=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, $attrs);
-
+ __PACKAGE__->$method_name('relname', 'Foreign::Class', \%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>.
+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
-attrubutes that are allowed in the C<$attrs> argument.
+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, $our_fk_column|\%cond|\@cond?, \%attrs?
=back
Creates a relationship where the calling class stores the foreign
-class's primary key in one (or more) of its columns. This relationship
-defaults to using C<$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<$our_fk_column> specifies the foreign key column
+in this class or C<cond> specifies a reference to a join condition hash.
=over
This is the class name of the table referenced by the foreign key in
this class.
-=item fk_column
+=item our_fk_column
The column name on this class that contains the foreign key.
=item cond
A hashref where the keys are C<foreign.$column_on_related_table> and
-the values are C<self.$foreign_key_column>. This is useful for
+the values are C<self.$our_fk_column>. This is useful for
relations that are across multiple columns.
=back
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.
+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, $their_fk_column|\%cond|\@cond?, \%attrs?
=back
-Creates a one-to-many relationship, where the corresponding elements
-of the foreign class store the calling class's primary key in one (or
-more) of its columns. This relationship defaults to using the end of
-this classes namespace as the foreign key in C<$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<$related_class> or C<cond>
+specifies a reference to a join condition hash.
=over
This is the class name of the table which contains a foreign key
column containing PK values of this class.
-=item foreign_key_column
+=item their_fk_column
The column name on the related class that contains the foreign key.
=item cond
-A hashref where the keys are C<foreign.$foreign_key_column> and
+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.
'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(
defaults to C<< cascade_copy => 1 >>.
See L<DBIx::Class::Relationship::Base> for documentation on relationship
-methods and valid relationship attributes.
+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, $their_fk_column|\%cond|\@cond?, \%attrs?
=back
Creates an optional one-to-one relationship with a class. This relationship
defaults to using C<$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.
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.$column_on_related_table> and
+A hashref where the keys are C<foreign.$their_fk_column> and
the values are C<self.$matching_column>. This is useful for
relations that are across multiple columns.
before DBIx::Class gets to perform the cascaded operation.
See L<DBIx::Class::Relationship::Base> for documentation on relationship
-methods and valid relationship attributes.
+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.
+
+ "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, $foreign_key_column|\%cond|\@cond?, \%attr?
+=item Arguments: $accessor_name, $related_class, $their_fk_column|\%cond|\@cond?, \%attrs?
=back
Creates a one-to-one relationship with a class. This relationship
defaults to using C<$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.
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.$column_on_related_table> and
+A hashref where the keys are C<foreign.$their_fk_column> and
the values are C<self.$matching_column>. This is useful for
relations that are across multiple columns.
ISBN object.
See L<DBIx::Class::Relationship::Base> for documentation on relationship
-methods and valid relationship attributes.
+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
relationship.
See L<DBIx::Class::Relationship::Base> for documentation on relationship
-methods and valid relationship attributes.
+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
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