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 ## Creating relationships
23 MyDB::Schema::Actor->has_many('actorroles' => 'MyDB::Schema::ActorRole',
25 MyDB::Schema::Role->has_many('actorroles' => 'MyDB::Schema::ActorRole',
27 MyDB::Schema::ActorRole->belongs_to('role' => 'MyDB::Schema::Role');
28 MyDB::Schema::ActorRole->belongs_to('actor' => 'MyDB::Schema::Actor');
30 MyDB::Schema::Role->many_to_many('actors' => 'actorroles', 'actor');
31 MyDB::Schema::Actor->many_to_many('roles' => 'actorroles', 'role');
33 ## Using relationships
34 $schema->resultset('Actor')->roles();
35 $schema->resultset('Role')->search_related('actors', { Name => 'Fred' });
36 $schema->resultset('ActorRole')->add_to_roles({ Name => 'Sherlock Holmes'});
38 See L<DBIx::Class::Manual::Cookbook> for more.
42 This class provides methods to set up relationships between the tables
43 in your database model. Relationships are the most useful and powerful
44 technique that L<DBIx::Class> provides. To create efficient database queries,
45 create relationships between any and all tables that have something in
46 common, for example if you have a table Authors:
57 1 | 1 | Rulers of the universe
58 2 | 1 | Rulers of the galaxy
60 Then without relationships, the method of getting all books by Fred goes like
63 my $fred = $schema->resultset('Author')->find({ Name => 'Fred' });
64 my $fredsbooks = $schema->resultset('Book')->search({ Author => $fred->ID });
66 With a has_many relationship called "books" on Author (see below for details),
67 we can do this instead:
69 my $fredsbooks = $schema->resultset('Author')->find({ Name => 'Fred' })->books;
71 Each relationship sets up an accessor method on the
72 L<DBIx::Class::Manual::Glossary/"Row"> objects that represent the items
73 of your table. From L<DBIx::Class::Manual::Glossary/"ResultSet"> objects,
74 the relationships can be searched using the "search_related" method.
75 In list context, each returns a list of Row objects for the related class,
76 in scalar context, a new ResultSet representing the joined tables is
77 returned. Thus, the calls can be chained to produce complex queries.
78 Since the database is not actually queried until you attempt to retrieve
79 the data for an actual item, no time is wasted producing them.
81 my $cheapfredbooks = $schema->resultset('Author')->find({
83 })->books->search_related('prices', {
84 Price => { '<=' => '5.00' },
87 will produce a query something like:
89 SELECT * FROM Author me
90 LEFT JOIN Books books ON books.author = me.id
91 LEFT JOIN Prices prices ON prices.book = books.id
92 WHERE prices.Price <= 5.00
94 all without needing multiple fetches.
96 Only the helper methods for setting up standard relationship types
97 are documented here. For the basic, lower-level methods, and a description
98 of all the useful *_related methods that you get for free, see
99 L<DBIx::Class::Relationship::Base>.
103 All helper methods are called similar to the following template:
105 __PACKAGE__->$method_name('relname', 'Foreign::Class', $cond, $attrs);
107 Both C<$cond> and C<$attrs> are optional. Pass C<undef> for C<$cond> if
108 you want to use the default value for it, but still want to set C<$attrs>.
110 See L<DBIx::Class::Relationship::Base> for documentation on the
111 attrubutes that are allowed in the C<$attrs> argument.
118 =item Arguments: $accessor_name, $related_class, $fk_column|\%cond|\@cond?, \%attr?
122 Creates a relationship where the calling class stores the foreign
123 class's primary key in one (or more) of its columns. This relationship
124 defaults to using C<$accessor_name> as the column in this class
125 to resolve the join against the primary key from C<$related_class>,
126 unless C<$fk_column> specifies the foreign key column in this class or
127 C<cond> specifies a reference to a join condition hash.
133 This argument is the name of the method you can call on a
134 L<DBIx::Class::Row> object to retrieve the instance of the foreign
135 class matching this relationship. This is often called the
136 C<relation(ship) name>.
138 Use this accessor_name in L<DBIx::Class::ResultSet/join>
139 or L<DBIx::Class::ResultSet/prefetch> to join to the foreign table
140 indicated by this relationship.
144 This is the class name of the table referenced by the foreign key in
149 The column name on this class that contains the foreign key.
155 A hashref where the keys are C<foreign.$column_on_related_table> and
156 the values are C<self.$foreign_key_column>. This is useful for
157 relations that are across multiple columns.
162 # in a Book class (where Author has many Books)
163 My::DBIC::Schema::Book->belongs_to(
165 'My::DBIC::Schema::Author',
170 My::DBIC::Schema::Book->belongs_to(
172 'My::DBIC::Schema::Author',
173 { 'foreign.author_id' => 'self.author_id' }
176 # OR (similar result but uglier accessor name)
177 My::DBIC::Schema::Book->belongs_to(
179 'My::DBIC::Schema::Author'
183 my $author_obj = $book->author; # get author object
184 $book->author( $new_author_obj ); # set author object
185 $book->author_id(); # get the plain id
187 # To retrieve the plain id if you used the ugly version:
188 $book->get_column('author_id');
191 If the relationship is optional -- i.e. the column containing the foreign key
192 can be NULL -- then the belongs_to relationship does the right thing. Thus, in
193 the example above C<$obj-E<gt>author> would return C<undef>. However in this
194 case you would probably want to set the C<join_type> attribute so that a C<LEFT
195 JOIN> is done, which makes complex resultsets involving C<join> or C<prefetch>
196 operations work correctly. The modified declaration is shown below:
198 # in a Book class (where Author has_many Books)
199 __PACKAGE__->belongs_to(
201 'My::DBIC::Schema::Author',
203 { join_type => 'left' }
207 Cascading deletes are off by default on a C<belongs_to>
208 relationship. To turn them on, pass C<< cascade_delete => 1 >>
209 in the $attr hashref.
211 NOTE: If you are used to L<Class::DBI> relationships, this is the equivalent
214 See L<DBIx::Class::Relationship::Base> for documentation on relationship
215 methods and valid relationship attributes.
221 =item Arguments: $accessor_name, $related_class, $foreign_key_column|\%cond|\@cond?, \%attr?
225 Creates a one-to-many relationship, where the corresponding elements of the
226 foreign class store the calling class's primary key in one (or more) of its
227 columns. This relationship defaults to using C<$accessor_name> as the foreign
228 key in C<$related_class> to resolve the join, unless C<$foreign_key_column>
229 specifies the foreign key column in C<$related_class> or C<cond> specifies a
230 reference to a join condition hash.
236 This argument is the name of the method you can call on a
237 L<DBIx::Class::Row> object to retrieve a resultset of the related
238 class restricted to the ones related to the row object. In list
239 context it returns the row objects. This is often called the
240 C<relation(ship) name>.
242 Use this accessor_name in L<DBIx::Class::ResultSet/join>
243 or L<DBIx::Class::ResultSet/prefetch> to join to the foreign table
244 indicated by this relationship.
248 This is the class name of the table which contains a foreign key
249 column containing PK values of this class.
251 =item foreign_key_column
253 The column name on the related class that contains the foreign key.
259 A hashref where the keys are C<foreign.$foreign_key_column> and
260 the values are C<self.$matching_column>. This is useful for
261 relations that are across multiple columns.
265 An arrayref containing an SQL::Abstract-like condition. For example a
266 link table where two columns link back to the same table. This is an
269 My::Schema::Item->has_many('rels', 'My::Schema::Relationships',
270 [ { 'foreign.LItemID' => 'self.ID' },
271 { 'foreign.RItemID' => 'self.ID'} ]);
274 # in an Author class (where Author has_many Books)
275 My::DBIC::Schema::Author->has_many(
277 'My::DBIC::Schema::Book',
281 # OR (same result, assuming related_class is storing our PK)
282 My::DBIC::Schema::Author->has_many(
284 'My::DBIC::Schema::Book',
288 My::DBIC::Schema::Author->has_many(
290 'My::DBIC::Schema::Book',
291 { 'foreign.author_id' => 'self.id' },
296 # resultset of Books belonging to author
297 my $booklist = $author->books;
299 # resultset of Books belonging to author, restricted by author name
300 my $booklist = $author->books({
301 name => { LIKE => '%macaroni%' },
302 { prefetch => [qw/book/],
305 # array of Book objects belonging to author
306 my @book_objs = $author->books;
308 # force resultset even in list context
309 my $books_rs = $author->books;
310 ( $books_rs ) = $obj->books_rs;
312 # create a new book for this author, the relation fields are auto-filled
313 $author->create_related('books', \%col_data);
314 # alternative method for the above
315 $author->add_to_books(\%col_data);
318 Three methods are created when you create a has_many relationship. The first
319 method is the expected accessor method, C<$accessor_name()>. The second is
320 almost exactly the same as the accessor method but "_rs" is added to the end of
321 the method name. This method works just like the normal accessor, except that
322 it always returns a resultset, even in list context. The third method,
323 named C<< add_to_$relname >>, will also be added to your Row items; this
324 allows you to insert new related items, using the same mechanism as in
325 L<DBIx::Class::Relationship::Base/"create_related">.
327 If you delete an object in a class with a C<has_many> relationship, all
328 the related objects will be deleted as well. To turn this behaviour off,
329 pass C<< cascade_delete => 0 >> in the C<attr> hashref. However, any
330 database-level cascade or restrict will take precedence over a
331 DBIx-Class-based cascading delete.
333 If you copy an object in a class with a C<has_many> relationship, all
334 the related objects will be copied as well. To turn this behaviour off,
335 pass C<< cascade_copy => 0 >> in the C<$attr> hashref. The behaviour
336 defaults to C<< cascade_copy => 1 >>.
338 See L<DBIx::Class::Relationship::Base> for documentation on relationship
339 methods and valid relationship attributes.
345 =item Arguments: $accessor_name, $related_class, $foreign_key_column|\%cond|\@cond?, \%attr?
349 Creates an optional one-to-one relationship with a class. This relationship
350 defaults to using C<$accessor_name> as the foreign key in C<$related_class> to
351 resolve the join, unless C<$foreign_key_column> specifies the foreign key
352 column in C<$related_class> or C<cond> specifies a reference to a join
359 This argument is the name of the method you can call on a
360 L<DBIx::Class::Row> object to retrieve the instance of the foreign
361 class matching this relationship. This is often called the
362 C<relation(ship) name>.
364 Use this accessor_name in L<DBIx::Class::ResultSet/join>
365 or L<DBIx::Class::ResultSet/prefetch> to join to the foreign table
366 indicated by this relationship.
370 This is the class name of the table which contains a foreign key
371 column containing PK values of this class.
373 =item foreign_key_column
375 The column name on the related class that contains the foreign key.
381 A hashref where the keys are C<foreign.$column_on_related_table> and
382 the values are C<self.$foreign_key_column>. This is useful for
383 relations that are across multiple columns.
387 # Author may have an entry in the pseudonym table
388 My::DBIC::Schema::Author->might_have(
390 'My::DBIC::Schema::Pseudonym',
394 # OR (same result, assuming the related_class stores our PK)
395 My::DBIC::Schema::Author->might_have(
397 'My::DBIC::Schema::Pseudonym',
401 My::DBIC::Schema::Author->might_have(
403 'My::DBIC::Schema::Pseudonym',
404 { 'foreign.author_id' => 'self.id' },
408 my $pname = $author->pseudonym; # to get the Pseudonym object
410 If you update or delete an object in a class with a C<might_have>
411 relationship, the related object will be updated or deleted as well. To
412 turn off this behavior, add C<< cascade_delete => 0 >> to the C<$attr>
413 hashref. Any database-level update or delete constraints will override
416 See L<DBIx::Class::Relationship::Base> for documentation on relationship
417 methods and valid relationship attributes.
423 =item Arguments: $accessor_name, $related_class, $foreign_key_column|\%cond|\@cond?, \%attr?
427 Creates a one-to-one relationship with a class. This relationship
428 defaults to using C<$accessor_name> as the foreign key in C<$related_class> to
429 resolve the join, unless C<$foreign_key_column> specifies the foreign key
430 column in C<$related_class> or C<cond> specifies a reference to a join
437 This argument is the name of the method you can call on a
438 L<DBIx::Class::Row> object to retrieve the instance of the foreign
439 class matching this relationship. This is often called the
440 C<relation(ship) name>.
442 Use this accessor_name in L<DBIx::Class::ResultSet/join>
443 or L<DBIx::Class::ResultSet/prefetch> to join to the foreign table
444 indicated by this relationship.
448 This is the class name of the table which contains a foreign key
449 column containing PK values of this class.
451 =item foreign_key_column
453 The column name on the related class that contains the foreign key.
459 A hashref where the keys are C<foreign.$column_on_related_table> and
460 the values are C<self.$foreign_key_column>. This is useful for
461 relations that are across multiple columns.
465 # Every book has exactly one ISBN
466 My::DBIC::Schema::Book->has_one(
468 'My::DBIC::Schema::ISBN',
472 # OR (same result, assuming related_class stores our PK)
473 My::DBIC::Schema::Book->has_one(
475 'My::DBIC::Schema::ISBN',
479 My::DBIC::Schema::Book->has_one(
481 'My::DBIC::Schema::ISBN',
482 { 'foreign.book_id' => 'self.id' },
486 my $isbn_obj = $book->isbn; # to get the ISBN object
488 Creates a one-to-one relationship with another class. This is just
489 like C<might_have>, except the implication is that the other object is
490 always present. The only difference between C<has_one> and
491 C<might_have> is that C<has_one> uses an (ordinary) inner join,
492 whereas C<might_have> defaults to a left join.
494 The has_one relationship should be used when a row in the table has exactly one
495 related row in another table. If the related row might not exist in the foreign
496 table, use the L<DBIx::Class::Relationship/might_have> relationship.
498 In the above example, each Book in the database is associated with exactly one
501 See L<DBIx::Class::Relationship::Base> for documentation on relationship
502 methods and valid relationship attributes.
508 =item Arguments: $accessor_name, $link_rel_name, $foreign_rel_name, \%attr?
512 C<many_to_many> is not strictly a relationship in its own right. Instead, it is
513 a bridge between two resultsets which provide the same kind of convenience
514 accessors as true relationships provide. Although the accessor will return a
515 resultset or collection of objects just like has_many does, you cannot call
516 C<related_resultset> and similar methods which operate on true relationships.
522 This argument is the name of the method you can call on a
523 L<DBIx::Class::Row> object to retrieve the rows matching this
526 On a many_to_many, unlike other relationships, this cannot be used in
527 L<DBIx::Class::ResultSet/search> to join tables. Use the relations
528 bridged across instead.
532 This is the accessor_name from the has_many relationship we are
535 =item foreign_rel_name
537 This is the accessor_name of the belongs_to relationship in the link
538 table that we are bridging across (which gives us the table we are
543 To create a many_to_many relationship from Actor to Role:
545 My::DBIC::Schema::Actor->has_many( actor_roles =>
546 'My::DBIC::Schema::ActorRoles',
548 My::DBIC::Schema::ActorRoles->belongs_to( role =>
549 'My::DBIC::Schema::Role' );
550 My::DBIC::Schema::ActorRoles->belongs_to( actor =>
551 'My::DBIC::Schema::Actor' );
553 My::DBIC::Schema::Actor->many_to_many( roles => 'actor_roles',
556 And, for the reverse relationship, from Role to Actor:
558 My::DBIC::Schema::Role->has_many( actor_roles =>
559 'My::DBIC::Schema::ActorRoles',
562 My::DBIC::Schema::Role->many_to_many( actors => 'actor_roles', 'actor' );
564 To add a role for your actor, and fill in the year of the role in the
567 $actor->add_to_roles($role, { year => 1995 });
569 In the above example, ActorRoles is the link table class, and Role is the
570 foreign class. The C<$link_rel_name> parameter is the name of the accessor for
571 the has_many relationship from this table to the link table, and the
572 C<$foreign_rel_name> parameter is the accessor for the belongs_to relationship
573 from the link table to the foreign table.
575 To use many_to_many, existing relationships from the original table to the link
576 table, and from the link table to the end table must already exist, these
577 relation names are then used in the many_to_many call.
579 In the above example, the Actor class will have 3 many_to_many accessor methods
580 set: C<roles>, C<add_to_roles>, C<set_roles>, and similarly named accessors
581 will be created for the Role class for the C<actors> many_to_many
584 See L<DBIx::Class::Relationship::Base> for documentation on relationship
585 methods and valid relationship attributes.
597 You may distribute this code under the same terms as Perl itself.