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')->find({ id => 1})->roles();
35 $schema->resultset('Role')->find({ id => 1 })->actorroles->search_related('actor', { Name => 'Fred' });
36 $schema->resultset('Actor')->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, $foreign_key_column|\%cond|\@cond?, \%attr?
225 Creates a one-to-many relationship, where the corresponding elements
226 of the foreign class store the calling class's primary key in one (or
227 more) of its columns. This relationship defaults to using the end of
228 this classes namespace as the foreign key in C<$related_class> to
229 resolve the join, unless C<$foreign_key_column> specifies the foreign
230 key column in C<$related_class> or C<cond> specifies a reference to a
237 This argument is the name of the method you can call on a
238 L<DBIx::Class::Row> object to retrieve a resultset of the related
239 class restricted to the ones related to the row object. In list
240 context it returns the row objects. This is often called the
241 C<relation(ship) name>.
243 Use this accessor_name in L<DBIx::Class::ResultSet/join>
244 or L<DBIx::Class::ResultSet/prefetch> to join to the foreign table
245 indicated by this relationship.
249 This is the class name of the table which contains a foreign key
250 column containing PK values of this class.
252 =item foreign_key_column
254 The column name on the related class that contains the foreign key.
260 A hashref where the keys are C<foreign.$foreign_key_column> and
261 the values are C<self.$matching_column>. This is useful for
262 relations that are across multiple columns.
266 An arrayref containing an SQL::Abstract-like condition. For example a
267 link table where two columns link back to the same table. This is an
270 My::Schema::Item->has_many('rels', 'My::Schema::Relationships',
271 [ { 'foreign.LItemID' => 'self.ID' },
272 { 'foreign.RItemID' => 'self.ID'} ]);
276 # in an Author class (where Author has_many Books)
277 # assuming related class is storing our PK in "author_id"
278 My::DBIC::Schema::Author->has_many(
280 'My::DBIC::Schema::Book',
285 My::DBIC::Schema::Author->has_many(
287 'My::DBIC::Schema::Book',
288 { 'foreign.author_id' => 'self.id' },
291 # OR (similar result, assuming related_class is storing our PK, in "author")
292 # (the "author" is guessed at from "Author" in the class namespace)
293 My::DBIC::Schema::Author->has_many(
295 'My::DBIC::Schema::Book',
300 # resultset of Books belonging to author
301 my $booklist = $author->books;
303 # resultset of Books belonging to author, restricted by author name
304 my $booklist = $author->books({
305 name => { LIKE => '%macaroni%' },
306 { prefetch => [qw/book/],
309 # array of Book objects belonging to author
310 my @book_objs = $author->books;
312 # force resultset even in list context
313 my $books_rs = $author->books;
314 ( $books_rs ) = $obj->books_rs;
316 # create a new book for this author, the relation fields are auto-filled
317 $author->create_related('books', \%col_data);
318 # alternative method for the above
319 $author->add_to_books(\%col_data);
322 Three methods are created when you create a has_many relationship. The first
323 method is the expected accessor method, C<$accessor_name()>. The second is
324 almost exactly the same as the accessor method but "_rs" is added to the end of
325 the method name. This method works just like the normal accessor, except that
326 it always returns a resultset, even in list context. The third method,
327 named C<< add_to_$relname >>, will also be added to your Row items; this
328 allows you to insert new related items, using the same mechanism as in
329 L<DBIx::Class::Relationship::Base/"create_related">.
331 If you delete an object in a class with a C<has_many> relationship, all
332 the related objects will be deleted as well. To turn this behaviour off,
333 pass C<< cascade_delete => 0 >> in the C<$attr> hashref.
335 The cascaded operations are performed after the requested delete or
336 update, so if your database has a constraint on the relationship, it
337 will have deleted/updated the related records or raised an exception
338 before DBIx::Class gets to perform the cascaded operation.
340 If you copy an object in a class with a C<has_many> relationship, all
341 the related objects will be copied as well. To turn this behaviour off,
342 pass C<< cascade_copy => 0 >> in the C<$attr> hashref. The behaviour
343 defaults to C<< cascade_copy => 1 >>.
345 See L<DBIx::Class::Relationship::Base> for documentation on relationship
346 methods and valid relationship attributes.
352 =item Arguments: $accessor_name, $related_class, $foreign_key_column|\%cond|\@cond?, \%attr?
356 Creates an optional one-to-one relationship with a class. This relationship
357 defaults to using C<$accessor_name> as the foreign key in C<$related_class> to
358 resolve the join, unless C<$foreign_key_column> specifies the foreign key
359 column in C<$related_class> or C<cond> specifies a reference to a join
366 This argument is the name of the method you can call on a
367 L<DBIx::Class::Row> object to retrieve the instance of the foreign
368 class matching this relationship. This is often called the
369 C<relation(ship) name>.
371 Use this accessor_name in L<DBIx::Class::ResultSet/join>
372 or L<DBIx::Class::ResultSet/prefetch> to join to the foreign table
373 indicated by this relationship.
377 This is the class name of the table which contains a foreign key
378 column containing PK values of this class.
380 =item foreign_key_column
382 The column name on the related class that contains the foreign key.
388 A hashref where the keys are C<foreign.$column_on_related_table> and
389 the values are C<self.$matching_column>. This is useful for
390 relations that are across multiple columns.
394 # Author may have an entry in the pseudonym table
395 My::DBIC::Schema::Author->might_have(
397 'My::DBIC::Schema::Pseudonym',
401 # OR (same result, assuming the related_class stores our PK)
402 My::DBIC::Schema::Author->might_have(
404 'My::DBIC::Schema::Pseudonym',
408 My::DBIC::Schema::Author->might_have(
410 'My::DBIC::Schema::Pseudonym',
411 { 'foreign.author_id' => 'self.id' },
415 my $pname = $author->pseudonym; # to get the Pseudonym object
417 If you update or delete an object in a class with a C<might_have>
418 relationship, the related object will be updated or deleted as well. To
419 turn off this behavior, add C<< cascade_delete => 0 >> to the C<$attr>
422 The cascaded operations are performed after the requested delete or
423 update, so if your database has a constraint on the relationship, it
424 will have deleted/updated the related records or raised an exception
425 before DBIx::Class gets to perform the cascaded operation.
427 See L<DBIx::Class::Relationship::Base> for documentation on relationship
428 methods and valid relationship attributes.
434 =item Arguments: $accessor_name, $related_class, $foreign_key_column|\%cond|\@cond?, \%attr?
438 Creates a one-to-one relationship with a class. This relationship
439 defaults to using C<$accessor_name> as the foreign key in C<$related_class> to
440 resolve the join, unless C<$foreign_key_column> specifies the foreign key
441 column in C<$related_class> or C<cond> specifies a reference to a join
448 This argument is the name of the method you can call on a
449 L<DBIx::Class::Row> object to retrieve the instance of the foreign
450 class matching this relationship. This is often called the
451 C<relation(ship) name>.
453 Use this accessor_name in L<DBIx::Class::ResultSet/join>
454 or L<DBIx::Class::ResultSet/prefetch> to join to the foreign table
455 indicated by this relationship.
459 This is the class name of the table which contains a foreign key
460 column containing PK values of this class.
462 =item foreign_key_column
464 The column name on the related class that contains the foreign key.
470 A hashref where the keys are C<foreign.$column_on_related_table> and
471 the values are C<self.$matching_column>. This is useful for
472 relations that are across multiple columns.
476 # Every book has exactly one ISBN
477 My::DBIC::Schema::Book->has_one(
479 'My::DBIC::Schema::ISBN',
483 # OR (same result, assuming related_class stores our PK)
484 My::DBIC::Schema::Book->has_one(
486 'My::DBIC::Schema::ISBN',
490 My::DBIC::Schema::Book->has_one(
492 'My::DBIC::Schema::ISBN',
493 { 'foreign.book_id' => 'self.id' },
497 my $isbn_obj = $book->isbn; # to get the ISBN object
499 Creates a one-to-one relationship with another class. This is just
500 like C<might_have>, except the implication is that the other object is
501 always present. The only difference between C<has_one> and
502 C<might_have> is that C<has_one> uses an (ordinary) inner join,
503 whereas C<might_have> defaults to a left join.
505 The has_one relationship should be used when a row in the table has exactly one
506 related row in another table. If the related row might not exist in the foreign
507 table, use the L<DBIx::Class::Relationship/might_have> relationship.
509 In the above example, each Book in the database is associated with exactly one
512 See L<DBIx::Class::Relationship::Base> for documentation on relationship
513 methods and valid relationship attributes.
519 =item Arguments: $accessor_name, $link_rel_name, $foreign_rel_name, \%attr?
523 C<many_to_many> is not strictly a relationship in its own right. Instead, it is
524 a bridge between two resultsets which provide the same kind of convenience
525 accessors as true relationships provide. Although the accessor will return a
526 resultset or collection of objects just like has_many does, you cannot call
527 C<related_resultset> and similar methods which operate on true relationships.
533 This argument is the name of the method you can call on a
534 L<DBIx::Class::Row> object to retrieve the rows matching this
537 On a many_to_many, unlike other relationships, this cannot be used in
538 L<DBIx::Class::ResultSet/search> to join tables. Use the relations
539 bridged across instead.
543 This is the accessor_name from the has_many relationship we are
546 =item foreign_rel_name
548 This is the accessor_name of the belongs_to relationship in the link
549 table that we are bridging across (which gives us the table we are
554 To create a many_to_many relationship from Actor to Role:
556 My::DBIC::Schema::Actor->has_many( actor_roles =>
557 'My::DBIC::Schema::ActorRoles',
559 My::DBIC::Schema::ActorRoles->belongs_to( role =>
560 'My::DBIC::Schema::Role' );
561 My::DBIC::Schema::ActorRoles->belongs_to( actor =>
562 'My::DBIC::Schema::Actor' );
564 My::DBIC::Schema::Actor->many_to_many( roles => 'actor_roles',
567 And, for the reverse relationship, from Role to Actor:
569 My::DBIC::Schema::Role->has_many( actor_roles =>
570 'My::DBIC::Schema::ActorRoles',
573 My::DBIC::Schema::Role->many_to_many( actors => 'actor_roles', 'actor' );
575 To add a role for your actor, and fill in the year of the role in the
578 $actor->add_to_roles($role, { year => 1995 });
580 In the above example, ActorRoles is the link table class, and Role is the
581 foreign class. The C<$link_rel_name> parameter is the name of the accessor for
582 the has_many relationship from this table to the link table, and the
583 C<$foreign_rel_name> parameter is the accessor for the belongs_to relationship
584 from the link table to the foreign table.
586 To use many_to_many, existing relationships from the original table to the link
587 table, and from the link table to the end table must already exist, these
588 relation names are then used in the many_to_many call.
590 In the above example, the Actor class will have 3 many_to_many accessor methods
591 set: C<roles>, C<add_to_roles>, C<set_roles>, and similarly named accessors
592 will be created for the Role class for the C<actors> many_to_many
595 See L<DBIx::Class::Relationship::Base> for documentation on relationship
596 methods and valid relationship attributes.
608 You may distribute this code under the same terms as Perl itself.