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 and valid
108 relationship attributes.
114 =item Arguments: $accessor_name, $related_class, $foreign_key_column|$cond?, $attr?
118 # in a Book class (where Author has many Books)
119 My::DBIC::Schema::Book->belongs_to( author => 'My::DBIC::Schema::Author' );
121 my $author_obj = $obj->author; # get author object
122 $obj->author( $new_author_obj ); # set author object
124 The above belongs_to relationship could also have been specified as,
126 My::DBIC::Schema::Book->belongs_to( author,
127 'My::DBIC::Schema::Author',
128 { 'foreign.author' => 'self.author' } );
130 Creates a relationship where the calling class stores the foreign class's
131 primary key in one (or more) of its columns. This relationship defaults to
132 using C<$accessor_name> as the foreign key in C<$related_class> to resolve the
133 join, unless C<$foreign_key_column> specifies the foreign key column in
134 C<$related_class> or C<$cond> specifies a reference to a join condition hash.
136 If the relationship is optional -- i.e. the column containing the foreign key
137 can be NULL -- then the belongs_to relationship does the right thing. Thus, in
138 the example above C<$obj-E<gt>author> would return C<undef>. However in this
139 case you would probably want to set the C<join_type> attribute so that a C<LEFT
140 JOIN> is done, which makes complex resultsets involving C<join> or C<prefetch>
141 operations work correctly. The modified declaration is shown below:
143 # in a Book class (where Author has_many Books)
144 __PACKAGE__->belongs_to(author => 'My::DBIC::Schema::Author',
145 'author', {join_type => 'left'});
148 Cascading deletes are off by default on a C<belongs_to>
149 relationship. To turn them on, pass C<< cascade_delete => 1 >>
150 in the $attr hashref.
152 NOTE: If you are used to L<Class::DBI> relationships, this is the equivalent
155 See L<DBIx::Class::Relationship::Base> for documentation on relationship
156 methods and valid relationship attributes.
162 =item Arguments: $accessor_name, $related_class, $foreign_key_column|$cond?, $attr?
166 # in an Author class (where Author has_many Books)
167 My::DBIC::Schema::Author->has_many(books => 'My::DBIC::Schema::Book', 'author');
169 my $booklist = $obj->books;
170 my $booklist = $obj->books({
171 name => { LIKE => '%macaroni%' },
172 { prefetch => [qw/book/],
174 my @book_objs = $obj->books;
175 my $books_rs = $obj->books;
176 ( $books_rs ) = $obj->books_rs;
178 $obj->add_to_books(\%col_data);
180 The above C<has_many> relationship could also have been specified with an
181 explicit join condition:
183 My::DBIC::Schema::Author->has_many( books => 'My::DBIC::Schema::Book', {
184 'foreign.author' => 'self.author',
187 Creates a one-to-many relationship, where the corresponding elements of the
188 foreign class store the calling class's primary key in one (or more) of its
189 columns. This relationship defaults to using C<$accessor_name> as the foreign
190 key in C<$related_class> to resolve the join, unless C<$foreign_key_column>
191 specifies the foreign key column in C<$related_class> or C<$cond> specifies a
192 reference to a join condition hash.
194 Three methods are created when you create a has_many relationship. The first
195 method is the expected accessor method, C<$accessor_name()>. The second is
196 almost exactly the same as the accessor method but "_rs" is added to the end of
197 the method name. This method works just like the normal accessor, except that
198 it returns a resultset no matter what, even in list context. The third method,
199 named C<< add_to_$relname >>, will also be added to your Row items; this
200 allows you to insert new related items, using the same mechanism as in
201 L<DBIx::Class::Relationship::Base/"create_related">.
203 If you delete an object in a class with a C<has_many> relationship, all
204 the related objects will be deleted as well. To turn this behaviour off,
205 pass C<< cascade_delete => 0 >> in the C<$attr> hashref. However, any
206 database-level cascade or restrict will take precedence over a
207 DBIx-Class-based cascading delete.
209 See L<DBIx::Class::Relationship::Base> for documentation on relationship
210 methods and valid relationship attributes.
216 =item Arguments: $accessor_name, $related_class, $foreign_key_column|$cond?, $attr?
220 My::DBIC::Schema::Author->might_have( pseudonym =>
221 'My::DBIC::Schema::Pseudonym' );
223 my $pname = $obj->pseudonym; # to get the Pseudonym object
225 The above might_have relationship could have been specified as:
227 My::DBIC::Schema::Author->might_have( pseudonym =>
228 'My::DBIC::Schema::Pseudonym',
233 My::DBIC::Schema::Author->might_have( pseudonym =>
234 'My::DBIC::Schema::Pseudonym',
235 { 'foreign.author' => 'self.author' } );
237 Assuming the Pseudonym table has
239 Creates an optional one-to-one relationship with a class. This relationship
240 defaults to using C<$accessor_name> as the foreign key in C<$related_class> to
241 resolve the join, unless C<$foreign_key_column> specifies the foreign key
242 column in C<$related_class> or C<$cond> specifies a reference to a join
245 If you update or delete an object in a class with a C<might_have>
246 relationship, the related object will be updated or deleted as well. To
247 turn off this behavior, add C<< cascade_delete => 0 >> to the C<$attr>
248 hashref. Any database-level update or delete constraints will override
251 See L<DBIx::Class::Relationship::Base> for documentation on relationship
252 methods and valid relationship attributes.
258 =item Arguments: $accessor_name, $related_class_name, $join_condition?, $attr?
262 My::DBIC::Schema::Book->has_one(isbn => 'My::DBIC::Schema::ISBN');
264 my $isbn_obj = $obj->isbn; # to get the ISBN object
266 Creates a one-to-one relationship with another class. This is just like
267 C<might_have>, except the implication is that the other object is always
268 present. The only difference between C<has_one> and C<might_have> is that
269 C<has_one> uses an (ordinary) inner join, whereas C<might_have> uses a
272 The has_one relationship should be used when a row in the table has exactly one
273 related row in another table. If the related row might not exist in the foreign
274 table, use the L<DBIx::Class::Relationship/might_have> relationship.
276 In the above example, each Book in the database is associated with exactly one
279 See L<DBIx::Class::Relationship::Base> for documentation on relationship
280 methods and valid relationship attributes.
286 =item Arguments: $accessor_name, $link_rel_name, $foreign_rel_name, $attr?
290 To create a many_to_many relationship from Actor to Role:
292 My::DBIC::Schema::Actor->has_many( actor_roles =>
293 'My::DBIC::Schema::ActorRoles',
295 My::DBIC::Schema::ActorRoles->belongs_to( role =>
296 'My::DBIC::Schema::Role' );
297 My::DBIC::Schema::ActorRoles->belongs_to( actor =>
298 'My::DBIC::Schema::Actor' );
300 My::DBIC::Schema::Actor->many_to_many( roles => 'actor_roles',
303 And, for the reverse relationship, from Role to Actor:
305 My::DBIC::Schema::Role->has_many( actor_roles =>
306 'My::DBIC::Schema::ActorRoles',
309 My::DBIC::Schema::Role->many_to_many( actors => 'actor_roles', 'actor' );
311 To add a role for your actor, and fill in the year of the role in the
314 $actor->add_to_roles($role, { year => 1995 });
316 Many_to_many is not strictly a relationship in its own right. Instead, it is
317 a bridge between two resultsets which provide the same kind of convenience
318 accessors as true relationships provide. Although the accessor will return a
319 resultset or collection of objects just like has_many does, you cannot call
320 C<$related_resultset> and similar methods which operate on true relationships.
322 In the above example, ActorRoles is the link table class, and Role is the
323 foreign class. The C<$link_rel_name> parameter is the name of the accessor for
324 the has_many relationship from this table to the link table, and the
325 C<$foreign_rel_name> parameter is the accessor for the belongs_to relationship
326 from the link table to the foreign table.
328 To use many_to_many, existing relationships from the original table to the link
329 table, and from the link table to the end table must already exist, these
330 relation names are then used in the many_to_many call.
332 In the above example, the Actor class will have 3 many_to_many accessor methods
333 set: C<$roles>, C<$add_to_roles>, C<$set_roles>, and similarly named accessors
334 will be created for the Role class for the C<actors> many_to_many
337 See L<DBIx::Class::Relationship::Base> for documentation on relationship
338 methods and valid relationship attributes.
346 Matt S. Trout <mst@shadowcatsystems.co.uk>
350 You may distribute this code under the same terms as Perl itself.