creates accessors bridging two relationships; not strictly a relationship in
286 its own right, although the accessor will return a resultset or collection of
287 objects just as a has_many would.
289 In the above example, ActorRoles is the link table class, and Role is the
290 foreign class. The C<$link_rel_name> parameter is the name of the accessor for
291 the has_many relationship from this table to the link table, and the
292 C<$foreign_rel_name> parameter is the accessor for the belongs_to relationship
293 from the link table to the foreign table.
295 To use many_to_many, existing relationships from the original table to the link
296 table, and from the link table to the end table must already exist, these
297 relation names are then used in the many_to_many call.
299 In the above example, the Actor class will have 3 many_to_many accessor methods
300 set: C<$roles>, C<$add_to_roles>, C<$set_roles>, and similarly named accessors
301 will be created for the Role class for the C<actors> many_to_many
304 See L<DBIx::Class::Relationship::Base> for documentation on relationship methods.
312 Matt S. Trout <mst@shadowcatsystems.co.uk>
316 You may distribute this code under the same terms as Perl itself.