NAME¶
DBIx::Class::Relationship::Base - Inter-table relationships
SYNOPSIS¶
__PACKAGE__->add_relationship(
spiders => 'My::DB::Result::Creatures',
sub {
my $args = shift;
return {
"$args->{foreign_alias}.id" => { -ident => "$args->{self_alias}.id" },
"$args->{foreign_alias}.type" => 'arachnid'
};
},
);
DESCRIPTION¶
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.
METHODS¶
add_relationship¶
- Arguments: $rel_name, $foreign_class, $condition, $attrs
__PACKAGE__->add_relationship('rel_name',
'Foreign::Class',
$condition, $attrs);
Create a custom relationship between one result source and another source,
indicated by its class name.
condition
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:
My::Schema::Author->has_many(
books => 'My::Schema::Book',
{ 'foreign.author_id' => 'self.id' }
);
A query like:
$author_rs->search_related('books')->next
will result in the following "JOIN" clause:
... FROM author me LEFT JOIN book books ON books.author_id = me.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".
Similarly:
My::Schema::Book->has_many(
editions => 'My::Schema::Edition',
{
'foreign.publisher_id' => 'self.publisher_id',
'foreign.type_id' => 'self.type_id',
}
);
...
$book_rs->search_related('editions')->next
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, the key-value pairs will be
"AND"ed in the resulting "JOIN" clause. An "OR"
can be achieved with an arrayref. For example a condition like:
My::Schema::Item->has_many(
related_item_links => My::Schema::Item::Links,
[
{ 'foreign.left_itemid' => 'self.id' },
{ 'foreign.right_itemid' => 'self.id' },
],
);
will translate to the following "JOIN" clause:
... FROM item me JOIN item_relations related_item_links ON
related_item_links.left_itemid = me.id
OR related_item_links.right_itemid = me.id ...
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:
My::Schema::Artist->has_many(
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" },
};
}
);
...
$artist_rs->search_related('cds_80s')->next;
will result in the "JOIN" clause:
... FROM artist me LEFT JOIN cd cds_80s ON
cds_80s.artist = me.artistid
AND cds_80s.year < ?
AND cds_80s.year > ?
with the bind values:
'1990', '1979'
"$args->{foreign_alias}" and "$args->{self_alias}" are
supplied the same values that would be otherwise substituted for
"foreign" and "self" in the simple hashref syntax case.
The coderef is expected to return a valid SQL::Abstract query-structure, just
like what one would supply as the first argument to "search" in
DBIx::Class::ResultSet. The return value will be passed directly to
SQL::Abstract and the resulting SQL will be used verbatim as the
"ON" clause of the "JOIN" statement associated with this
relationship.
While every coderef-based condition must return a valid "ON" clause,
it may elect to additionally return a simplified
optional join-free
condition consisting of a hashref with
all keys being fully qualified names
of columns declared on the corresponding result source. This boils
down to two scenarios:
- •
- When relationship resolution is invoked after
"$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 });
$artist->cds_80s->all;
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({});
$artist->set_from_related('cds_80s');
Will properly set the "$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:
$relationship_info->{cond}->({
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
});
attributes
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:
- join_type
- 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.
- \@columns
- 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
- \%column
- 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' } ],
});
- accessor
- 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.
- is_foreign_key_constraint
- 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.
- cascade_copy
- 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.
- cascade_delete
- 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.
- cascade_update
- 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.
- is_deferrable
- 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.
- add_fk_index
- 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.
register_relationship¶
- 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.
$relationship_accessor¶
- 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:
$self->search_related(@_)->delete
And returns the result of that.
add_to_$rel¶
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.
many_to_many
- Arguments: (\%col_data | $result), \%link_col_data?
- Return Value: $result
my $role = $schema->resultset('Role')->find(1);
$actor->add_to_roles($role);
# creates a My::DBIC::Schema::ActorRoles linking table result object
$actor->add_to_roles({ name => 'lead' }, { salary => 15_000_000 });
# creates a new My::DBIC::Schema::Role result object and the linking table
# object with an extra column in the link
Adds a linking table object. If the first argument is a hash reference, the
related object is created first with the column values in the hash. If an
object reference is given, just the linking table object is created. In either
case, any additional column values for the linking table object can be
specified in "\%link_col_data".
See "many_to_many" in DBIx::Class::Relationship for additional
details.
set_$rel¶
Currently only available for "many_to_many"
relationships.
- Arguments: (\@hashrefs_of_col_data | \@result_objs), $link_vals?
- Return Value: not defined
my $actor = $schema->resultset('Actor')->find(1);
my @roles = $schema->resultset('Role')->search({ role =>
{ '-in' => ['Fred', 'Barney'] } } );
$actor->set_roles(\@roles);
# 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.
remove_from_$rel¶
Currently only available for "many_to_many"
relationships.
- Arguments: $result
- Return Value: not defined
my $role = $schema->resultset('Role')->find(1);
$actor->remove_from_roles($role);
# 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.
FURTHER QUESTIONS?¶
Check the list of additional DBIC resources.
COPYRIGHT AND LICENSE¶
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.