The London Perl and Raku Workshop takes place on 26th Oct 2024. If your company depends on Perl, please consider sponsoring and/or attending.


DBIx::Class::Relationship::Base - Inter-table relationships


    spiders => 'My::DB::Result::Creatures',
    sub {
      my $args = shift;
      return {
        "$args->{foreign_alias}.id"   => { -ident => "$args->{self_alias}.id" },
        "$args->{foreign_alias}.type" => 'arachnid'


This class provides methods to describe the relationships between the tables in your database model. These are the "bare bones" relationships methods, for predefined ones, look in DBIx::Class::Relationship.



Arguments: $rel_name, $foreign_class, $condition, $attrs
                                $condition, $attrs);

Create a custom relationship between one result source and another source, indicated by its class name.


The condition argument describes the ON clause of the JOIN expression used to connect the two sources when creating SQL queries.

Simple equality

To create simple equality joins, supply a hashref containing the remote table column name as the key(s) prefixed by 'foreign.', and the corresponding local table column name as the value(s) prefixed by 'self.'. Both foreign and self are pseudo aliases and must be entered literally. They will be replaced with the actual correct table alias when the SQL is produced.

For example given:

    books => 'My::Schema::Book',
    { 'foreign.author_id' => '' }

A query like:


will result in the following JOIN clause:

  ... FROM author me LEFT JOIN book books ON books.author_id = ...

This describes a relationship between the Author table and the Book table where the Book table has a column author_id containing the ID value of the Author.


    editions => 'My::Schema::Edition',
      'foreign.publisher_id' => 'self.publisher_id',
      'foreign.type_id'      => 'self.type_id',



will result in the JOIN clause:

  ... FROM book me
      LEFT JOIN edition editions ON
           editions.publisher_id = me.publisher_id
       AND editions.type_id = me.type_id ...

This describes the relationship from Book to Edition, where the Edition table refers to a publisher and a type (e.g. "paperback"):

Multiple groups of simple equality conditions

As is the default in SQL::Abstract::Classic, the key-value pairs will be ANDed in the resulting JOIN clause. An OR can be achieved with an arrayref. For example a condition like:

    related_item_links => My::Schema::Item::Links,
      { 'foreign.left_itemid'  => '' },
      { 'foreign.right_itemid' => '' },

will translate to the following JOIN clause:

 ... FROM item me JOIN item_relations related_item_links ON
         related_item_links.left_itemid =
      OR related_item_links.right_itemid = ...

This describes the relationship from Item to Item::Links, where Item::Links is a many-to-many linking table, linking items back to themselves in a peer fashion (without a "parent-child" designation)

Custom join conditions

  NOTE: The custom join condition specification mechanism is capable of
  generating JOIN clauses of virtually unlimited complexity. This may limit
  your ability to traverse some of the more involved relationship chains the
  way you expect, *and* may bring your RDBMS to its knees. Exercise care
  when declaring relationships as described here.

To specify joins which describe more than a simple equality of column values, the custom join condition coderef syntax can be used. For example:

    cds_80s => 'My::Schema::CD',
    sub {
      my $args = shift;

      return {
        "$args->{foreign_alias}.artist" => { -ident => "$args->{self_alias}.artistid" },
        "$args->{foreign_alias}.year"   => { '>', "1979", '<', "1990" },



will result in the JOIN clause:

  ... FROM artist me LEFT JOIN cd cds_80s ON
        cds_80s.artist = me.artistid
    AND cds_80s.year < ?
    AND cds_80s.year > ?

with the bind values:

   '1990', '1979'

$args->{foreign_alias} and $args->{self_alias} are supplied the same values that would be otherwise substituted for foreign and self in the simple hashref syntax case.

The coderef is expected to return a valid SQL::Abstract::Classic query-structure, just like what one would supply as the first argument to "search" in DBIx::Class::ResultSet. The return value will be passed directly to DBIx::Class::SQLMaker and the resulting SQL will be used verbatim as the ON clause of the JOIN statement associated with this relationship.

While every coderef-based condition must return a valid ON clause, it may elect to additionally return a simplified optional join-free condition consisting of a hashref with all keys being fully qualified names of columns declared on the corresponding result source. This boils down to two scenarios:

  • When relationship resolution is invoked after $result->$rel_name, as opposed to $rs->related_resultset($rel_name), the $result object is passed to the coderef as $args->{self_result_object}.

  • Alternatively when the user-space invokes resolution via $result->set_from_related( $rel_name => $foreign_values_or_object ), the corresponding data is passed to the coderef as $args->{foreign_values}, always in the form of a hashref. If a foreign result object is supplied (which is valid usage of "set_from_related"), its values will be extracted into hashref form by calling get_columns.

Note that the above scenarios are mutually exclusive, that is you will be supplied none or only one of self_result_object and foreign_values. In other words if you define your condition coderef as:

  sub {
    my $args = shift;

    return (
        "$args->{foreign_alias}.artist" => { -ident => "$args->{self_alias}.artistid" },
        "$args->{foreign_alias}.year"   => { '>', "1979", '<', "1990" },
      ! $args->{self_result_object} ? () : {
        "$args->{foreign_alias}.artist" => $args->{self_result_object}->artistid,
        "$args->{foreign_alias}.year"   => { '>', "1979", '<', "1990" },
      ! $args->{foreign_values} ? () : {
        "$args->{self_alias}.artistid" => $args->{foreign_values}{artist},

Then this code:

    my $artist = $schema->resultset("Artist")->find({ id => 4 });

Can skip a JOIN altogether and instead produce:

    SELECT cds_80s.cdid, cds_80s.artist, cds_80s.title, cds_80s.year, cds_80s.genreid, cds_80s.single_track
      FROM cd cds_80s
      WHERE cds_80s.artist = ?
        AND cds_80s.year < ?
        AND cds_80s.year > ?

With the bind values:

    '4', '1990', '1979'

While this code:

    my $cd = $schema->resultset("CD")->search({ artist => 1 }, { rows => 1 })->single;
    my $artist = $schema->resultset("Artist")->new({});

Will properly set the $artist->artistid field of this new object to 1

Note that in order to be able to use "set_from_related" (and by extension $result->create_related), the returned join free condition must contain only plain values/deflatable objects. For instance the year constraint in the above example prevents the relationship from being used to create related objects using $artst->create_related( cds_80s => { title => 'blah' } ) (an exception will be thrown).

In order to allow the user to go truly crazy when generating a custom ON clause, the $args hashref passed to the subroutine contains some extra metadata. Currently the supplied coderef is executed as:

    self_resultsource   => The resultsource instance on which rel_name is registered
    rel_name            => The relationship name (does *NOT* always match foreign_alias)

    self_alias          => The alias of the invoking resultset
    foreign_alias       => The alias of the to-be-joined resultset (does *NOT* always match rel_name)

    # only one of these (or none at all) will ever be supplied to aid in the
    # construction of a join-free condition

    self_result_object  => The invocant *object* itself in case of a call like
                           $result_object->$rel_name( ... )

    foreign_values      => A *hashref* of related data: may be passed in directly or
                           derived via ->get_columns() from a related object in case of
                           $result_object->set_from_related( $rel_name, $foreign_result_object )

    # deprecated inconsistent names, will be forever available for legacy code
    self_rowobj         => Old deprecated slot for self_result_object
    foreign_relname     => Old deprecated slot for rel_name


The standard ResultSet attributes may be used as relationship attributes. In particular, the 'where' attribute is useful for filtering relationships:

     __PACKAGE__->has_many( 'valid_users', 'MyApp::Schema::User',
        { 'foreign.user_id' => 'self.user_id' },
        { where => { valid => 1 } }

The following attributes are also valid:


Explicitly specifies the type of join to use in the relationship. Any SQL join type is valid, e.g. LEFT or RIGHT. It will be placed in the SQL command immediately before JOIN.

proxy => $column | \@columns | \%column

The 'proxy' attribute can be used to retrieve values, and to perform updates if the relationship has 'cascade_update' set. The 'might_have' and 'has_one' relationships have this set by default; if you want a proxy to update across a 'belongs_to' relationship, you must set the attribute yourself.


An arrayref containing a list of accessors in the foreign class to create in the main class. If, for example, you do the following:

  MyApp::Schema::CD->might_have(liner_notes => 'MyApp::Schema::LinerNotes',
    undef, {
      proxy => [ qw/notes/ ],

Then, assuming MyApp::Schema::LinerNotes has an accessor named notes, you can do:

  my $cd = MyApp::Schema::CD->find(1);
  $cd->notes('Notes go here'); # set notes -- LinerNotes object is
                               # created if it doesn't exist

For a 'belongs_to relationship, note the 'cascade_update':

  MyApp::Schema::Track->belongs_to( cd => 'MyApp::Schema::CD', 'cd,
      { proxy => ['title'], cascade_update => 1 }
  $track->title('New Title');
  $track->update; # updates title in CD

A hashref where each key is the accessor you want installed in the main class, and its value is the name of the original in the foreign class.

  MyApp::Schema::Track->belongs_to( cd => 'MyApp::Schema::CD', 'cd', {
      proxy => { cd_title => 'title' },

This will create an accessor named cd_title on the $track result object.

NOTE: you can pass a nested struct too, for example:

  MyApp::Schema::Track->belongs_to( cd => 'MyApp::Schema::CD', 'cd', {
    proxy => [ 'year', { cd_title => 'title' } ],

Specifies the type of accessor that should be created for the relationship. Valid values are single (for when there is only a single related object), multi (when there can be many), and filter (for when there is a single related object, but you also want the relationship accessor to double as a column accessor). For multi accessors, an add_to_* method is also created, which calls create_related for the relationship.


If you are using SQL::Translator to create SQL for you and you find that it is creating constraints where it shouldn't, or not creating them where it should, set this attribute to a true or false value to override the detection of when to create constraints.


If cascade_copy is true on a has_many relationship for an object, then when you copy the object all the related objects will be copied too. To turn this behaviour off, pass cascade_copy => 0 in the $attr hashref.

The behaviour defaults to cascade_copy => 1 for has_many relationships.


By default, DBIx::Class cascades deletes across has_many, has_one and might_have relationships. You can disable this behaviour on a per-relationship basis by supplying cascade_delete => 0 in the relationship attributes.

The cascaded operations are performed after the requested delete, 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.


By default, DBIx::Class cascades updates across has_one and might_have relationships. You can disable this behaviour on a per-relationship basis by supplying cascade_update => 0 in the relationship attributes.

The belongs_to relationship does not update across relationships by default, so if you have a 'proxy' attribute on a belongs_to and want to use 'update' on it, you must set cascade_update => 1.

This is not a RDMS style cascade update - it purely means that when an object has update called on it, all the related objects also have update called. It will not change foreign keys automatically - you must arrange to do this yourself.

on_delete / on_update

If you are using SQL::Translator to create SQL for you, you can use these attributes to explicitly set the desired ON DELETE or ON UPDATE constraint type. If not supplied the SQLT parser will attempt to infer the constraint type by interrogating the attributes of the opposite relationship. For any 'multi' relationship with cascade_delete => 1, the corresponding belongs_to relationship will be created with an ON DELETE CASCADE constraint. For any relationship bearing cascade_copy => 1 the resulting belongs_to constraint will be ON UPDATE CASCADE. If you wish to disable this autodetection, and just use the RDBMS' default constraint type, pass on_delete => undef or on_delete => '', and the same for on_update respectively.


Tells SQL::Translator that the foreign key constraint it creates should be deferrable. In other words, the user may request that the constraint be ignored until the end of the transaction. Currently, only the PostgreSQL producer actually supports this.


Tells SQL::Translator to add an index for this constraint. Can also be specified globally in the args to "deploy" in DBIx::Class::Schema or "create_ddl_dir" in DBIx::Class::Schema. Default is on, set to 0 to disable.


Arguments: $rel_name, $rel_info

Registers a relationship on the class. This is called internally by DBIx::Class::ResultSourceProxy to set up Accessors and Proxies.

Arguments: $rel_name
Return Value: $related_resultset
  $rs = $cd->related_resultset('artist');

Returns a DBIx::Class::ResultSet for the relationship named $rel_name.


Arguments: none
Return Value: $result | $related_resultset | undef
  # These pairs do the same thing
  $result = $cd->related_resultset('artist')->single;  # has_one relationship
  $result = $cd->artist;
  $rs = $cd->related_resultset('tracks');           # has_many relationship
  $rs = $cd->tracks;

This is the recommended way to traverse through relationships, based on the "accessor" name given in the relationship definition.

This will return either a Result or a ResultSet, depending on if the relationship is single (returns only one row) or multi (returns many rows). The method may also return undef if the relationship doesn't exist for this instance (like in the case of might_have relationships).

Arguments: $rel_name, $cond?, \%attrs?
Return Value: $resultset (scalar context) | @result_objs (list context)

Run a search on a related resultset. The search will be restricted to the results represented by the DBIx::Class::ResultSet it was called upon.

See "search_related" in DBIx::Class::ResultSet for more information.

This method works exactly the same as search_related, except that it guarantees a resultset, even in list context.

Arguments: $rel_name, $cond?, \%attrs?
Return Value: $count

Returns the count of all the rows in the related resultset, restricted by the current result or where conditions.

Arguments: $rel_name, \%col_data
Return Value: $result

Create a new result object of the related foreign class. It will magically set any foreign key columns of the new object to the related primary key columns of the source object for you. The newly created result will not be saved into your storage until you call "insert" in DBIx::Class::Row on it.

Arguments: $rel_name, \%col_data
Return Value: $result
  my $result = $obj->create_related($rel_name, \%col_data);

Creates a new result object, similarly to new_related, and also inserts the result's data into your storage medium. See the distinction between create and new in DBIx::Class::ResultSet for details.

Arguments: $rel_name, \%col_data | @pk_values, { key => $unique_constraint, %attrs }?
Return Value: $result | undef
  my $result = $obj->find_related($rel_name, \%col_data);

Attempt to find a related object using its primary key or unique constraints. See "find" in DBIx::Class::ResultSet for details.

Arguments: $rel_name, \%col_data, { key => $unique_constraint, %attrs }?
Return Value: $result

Find a result object of a related class. See "find_or_new" in DBIx::Class::ResultSet for details.

Arguments: $rel_name, \%col_data, { key => $unique_constraint, %attrs }?
Return Value: $result

Find or create a result object of a related class. See "find_or_create" in DBIx::Class::ResultSet for details.

Arguments: $rel_name, \%col_data, { key => $unique_constraint, %attrs }?
Return Value: $result

Update or create a result object of a related class. See "update_or_create" in DBIx::Class::ResultSet for details.

Arguments: $rel_name, $result
Return Value: not defined
  $book->set_from_related('author', $author_obj);
  $book->author($author_obj);                      ## same thing

Set column values on the current object, using related values from the given related object. This is used to associate previously separate objects, for example, to set the correct author for a book, find the Author object, then call set_from_related on the book.

This is called internally when you pass existing objects as values to "create" in DBIx::Class::ResultSet, or pass an object to a belongs_to accessor.

The columns are only set in the local copy of the object, call update to update them in the storage.

Arguments: $rel_name, $result
Return Value: not defined
  $book->update_from_related('author', $author_obj);

The same as "set_from_related", but the changes are immediately updated in storage.

Arguments: $rel_name, $cond?, \%attrs?
Return Value: $underlying_storage_rv

Delete any related row, subject to the given conditions. Internally, this calls:


And returns the result of that.


Currently only available for has_many, many_to_many and 'multi' type relationships.

has_many / multi

Arguments: \%col_data
Return Value: $result

Creates/inserts a new result object. Internally, this calls:

  $self->create_related($rel, @_)

And returns the result of that.


Return Value: $result
  my $role = $schema->resultset('Role')->find(1);
      # creates a My::DBIC::Schema::ActorRoles linking table result object

  $actor->add_to_roles({ name => 'lead' }, { salary => 15_000_000 });
      # creates a new My::DBIC::Schema::Role result object and the linking table
      # object with an extra column in the link

Adds a linking table object. If the first argument is a hash reference, the related object is created first with the column values in the hash. If an object reference is given, just the linking table object is created. In either case, any additional column values for the linking table object can be specified in \%link_col_data.

See "many_to_many" in DBIx::Class::Relationship for additional details.


Currently only available for many_to_many relationships.

Return Value: not defined
  my $actor = $schema->resultset('Actor')->find(1);
  my @roles = $schema->resultset('Role')->search({ role =>
     { '-in' => ['Fred', 'Barney'] } } );

     # Replaces all of $actor's previous roles with the two named

  $actor->set_roles(\@roles, { salary => 15_000_000 });
     # Sets a column in the link table for all roles

Replace all the related objects with the given reference to a list of objects. This does a delete on the link table resultset to remove the association between the current object and all related objects, then calls add_to_$rel repeatedly to link all the new objects.

Note that this means that this method will not delete any objects in the table on the right side of the relation, merely that it will delete the link between them.

Due to a mistake in the original implementation of this method, it will also accept a list of objects or hash references. This is deprecated and will be removed in a future version.


Currently only available for many_to_many relationships.

Arguments: $result
Return Value: not defined
  my $role = $schema->resultset('Role')->find(1);
      # removes $role's My::DBIC::Schema::ActorRoles linking table result object

Removes the link between the current object and the related object. Note that the related object itself won't be deleted unless you call ->delete() on it. This method just removes the link between the two objects.


Check the list of additional DBIC resources.


This module is free software copyright by the DBIx::Class (DBIC) authors. You can redistribute it and/or modify it under the same terms as the DBIx::Class library.