=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
$schema->resultset('Actor')->find({ id => 1})->roles();
=head1 DESCRIPTION
+The word I<Relationship> has a specific meaning in DBIx::Class, see
+the definition in the L<Glossary|DBIx::Class::Manual::Glossary/Relationship>.
+
This class provides methods to set up relationships between the tables
in your database model. Relationships are the most useful and powerful
technique that L<DBIx::Class> provides. To create efficient database queries,
All helper methods are called similar to the following template:
- __PACKAGE__->$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('relname', '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, $fk_column|\%cond|\@cond?, \%attr?
+=item Arguments: $accessor_name, $related_class, $our_fk_column|\%cond|\@cond|\$cond?, \%attrs?
=back
Creates a relationship where the calling class stores the foreign
-class's primary key in one (or more) of its columns. This relationship
-defaults to using C<$accessor_name> as the column in this class
-to resolve the join against the primary key from C<$related_class>,
-unless C<$fk_column> specifies the foreign key column in this class or
-C<cond> specifies a reference to a join condition hash.
+class's primary key in one (or more) of the calling class columns.
+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<$our_fk_column> specifies the foreign key column
+in this class or C<cond> specifies a reference to a join condition.
=over
This is the class name of the table referenced by the foreign key in
this class.
-=item fk_column
+=item our_fk_column
The column name on this class that contains the foreign key.
=item cond
-A hashref where the keys are C<foreign.$column_on_related_table> and
-the values are C<self.$foreign_key_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'
);
$book->get_column('author_id');
-If the relationship is optional -- i.e. the column containing the foreign key
-can be NULL -- then the belongs_to relationship does the right thing. Thus, in
-the example above C<$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 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->author >> would
+return C<undef>. However in this case you would probably want to set
+the L<join_type|DBIx::Class::Relationship/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:
# in a Book class (where Author has_many Books)
__PACKAGE__->belongs_to(
- author =>
+ author =>
'My::DBIC::Schema::Author',
- 'author',
+ 'author',
{ join_type => 'left' }
);
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
-methods and valid relationship attributes.
+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 has_many
=over 4
-=item Arguments: $accessor_name, $related_class, $foreign_key_column|\%cond|\@cond?, \%attr?
+=item Arguments: $accessor_name, $related_class, $their_fk_column|\%cond|\@cond|\&cond?, \%attrs?
=back
-Creates a one-to-many relationship, where the corresponding elements
-of the foreign class store the calling class's primary key in one (or
-more) of its columns. This relationship defaults to using the end of
-this classes namespace as the foreign key in C<$related_class> to
-resolve the join, unless C<$foreign_key_column> specifies the foreign
-key column in C<$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<$related_class> or C<cond>
+specifies a reference to a join condition.
=over
This is the class name of the table which contains a foreign key
column containing PK values of this class.
-=item foreign_key_column
+=item their_fk_column
The column name on the related class that contains the foreign key.
=item cond
-A hashref where the keys are C<foreign.$foreign_key_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<$accessor_name_rs()>.
+This method works just like the normal accessor, except that it always
+returns a resultset, even in list context. The third method, named C<<
+add_to_$relname >>, 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.
+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, $foreign_key_column|\%cond|\@cond?, \%attr?
+=item Arguments: $accessor_name, $related_class, $their_fk_column|\%cond|\@cond|\&cond?, \%attrs?
=back
Creates an optional one-to-one relationship with a class. This relationship
defaults to using C<$accessor_name> as the foreign key in C<$related_class> to
-resolve the join, unless C<$foreign_key_column> specifies the foreign key
+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
This is the class name of the table which contains a foreign key
column containing PK values of this class.
-=item foreign_key_column
+=item their_fk_column
The column name on the related class that contains the foreign key.
=item cond
-A hashref where the keys are C<foreign.$column_on_related_table> and
-the values are C<self.$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.
+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, $foreign_key_column|\%cond|\@cond?, \%attr?
+=item Arguments: $accessor_name, $related_class, $their_fk_column|\%cond|\@cond|\&cond?, \%attrs?
=back
Creates a one-to-one relationship with a class. This relationship
defaults to using C<$accessor_name> as the foreign key in C<$related_class> to
-resolve the join, unless C<$foreign_key_column> specifies the foreign key
+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
This is the class name of the table which contains a foreign key
column containing PK values of this class.
-=item foreign_key_column
+=item their_fk_column
The column name on the related class that contains the foreign key.
=item cond
-A hashref where the keys are C<foreign.$column_on_related_table> and
-the values are C<self.$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.
+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, \%attrs?
=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
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.
+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.
=cut
projects / dbsrgits/DBIx-Class.git / blobdiff