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 Cascading deletes are off per default on a C<belongs_to> relationship, to turn
122 them on, pass C<< cascade_delete => 1 >> in the $attr hashref.
124 NOTE: If you are used to L<Class::DBI> relationships, this is the equivalent
129 # in an Author class (where Author has many Books)
130 My::DBIC::Schema::Author->has_many(books => 'My::DBIC::Schema::Book', 'author');
131 my $booklist = $obj->books;
132 my $booklist = $obj->books({
133 name => { LIKE => '%macaroni%' },
134 { prefetch => [qw/book/],
136 my @book_objs = $obj->books;
138 $obj->add_to_books(\%col_data);
140 Creates a one-to-many relationship, where the corresponding elements of the
141 foreign class store the calling class's primary key in one (or more) of its
142 columns. You should pass the name of the column in the foreign class as the
143 $cond argument, or specify a complete join condition.
145 As well as the accessor method, a method named C<< add_to_<relname> >>
146 will also be added to your Row items, this allows you to insert new
147 related items, using the same mechanism as in L<DBIx::Class::Relationship::Base/"create_related">.
149 If you delete an object in a class with a C<has_many> relationship, all
150 the related objects will be deleted as well. However, any database-level
151 cascade or restrict will take precedence. To turn this behavior off, pass
152 C<< cascade_delete => 0 >> in the $attr hashref.
156 My::DBIC::Schema::Author->might_have(pseudonym =>
157 'My::DBIC::Schema::Pseudonyms');
158 my $pname = $obj->pseudonym; # to get the Pseudonym object
160 Creates an optional one-to-one relationship with a class, where the foreign
161 class stores our primary key in one of its columns. Defaults to the primary
162 key of the foreign class unless $cond specifies a column or join condition.
164 If you update or delete an object in a class with a C<might_have>
165 relationship, the related object will be updated or deleted as well.
166 Any database-level update or delete constraints will override this behaviour.
167 To turn off this behavior, add C<< cascade_delete => 0 >> to the $attr hashref.
171 My::DBIC::Schema::Book->has_one(isbn => 'My::DBIC::Schema::ISBN');
172 my $isbn_obj = $obj->isbn;
174 Creates a one-to-one relationship with another class. This is just like
175 C<might_have>, except the implication is that the other object is always
176 present. The only difference between C<has_one> and C<might_have> is that
177 C<has_one> uses an (ordinary) inner join, whereas C<might_have> uses a
183 My::DBIC::Schema::Actor->has_many( actor_roles =>
184 'My::DBIC::Schema::ActorRoles',
186 My::DBIC::Schema::ActorRoles->belongs_to( role =>
187 'My::DBIC::Schema::Role' );
188 My::DBIC::Schema::ActorRoles->belongs_to( actor =>
189 'My::DBIC::Schema::Actor' );
191 My::DBIC::Schema::Actor->many_to_many( roles => 'actor_roles',
196 my @role_objs = $actor->roles;
198 Creates an accessor bridging two relationships; not strictly a relationship
199 in its own right, although the accessor will return a resultset or collection
200 of objects just as a has_many would.
201 To use many_to_many, existing relationships from the original table to the link
202 table, and from the link table to the end table must already exist, these
203 relation names are then used in the many_to_many call.
211 Matt S. Trout <mst@shadowcatsystems.co.uk>
215 You may distribute this code under the same terms as Perl itself.