Base
/);
+1;
+
+__END__
+
=head1 NAME
DBIx::Class::Relationship - Inter-table relationships
=head1 SYNOPSIS
## Creating relationships
- MyDB::Schema::Actor->has_many('actorroles' => 'MyDB::Schema::ActorRole',
+ MyApp::Schema::Actor->has_many('actorroles' => 'MyApp::Schema::ActorRole',
'actor');
- MyDB::Schema::Role->has_many('actorroles' => 'MyDB::Schema::ActorRole',
+ MyApp::Schema::Role->has_many('actorroles' => 'MyApp::Schema::ActorRole',
'role');
- MyDB::Schema::ActorRole->belongs_to('role' => 'MyDB::Schema::Role');
- MyDB::Schema::ActorRole->belongs_to('actor' => 'MyDB::Schema::Actor');
+ MyApp::Schema::ActorRole->belongs_to('role' => 'MyApp::Schema::Role');
+ MyApp::Schema::ActorRole->belongs_to('actor' => 'MyApp::Schema::Actor');
- MyDB::Schema::Role->many_to_many('actors' => 'actorroles', 'actor');
- MyDB::Schema::Actor->many_to_many('roles' => 'actorroles', 'role');
+ MyApp::Schema::Role->many_to_many('actors' => 'actorroles', 'actor');
+ MyApp::Schema::Actor->many_to_many('roles' => 'actorroles', 'role');
## Using relationships
$schema->resultset('Actor')->find({ id => 1})->roles();
=head1 DESCRIPTION
+The word I<Relationship> has a specific meaning in DBIx::Class, see
+the definition in the L<Glossary|DBIx::Class::Manual::Glossary/Relationship>.
+
This class provides methods to set up relationships between the tables
in your database model. Relationships are the most useful and powerful
technique that L<DBIx::Class> provides. To create efficient database queries,
my $fredsbooks = $schema->resultset('Author')->find({ Name => 'Fred' })->books;
Each relationship sets up an accessor method on the
-L<DBIx::Class::Manual::Glossary/"Row"> objects that represent the items
-of your table. From L<DBIx::Class::Manual::Glossary/"ResultSet"> objects,
+L<Result|DBIx::Class::Manual::Glossary/"Result"> objects that represent the items
+of your table. From L<ResultSet|DBIx::Class::Manual::Glossary/"ResultSet"> objects,
the relationships can be searched using the "search_related" method.
-In list context, each returns a list of Row objects for the related class,
+In list context, each returns a list of Result objects for the related class,
in scalar context, a new ResultSet representing the joined tables is
returned. Thus, the calls can be chained to produce complex queries.
Since the database is not actually queried until you attempt to retrieve
All helper methods are called similar to the following template:
- __PACKAGE__->$method_name('relname', 'Foreign::Class', $cond, $attrs);
-
-Both C<$cond> and C<$attrs> are optional. Pass C<undef> for C<$cond> if
-you want to use the default value for it, but still want to set C<$attrs>.
+ __PACKAGE__->$method_name('rel_name', 'Foreign::Class', \%cond|\@cond|\&cond?, \%attrs?);
+
+Both C<cond> and C<attrs> are optional. Pass C<undef> for C<cond> if
+you want to use the default value for it, but still want to set C<attrs>.
+
+See L<DBIx::Class::Relationship::Base/condition> for full documentation on
+definition of the C<cond> argument.
-See L<DBIx::Class::Relationship::Base> for documentation on the
-attrubutes that are allowed in the C<$attrs> argument.
+See L<DBIx::Class::Relationship::Base/attributes> for documentation on the
+attributes that are allowed in the C<attrs> argument.
=head2 belongs_to
=over 4
-=item Arguments: $accessor_name, $related_class, $our_fk_column|\%cond|\@cond?, \%attr?
+=item Arguments: $accessor_name, $related_class, $our_fk_column|\%cond|\@cond|\$cond?, \%attrs?
=back
This relationship defaults to using C<$accessor_name> as the column
name in this class to resolve the join against the primary key from
C<$related_class>, unless C<$our_fk_column> specifies the foreign key column
-in this class or C<cond> specifies a reference to a join condition hash.
+in this class or C<cond> specifies a reference to a join condition.
=over
=item accessor_name
This argument is the name of the method you can call on a
-L<DBIx::Class::Row> object to retrieve the instance of the foreign
+L<Result|DBIx::Class::Manual::ResultClass> object to retrieve the instance of the foreign
class matching this relationship. This is often called the
C<relation(ship) name>.
=item cond
-A hashref where the keys are C<foreign.$column_on_related_table> and
-the values are C<self.$our_fk_column>. This is useful for
-relations that are across multiple columns.
+A hashref, arrayref or coderef specifying a custom join expression. For
+more info see L<DBIx::Class::Relationship::Base/condition>.
=back
-
# in a Book class (where Author has many Books)
- My::DBIC::Schema::Book->belongs_to(
- author =>
- 'My::DBIC::Schema::Author',
+ My::DBIC::Schema::Book->belongs_to(
+ author =>
+ 'My::DBIC::Schema::Author',
'author_id'
);
My::DBIC::Schema::Book->belongs_to(
author =>
'My::DBIC::Schema::Author',
- { 'foreign.author_id' => 'self.author_id' }
+ { 'foreign.author_id' => 'self.author_id' }
);
# OR (similar result but uglier accessor name)
- My::DBIC::Schema::Book->belongs_to(
+ My::DBIC::Schema::Book->belongs_to(
author_id =>
'My::DBIC::Schema::Author'
);
# To retrieve the plain id if you used the ugly version:
$book->get_column('author_id');
-
-If the relationship is optional -- i.e. the column containing the foreign key
-can be NULL -- then the belongs_to relationship does the right thing. Thus, in
-the example above C<$obj-E<gt>author> would return C<undef>. However in this
-case you would probably want to set the C<join_type> attribute so that a C<LEFT
-JOIN> is done, which makes complex resultsets involving C<join> or C<prefetch>
-operations work correctly. The modified declaration is shown below:
+If some of the foreign key columns are
+L<nullable|DBIx::Class::ResultSource/is_nullable> you probably want to set
+the L<join_type|DBIx::Class::Relationship::Base/join_type> attribute to
+C<left> explicitly so that SQL expressing this relation is composed with
+a C<LEFT JOIN> (as opposed to C<INNER JOIN> which is default for
+L</belongs_to> relationships). This ensures that relationship traversal
+works consistently in all situations. (i.e. resultsets involving
+L<join|DBIx::Class::ResultSet/join> or
+L<prefetch|DBIx::Class::ResultSet/prefetch>).
+The modified declaration is shown below:
# in a Book class (where Author has_many Books)
__PACKAGE__->belongs_to(
- author =>
+ author =>
'My::DBIC::Schema::Author',
- 'author',
+ 'author',
{ join_type => 'left' }
);
-
Cascading deletes are off by default on a C<belongs_to>
relationship. To turn them on, pass C<< cascade_delete => 1 >>
in the $attr hashref.
+By default, DBIC will return undef and avoid querying the database if a
+C<belongs_to> accessor is called when any part of the foreign key IS NULL. To
+disable this behavior, pass C<< undef_on_null_fk => 0 >> in the C<\%attrs>
+hashref.
+
NOTE: If you are used to L<Class::DBI> relationships, this is the equivalent
of C<has_a>.
-See L<DBIx::Class::Relationship::Base> for documentation on relationship
+See L<DBIx::Class::Relationship::Base/attributes> for documentation on relationship
methods and valid relationship attributes. Also see L<DBIx::Class::ResultSet>
for a L<list of standard resultset attributes|DBIx::Class::ResultSet/ATTRIBUTES>
which can be assigned to relationships as well.
=over 4
-=item Arguments: $accessor_name, $related_class, $their_fk_column|\%cond|\@cond?, \%attr?
+=item Arguments: $accessor_name, $related_class, $their_fk_column|\%cond|\@cond|\&cond?, L<\%attrs?|DBIx::Class::ResultSet/ATTRIBUTES>
=back
-Creates a one-to-many relationship, where the corresponding elements
-of the foreign class store the calling class's primary key in one (or
-more) of the foreign class columns. This relationship defaults to using
-the end of this classes namespace as the foreign key in C<$related_class>
-to resolve the join, unless C<$their_fk_column> specifies the foreign
-key column in C<$related_class> or C<cond> specifies a reference to a
-join condition hash.
+Creates a one-to-many relationship where the foreign class refers to
+this class's primary key. This relationship refers to zero or more
+records in the foreign table (e.g. a C<LEFT JOIN>). This relationship
+defaults to using the end of this classes namespace as the foreign key
+in C<$related_class> to resolve the join, unless C<$their_fk_column>
+specifies the foreign key column in C<$related_class> or C<cond>
+specifies a reference to a join condition.
=over
=item accessor_name
This argument is the name of the method you can call on a
-L<DBIx::Class::Row> object to retrieve a resultset of the related
-class restricted to the ones related to the row object. In list
-context it returns the row objects. This is often called the
+L<Result|DBIx::Class::Manual::ResultClass> object to retrieve a resultset of the related
+class restricted to the ones related to the result object. In list
+context it returns the result objects. This is often called the
C<relation(ship) name>.
Use this accessor_name in L<DBIx::Class::ResultSet/join>
=item cond
-A hashref where the keys are C<foreign.$their_fk_column> and
-the values are C<self.$matching_column>. This is useful for
-relations that are across multiple columns.
-
-OR
-
-An arrayref containing an SQL::Abstract-like condition. For example a
-link table where two columns link back to the same table. This is an
-OR condition.
-
- My::Schema::Item->has_many('rels', 'My::Schema::Relationships',
- [ { 'foreign.LItemID' => 'self.ID' },
- { 'foreign.RItemID' => 'self.ID'} ]);
+A hashref, arrayref or coderef specifying a custom join expression. For
+more info see L<DBIx::Class::Relationship::Base/condition>.
=back
# in an Author class (where Author has_many Books)
# assuming related class is storing our PK in "author_id"
My::DBIC::Schema::Author->has_many(
- books =>
- 'My::DBIC::Schema::Book',
+ books =>
+ 'My::DBIC::Schema::Book',
'author_id'
);
# OR (same result)
My::DBIC::Schema::Author->has_many(
- books =>
- 'My::DBIC::Schema::Book',
+ books =>
+ 'My::DBIC::Schema::Book',
{ 'foreign.author_id' => 'self.id' },
);
-
+
# OR (similar result, assuming related_class is storing our PK, in "author")
# (the "author" is guessed at from "Author" in the class namespace)
My::DBIC::Schema::Author->has_many(
- books =>
- 'My::DBIC::Schema::Book',
+ books =>
+ 'My::DBIC::Schema::Book',
);
# Usage
- # resultset of Books belonging to author
+ # resultset of Books belonging to author
my $booklist = $author->books;
# resultset of Books belonging to author, restricted by author name
$author->add_to_books(\%col_data);
-Three methods are created when you create a has_many relationship. The first
-method is the expected accessor method, C<$accessor_name()>. The second is
-almost exactly the same as the accessor method but "_rs" is added to the end of
-the method name. This method works just like the normal accessor, except that
-it always returns a resultset, even in list context. The third method,
-named C<< add_to_$relname >>, will also be added to your Row items; this
-allows you to insert new related items, using the same mechanism as in
+Three methods are created when you create a has_many relationship.
+The first method is the expected accessor method, C<$accessor_name()>.
+The second is almost exactly the same as the accessor method but "_rs"
+is added to the end of the method name, eg C<$accessor_name_rs()>.
+This method works just like the normal accessor, except that it always
+returns a resultset, even in list context. The third method, named C<<
+add_to_$rel_name >>, will also be added to your Row items; this allows
+you to insert new related items, using the same mechanism as in
L<DBIx::Class::Relationship::Base/"create_related">.
If you delete an object in a class with a C<has_many> relationship, all
pass C<< cascade_copy => 0 >> in the C<$attr> hashref. The behaviour
defaults to C<< cascade_copy => 1 >>.
-See L<DBIx::Class::Relationship::Base> for documentation on relationship
-methods and valid relationship attributes. Also see L<DBIx::Class::ResultSet>
-for a L<list of standard resultset attributes|DBIx::Class::ResultSet/ATTRIBUTES>
-which can be assigned to relationships as well.
+See L<DBIx::Class::Relationship::Base/attributes> for documentation on
+relationship methods and valid relationship attributes. Also see
+L<DBIx::Class::ResultSet> for a L<list of standard resultset
+attributes|DBIx::Class::ResultSet/ATTRIBUTES> which can be assigned to
+relationships as well.
=head2 might_have
=over 4
-=item Arguments: $accessor_name, $related_class, $their_fk_column|\%cond|\@cond?, \%attr?
+=item Arguments: $accessor_name, $related_class, $their_fk_column|\%cond|\@cond|\&cond?, L<\%attrs?|DBIx::Class::ResultSet/ATTRIBUTES>
=back
defaults to using C<$accessor_name> as the foreign key in C<$related_class> to
resolve the join, unless C<$their_fk_column> specifies the foreign key
column in C<$related_class> or C<cond> specifies a reference to a join
-condition hash.
+condition.
=over
=item accessor_name
This argument is the name of the method you can call on a
-L<DBIx::Class::Row> object to retrieve the instance of the foreign
+L<Result|DBIx::Class::Manual::ResultClass> object to retrieve the instance of the foreign
class matching this relationship. This is often called the
C<relation(ship) name>.
=item cond
-A hashref where the keys are C<foreign.$their_fk_column> and
-the values are C<self.$matching_column>. This is useful for
-relations that are across multiple columns.
+A hashref, arrayref or coderef specifying a custom join expression. For
+more info see L<DBIx::Class::Relationship::Base/condition>.
=back
will have deleted/updated the related records or raised an exception
before DBIx::Class gets to perform the cascaded operation.
-See L<DBIx::Class::Relationship::Base> for documentation on relationship
-methods and valid relationship attributes. Also see L<DBIx::Class::ResultSet>
-for a L<list of standard resultset attributes|DBIx::Class::ResultSet/ATTRIBUTES>
-which can be assigned to relationships as well.
+See L<DBIx::Class::Relationship::Base/attributes> for documentation on
+relationship methods and valid relationship attributes. Also see
+L<DBIx::Class::ResultSet> for a L<list of standard resultset
+attributes|DBIx::Class::ResultSet/ATTRIBUTES> which can be assigned to
+relationships as well.
+
+Note that if you supply a condition on which to join, and the column in the
+current table allows nulls (i.e., has the C<is_nullable> attribute set to a
+true value), than C<might_have> will warn about this because it's naughty and
+you shouldn't do that. The warning will look something like:
+
+ "might_have/has_one" must not be on columns with is_nullable set to true (MySchema::SomeClass/key)
+
+If you must be naughty, you can suppress the warning by setting
+C<DBIC_DONT_VALIDATE_RELS> environment variable to a true value. Otherwise,
+you probably just meant to use C<DBIx::Class::Relationship/belongs_to>.
=head2 has_one
=over 4
-=item Arguments: $accessor_name, $related_class, $their_fk_column|\%cond|\@cond?, \%attr?
+=item Arguments: $accessor_name, $related_class, $their_fk_column|\%cond|\@cond|\&cond?, L<\%attrs?|DBIx::Class::ResultSet/ATTRIBUTES>
=back
defaults to using C<$accessor_name> as the foreign key in C<$related_class> to
resolve the join, unless C<$their_fk_column> specifies the foreign key
column in C<$related_class> or C<cond> specifies a reference to a join
-condition hash.
+condition.
=over
=item accessor_name
This argument is the name of the method you can call on a
-L<DBIx::Class::Row> object to retrieve the instance of the foreign
+L<Result|DBIx::Class::Manual::ResultClass> object to retrieve the instance of the foreign
class matching this relationship. This is often called the
C<relation(ship) name>.
=item cond
-A hashref where the keys are C<foreign.$their_fk_column> and
-the values are C<self.$matching_column>. This is useful for
-relations that are across multiple columns.
+A hashref, arrayref or coderef specifying a custom join expression. For
+more info see L<DBIx::Class::Relationship::Base/condition>.
=back
# Every book has exactly one ISBN
My::DBIC::Schema::Book->has_one(
- isbn =>
+ isbn =>
'My::DBIC::Schema::ISBN',
'book_id',
);
# OR (same result, assuming related_class stores our PK)
My::DBIC::Schema::Book->has_one(
- isbn =>
+ isbn =>
'My::DBIC::Schema::ISBN',
);
# OR (same result)
My::DBIC::Schema::Book->has_one(
- isbn =>
+ isbn =>
'My::DBIC::Schema::ISBN',
{ 'foreign.book_id' => 'self.id' },
);
C<might_have> is that C<has_one> uses an (ordinary) inner join,
whereas C<might_have> defaults to a left join.
-The has_one relationship should be used when a row in the table has exactly one
-related row in another table. If the related row might not exist in the foreign
-table, use the L<DBIx::Class::Relationship/might_have> relationship.
+The has_one relationship should be used when a row in the table must
+have exactly one related row in another table. If the related row
+might not exist in the foreign table, use the
+L<DBIx::Class::Relationship/might_have> relationship.
In the above example, each Book in the database is associated with exactly one
ISBN object.
-See L<DBIx::Class::Relationship::Base> for documentation on relationship
-methods and valid relationship attributes. Also see L<DBIx::Class::ResultSet>
-for a L<list of standard resultset attributes|DBIx::Class::ResultSet/ATTRIBUTES>
-which can be assigned to relationships as well.
+See L<DBIx::Class::Relationship::Base/attributes> for documentation on
+relationship methods and valid relationship attributes. Also see
+L<DBIx::Class::ResultSet> for a L<list of standard resultset
+attributes|DBIx::Class::ResultSet/ATTRIBUTES> which can be assigned to
+relationships as well.
+
+Note that if you supply a condition on which to join, if the column in the
+current table allows nulls (i.e., has the C<is_nullable> attribute set to a
+true value), than warnings might apply just as with
+L<DBIx::Class::Relationship/might_have>.
=head2 many_to_many
=over 4
-=item Arguments: $accessor_name, $link_rel_name, $foreign_rel_name, \%attr?
+=item Arguments: $accessor_name, $link_rel_name, $foreign_rel_name, L<\%attrs?|DBIx::Class::ResultSet/ATTRIBUTES>
=back
+C<many_to_many> is a I<Relationship bridge> which has a specific
+meaning in DBIx::Class, see the definition in the
+L<Glossary|DBIx::Class::Manual::Glossary/Relationship bridge>.
+
C<many_to_many> is not strictly a relationship in its own right. Instead, it is
a bridge between two resultsets which provide the same kind of convenience
-accessors as true relationships provide. Although the accessor will return a
-resultset or collection of objects just like has_many does, you cannot call
+accessors as true relationships provide. Although the accessor will return a
+resultset or collection of objects just like has_many does, you cannot call
C<related_resultset> and similar methods which operate on true relationships.
=over
=item accessor_name
This argument is the name of the method you can call on a
-L<DBIx::Class::Row> object to retrieve the rows matching this
+L<Result|DBIx::Class::Manual::ResultClass> object to retrieve the rows matching this
relationship.
On a many_to_many, unlike other relationships, this cannot be used in
will be created for the Role class for the C<actors> many_to_many
relationship.
-See L<DBIx::Class::Relationship::Base> for documentation on relationship
-methods and valid relationship attributes. Also see L<DBIx::Class::ResultSet>
-for a L<list of standard resultset attributes|DBIx::Class::ResultSet/ATTRIBUTES>
-which can be assigned to relationships as well.
-
-=cut
-
-1;
-
-=head1 AUTHORS
-
-see L<DBIx::Class>
+See L<DBIx::Class::Relationship::Base/attributes> for documentation on
+relationship methods and valid relationship attributes. Also see
+L<DBIx::Class::ResultSet> for a L<list of standard resultset
+attributes|DBIx::Class::ResultSet/ATTRIBUTES> which can be assigned to
+relationships as well.
-=head1 LICENSE
+=head1 FURTHER QUESTIONS?
-You may distribute this code under the same terms as Perl itself.
+Check the list of L<additional DBIC resources|DBIx::Class/GETTING HELP/SUPPORT>.
-=cut
+=head1 COPYRIGHT AND LICENSE
+This module is free software L<copyright|DBIx::Class/COPYRIGHT AND LICENSE>
+by the L<DBIx::Class (DBIC) authors|DBIx::Class/AUTHORS>. You can
+redistribute it and/or modify it under the same terms as the
+L<DBIx::Class library|DBIx::Class/COPYRIGHT AND LICENSE>.