=head1 SYNOPSIS
+ ## Creating relationships
MyDB::Schema::Actor->has_many('actorroles' => 'MyDB::Schema::ActorRole',
'actor');
MyDB::Schema::Role->has_many('actorroles' => 'MyDB::Schema::ActorRole',
MyDB::Schema::Role->many_to_many('actors' => 'actorroles', 'actor');
MyDB::Schema::Actor->many_to_many('roles' => 'actorroles', 'role');
- $schema->resultset('Actor')->roles();
- $schema->resultset('Role')->search_related('actors', { Name => 'Fred' });
- $schema->resultset('ActorRole')->add_to_roles({ Name => 'Sherlock Holmes'});
+ ## Using relationships
+ $schema->resultset('Actor')->find({ id => 1})->roles();
+ $schema->resultset('Role')->find({ id => 1 })->actorroles->search_related('actor', { Name => 'Fred' });
+ $schema->resultset('Actor')->add_to_roles({ Name => 'Sherlock Holmes'});
See L<DBIx::Class::Manual::Cookbook> for more.
=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 $fred = $schema->resultset('Author')->find({ Name => 'Fred' });
my $fredsbooks = $schema->resultset('Book')->search({ Author => $fred->ID });
+
With a has_many relationship called "books" on Author (see below for details),
we can do this instead:
=head1 METHODS
-All helper methods take the following arguments:
+All helper methods are called similar to the following template:
+
+ __PACKAGE__->$method_name('relname', 'Foreign::Class', \%cond | \@cond, \%attrs);
- __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>.
-See L<DBIx::Class::Relationship::Base> for a list of valid attributes.
+you want to use the default value for it, but still want to set C<\%attrs>.
+
+See L<DBIx::Class::Relationship::Base> for documentation on the
+attributes that are allowed in the C<\%attrs> argument.
+
=head2 belongs_to
=over 4
-=item Arguments: $accessor_name, $related_class, $foreign_key_column?, $attr?
+=item Arguments: $accessor_name, $related_class, $our_fk_column|\%cond|\@cond?, \%attrs?
+
+=back
+
+Creates a relationship where the calling class stores the foreign
+class's primary key in one (or more) of the calling class columns.
+This relationship defaults to using C<$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 hash.
+
+=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
+class matching this relationship. This is often called the
+C<relation(ship) name>.
+
+Use this accessor_name in L<DBIx::Class::ResultSet/join>
+or L<DBIx::Class::ResultSet/prefetch> to join to the foreign table
+indicated by this relationship.
+
+=item related_class
+
+This is the class name of the table referenced by the foreign key in
+this class.
+
+=item our_fk_column
+
+The column name on this class that contains the foreign key.
+
+OR
+
+=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.
=back
+
# in a Book class (where Author has many Books)
- My::DBIC::Schema::Book->belongs_to(author => 'My::DBIC::Schema::Author');
- my $author_obj = $obj->author;
- $obj->author($new_author_obj);
+ My::DBIC::Schema::Book->belongs_to(
+ author =>
+ 'My::DBIC::Schema::Author',
+ 'author_id'
+ );
+
+ # OR (same result)
+ My::DBIC::Schema::Book->belongs_to(
+ author =>
+ 'My::DBIC::Schema::Author',
+ { 'foreign.author_id' => 'self.author_id' }
+ );
+
+ # OR (similar result but uglier accessor name)
+ My::DBIC::Schema::Book->belongs_to(
+ author_id =>
+ 'My::DBIC::Schema::Author'
+ );
+
+ # Usage
+ my $author_obj = $book->author; # get author object
+ $book->author( $new_author_obj ); # set author object
+ $book->author_id(); # get the plain id
+
+ # To retrieve the plain id if you used the ugly version:
+ $book->get_column('author_id');
-Creates a relationship where the calling class stores the foreign class's
-primary key in one (or more) of its columns. If C<$cond> is a column name
-instead of a join condition hash, it is used as the name of the foreign key
-column in the calling class. If C<$cond> is not given, C<$accessor_name> is
-used as the column name.
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
operations work correctly. The modified declaration is shown below:
# in a Book class (where Author has_many Books)
- __PACKAGE__->belongs_to(author => 'My::DBIC::Schema::Author',
- 'author', {join_type => 'left'});
+ __PACKAGE__->belongs_to(
+ author =>
+ 'My::DBIC::Schema::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 $attr hashref.
+By default, DBIC will return undef and avoid querying the database if a
+C<belongs_to> accessor is called when any part of the foreign key IS NULL. To
+disable this behavior, pass C<< undef_on_null_fk => 0 >> in the C<$attr>
+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. 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?, $attr?
+=item Arguments: $accessor_name, $related_class, $their_fk_column|\%cond|\@cond?, \%attrs?
+
+=back
+
+Creates a one-to-many relationship where the foreign class refers to
+this class's primary key. This relationship refers to zero or more
+records in the foreign table (e.g. a C<LEFT JOIN>). This relationship
+defaults to using the end of this classes namespace as the foreign key
+in C<$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 hash.
+
+=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
+C<relation(ship) name>.
+
+Use this accessor_name in L<DBIx::Class::ResultSet/join>
+or L<DBIx::Class::ResultSet/prefetch> to join to the foreign table
+indicated by this relationship.
+
+=item related_class
+
+This is the class name of the table which contains a foreign key
+column containing PK values of this class.
+
+=item their_fk_column
+
+The column name on the related class that contains the foreign key.
+
+OR
+
+=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'} ]);
=back
# in an Author class (where Author has_many Books)
- My::DBIC::Schema::Author->has_many(books => 'My::DBIC::Schema::Book', 'author');
- my $booklist = $obj->books;
- my $booklist = $obj->books({
+ # assuming related class is storing our PK in "author_id"
+ My::DBIC::Schema::Author->has_many(
+ books =>
+ 'My::DBIC::Schema::Book',
+ 'author_id'
+ );
+
+ # OR (same result)
+ My::DBIC::Schema::Author->has_many(
+ 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',
+ );
+
+
+ # Usage
+ # resultset of Books belonging to author
+ my $booklist = $author->books;
+
+ # resultset of Books belonging to author, restricted by author name
+ my $booklist = $author->books({
name => { LIKE => '%macaroni%' },
{ prefetch => [qw/book/],
});
- my @book_objs = $obj->books;
- my $books_rs = $obj->books;
+
+ # array of Book objects belonging to author
+ my @book_objs = $author->books;
+
+ # force resultset even in list context
+ my $books_rs = $author->books;
( $books_rs ) = $obj->books_rs;
- $obj->add_to_books(\%col_data);
+ # create a new book for this author, the relation fields are auto-filled
+ $author->create_related('books', \%col_data);
+ # alternative method for the above
+ $author->add_to_books(\%col_data);
-Creates a one-to-many relationship, where the corresponding elements of the
-foreign class store the calling class's primary key in one (or more) of its
-columns. You should pass the name of the column in the foreign class as the
-C<$cond> argument, or specify a complete join condition.
Three methods are created when you create a has_many relationship. The first
method is the expected accessor method, C<$accessor_name()>. The second is
almost exactly the same as the accessor method but "_rs" is added to the end of
the method name. This method works just like the normal accessor, except that
-it returns a resultset no matter what, even in list context. The third method,
-named C<< add_to_<relname> >>, will also be added to your Row items; this
+it always returns a resultset, even in list context. The third method,
+named C<< add_to_$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
the related objects will be deleted as well. To turn this behaviour off,
-pass C<< cascade_delete => 0 >> in the C<$attr> hashref. However, any
-database-level cascade or restrict will take precedence over a
-DBIx-Class-based cascading delete.
+pass C<< cascade_delete => 0 >> in the C<$attr> hashref.
+
+The cascaded operations are performed after the requested delete or
+update, so if your database has a constraint on the relationship, it
+will have deleted/updated the related records or raised an exception
+before DBIx::Class gets to perform the cascaded operation.
+
+If you copy an object in a class with a C<has_many> relationship, all
+the related objects will be copied as well. To turn this behaviour off,
+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.
=head2 might_have
=over 4
-=item Arguments: $accessor_name, $related_class, $join_condition?, $attr?
+=item Arguments: $accessor_name, $related_class, $their_fk_column|\%cond|\@cond?, \%attrs?
=back
- My::DBIC::Schema::Author->might_have(pseudonym =>
- 'My::DBIC::Schema::Pseudonym');
+Creates an optional one-to-one relationship with a class. This relationship
+defaults to using C<$accessor_name> as the foreign key in C<$related_class> to
+resolve the join, unless C<$their_fk_column> specifies the foreign key
+column in C<$related_class> or C<cond> specifies a reference to a join
+condition hash.
- my $pname = $obj->pseudonym; # to get the Pseudonym object
+=over
-Creates an optional one-to-one relationship with a class. This relationship
-defaults to using the relationship name as the foreign key in C<$related_class>
-to resolve the join, unless C<$join_condition> specifies a column in
-C<$related_class> or a join condition hash reference.
+=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
+class matching this relationship. This is often called the
+C<relation(ship) name>.
+
+Use this accessor_name in L<DBIx::Class::ResultSet/join>
+or L<DBIx::Class::ResultSet/prefetch> to join to the foreign table
+indicated by this relationship.
+
+=item related_class
+
+This is the class name of the table which contains a foreign key
+column containing PK values of this class.
+
+=item their_fk_column
+
+The column name on the related class that contains the foreign key.
+
+OR
+
+=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.
+
+=back
+
+ # Author may have an entry in the pseudonym table
+ My::DBIC::Schema::Author->might_have(
+ pseudonym =>
+ 'My::DBIC::Schema::Pseudonym',
+ 'author_id',
+ );
+
+ # OR (same result, assuming the related_class stores our PK)
+ My::DBIC::Schema::Author->might_have(
+ pseudonym =>
+ 'My::DBIC::Schema::Pseudonym',
+ );
+
+ # OR (same result)
+ My::DBIC::Schema::Author->might_have(
+ pseudonym =>
+ 'My::DBIC::Schema::Pseudonym',
+ { 'foreign.author_id' => 'self.id' },
+ );
+
+ # Usage
+ my $pname = $author->pseudonym; # to get the Pseudonym object
If you update or delete an object in a class with a C<might_have>
relationship, the related object will be updated or deleted as well. To
turn off this behavior, add C<< cascade_delete => 0 >> to the C<$attr>
-hashref. Any database-level update or delete constraints will override
-this behavior.
+hashref.
+
+The cascaded operations are performed after the requested delete or
+update, so if your database has a constraint on the relationship, it
+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.
+
+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 C<might_have> will warn about this because it's naughty and
+you shouldn't do that.
-In the above example
+ "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 want to use C<DBIx::Class::Relationship/belongs_to>.
=head2 has_one
=over 4
-=item Arguments: $accessor_name, $related_class_name, $join_condition?, $attr?
+=item Arguments: $accessor_name, $related_class, $their_fk_column|\%cond|\@cond?, \%attrs?
=back
- My::DBIC::Schema::Book->has_one(isbn => 'My::DBIC::Schema::ISBN');
+Creates a one-to-one relationship with a class. This relationship
+defaults to using C<$accessor_name> as the foreign key in C<$related_class> to
+resolve the join, unless C<$their_fk_column> specifies the foreign key
+column in C<$related_class> or C<cond> specifies a reference to a join
+condition hash.
+
+=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
+class matching this relationship. This is often called the
+C<relation(ship) name>.
+
+Use this accessor_name in L<DBIx::Class::ResultSet/join>
+or L<DBIx::Class::ResultSet/prefetch> to join to the foreign table
+indicated by this relationship.
- my $isbn_obj = $obj->isbn; # to get the ISBN object
+=item related_class
-Creates a one-to-one relationship with another class. This is just like
-C<might_have>, except the implication is that the other object is always
-present. The only difference between C<has_one> and C<might_have> is that
-C<has_one> uses an (ordinary) inner join, whereas C<might_have> uses a
-left join.
+This is the class name of the table which contains a foreign key
+column containing PK values of this class.
+
+=item their_fk_column
+
+The column name on the related class that contains the foreign key.
+
+OR
+
+=item cond
+
+A hashref where the keys are C<foreign.$their_fk_column> and
+the values are C<self.$matching_column>. This is useful for
+relations that are across multiple columns.
+
+=back
+
+ # Every book has exactly one ISBN
+ My::DBIC::Schema::Book->has_one(
+ isbn =>
+ 'My::DBIC::Schema::ISBN',
+ 'book_id',
+ );
+
+ # OR (same result, assuming related_class stores our PK)
+ My::DBIC::Schema::Book->has_one(
+ isbn =>
+ 'My::DBIC::Schema::ISBN',
+ );
+
+ # OR (same result)
+ My::DBIC::Schema::Book->has_one(
+ isbn =>
+ 'My::DBIC::Schema::ISBN',
+ { 'foreign.book_id' => 'self.id' },
+ );
+
+ # Usage
+ my $isbn_obj = $book->isbn; # to get the ISBN object
+
+Creates a one-to-one relationship with another class. This is just
+like C<might_have>, except the implication is that the other object is
+always present. The only difference between C<has_one> and
+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
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.
+
+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:
+=item Arguments: $accessor_name, $link_rel_name, $foreign_rel_name, \%attrs?
-=over 4
+=back
-=item C<$accessor_name>: The name of the new many_to_many accessor,
+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>.
-=item C<$link_rel_name>: The accessor name of the has_many relationship from
- the current table to the link table,
+C<many_to_many> is not strictly a relationship in its own right. Instead, it is
+a bridge between two resultsets which provide the same kind of convenience
+accessors as true relationships provide. Although the accessor will return a
+resultset or collection of objects just like has_many does, you cannot call
+C<related_resultset> and similar methods which operate on true relationships.
-=item C<$foreign_rel_name>: The accessor name for the belongs_to relationship
- from the link table to the foreign table
+=over
-=item C<$attr>: A hash of relationship attributes for the created many_to_many
- relationship accessors to use on the C<$foreign_rel_name>.
+=item accessor_name
-=back
+This argument is the name of the method you can call on a
+L<DBIx::Class::Row> object to retrieve the rows matching this
+relationship.
+
+On a many_to_many, unlike other relationships, this cannot be used in
+L<DBIx::Class::ResultSet/search> to join tables. Use the relations
+bridged across instead.
+
+=item link_rel_name
+
+This is the accessor_name from the has_many relationship we are
+bridging from.
+
+=item foreign_rel_name
+
+This is the accessor_name of the belongs_to relationship in the link
+table that we are bridging across (which gives us the table we are
+bridging to).
=back
My::DBIC::Schema::Role->many_to_many( actors => 'actor_roles', 'actor' );
-Creates accessors bridging two relationships; not strictly a relationship in
-its own right, although the accessor will return a resultset or collection of
-objects just as a has_many would.
+To add a role for your actor, and fill in the year of the role in the
+actor_roles table:
+
+ $actor->add_to_roles($role, { year => 1995 });
+
+In the above example, ActorRoles is the link table class, and Role is the
+foreign class. The C<$link_rel_name> parameter is the name of the accessor for
+the has_many relationship from this table to the link table, and the
+C<$foreign_rel_name> parameter is the accessor for the belongs_to relationship
+from the link table to the foreign table.
To use many_to_many, existing relationships from the original table to the link
table, and from the link table to the end table must already exist, these
relation names are then used in the many_to_many call.
-In the above example, the Role class will have 3 many_to_many accessor methods
-set: C<$roles>, C<$add_to_roles>, C<$set_roles>, and similarly named accessors
-will be created for the Actor class. See L<DBIx::Class::Relationship::Base> for
-more information.
+In the above example, the Actor class will have 3 many_to_many accessor methods
+set: C<roles>, C<add_to_roles>, C<set_roles>, and similarly named accessors
+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
=head1 AUTHORS
-Matt S. Trout <mst@shadowcatsystems.co.uk>
+see L<DBIx::Class>
=head1 LICENSE
projects / dbsrgits/DBIx-Class.git / blobdiff