DBIx::Class::RelationsUser3Contributed Perl DocumeDBIx::Class::Relationship(3)NAME
DBIx::Class::Relationship - Inter-table relationships
SYNOPSIS
## Creating relationships
MyApp::Schema::Actor->has_many('actorroles' => 'MyApp::Schema::ActorRole',
'actor');
MyApp::Schema::Role->has_many('actorroles' => 'MyApp::Schema::ActorRole',
'role');
MyApp::Schema::ActorRole->belongs_to('role' => 'MyApp::Schema::Role');
MyApp::Schema::ActorRole->belongs_to('actor' => 'MyApp::Schema::Actor');
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();
$schema->resultset('Role')->find({ id => 1 })->actorroles->search_related('actor', { Name => 'Fred' });
$schema->resultset('Actor')->add_to_roles({ Name => 'Sherlock Holmes'});
See DBIx::Class::Manual::Cookbook for more.
DESCRIPTION
The word Relationship has a specific meaning in DBIx::Class, see the
definition in the Glossary.
This class provides methods to set up relationships between the tables
in your database model. Relationships are the most useful and powerful
technique that DBIx::Class provides. To create efficient database
queries, create relationships between any and all tables that have
something in common, for example if you have a table Authors:
ID | Name | Age
------------------
1 | Fred | 30
2 | Joe | 32
and a table Books:
ID | Author | Name
--------------------
1 | 1 | Rulers of the universe
2 | 1 | Rulers of the galaxy
Then without relationships, the method of getting all books by Fred
goes like this:
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:
my $fredsbooks = $schema->resultset('Author')->find({ Name => 'Fred' })->books;
Each relationship sets up an accessor method on the "Row" in
DBIx::Class::Manual::Glossary objects that represent the items of your
table. From "ResultSet" in DBIx::Class::Manual::Glossary objects, the
relationships can be searched using the "search_related" method. In
list context, each returns a list of Row objects for the related class,
in scalar context, a new ResultSet representing the joined tables is
returned. Thus, the calls can be chained to produce complex queries.
Since the database is not actually queried until you attempt to
retrieve the data for an actual item, no time is wasted producing them.
my $cheapfredbooks = $schema->resultset('Author')->find({
Name => 'Fred',
})->books->search_related('prices', {
Price => { '<=' => '5.00' },
});
will produce a query something like:
SELECT * FROM Author me
LEFT JOIN Books books ON books.author = me.id
LEFT JOIN Prices prices ON prices.book = books.id
WHERE prices.Price <= 5.00
all without needing multiple fetches.
Only the helper methods for setting up standard relationship types are
documented here. For the basic, lower-level methods, and a description
of all the useful *_related methods that you get for free, see
DBIx::Class::Relationship::Base.
METHODS
All helper methods are called similar to the following template:
__PACKAGE__->$method_name('relname', 'Foreign::Class', \%cond|\@cond|\&cond?, \%attrs?);
Both "cond" and "attrs" are optional. Pass "undef" for "cond" if you
want to use the default value for it, but still want to set "attrs".
See "condition" in DBIx::Class::Relationship::Base for full
documentation on definition of the "cond" argument.
See "attributes" in DBIx::Class::Relationship::Base for documentation
on the attributes that are allowed in the "attrs" argument.
belongs_to
Arguments: $accessor_name, $related_class,
$our_fk_column|\%cond|\@cond|\$cond?, \%attrs?
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 $accessor_name as the column name
in this class to resolve the join against the primary key from
$related_class, unless $our_fk_column specifies the foreign key column
in this class or "cond" specifies a reference to a join condition.
accessor_name
This argument is the name of the method you can call on a
DBIx::Class::Row object to retrieve the instance of the foreign
class matching this relationship. This is often called the
"relation(ship) name".
Use this accessor_name in "join" in DBIx::Class::ResultSet or
"prefetch" in DBIx::Class::ResultSet to join to the foreign table
indicated by this relationship.
related_class
This is the class name of the table referenced by the foreign key
in this class.
our_fk_column
The column name on this class that contains the foreign key.
OR
cond
A hashref, arrayref or coderef specifying a custom join expression.
For more info see "condition" in DBIx::Class::Relationship.
# in a Book class (where Author has many Books)
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:
$book->get_column('author_id');
If the relationship is optional -- i.e. the column containing the
foreign key can be NULL -- then the belongs_to relationship does the
right thing. Thus, in the example above "$obj->author" would return
"undef". However in this case you would probably want to set the
join_type attribute so that a "LEFT JOIN" is done, which makes complex
resultsets involving "join" or "prefetch" 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' }
);
Cascading deletes are off by default on a "belongs_to" relationship. To
turn them on, pass "cascade_delete => 1" in the $attr hashref.
By default, DBIC will return undef and avoid querying the database if a
"belongs_to" accessor is called when any part of the foreign key IS
NULL. To disable this behavior, pass "undef_on_null_fk => 0" in the
"\%attrs" hashref.
NOTE: If you are used to Class::DBI relationships, this is the
equivalent of "has_a".
See "attributes" in DBIx::Class::Relationship::Base for documentation
on relationship methods and valid relationship attributes. Also see
DBIx::Class::ResultSet for a list of standard resultset attributes
which can be assigned to relationships as well.
has_many
Arguments: $accessor_name, $related_class,
$their_fk_column|\%cond|\@cond|\&cond?, \%attrs?
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 "LEFT JOIN"). This relationship
defaults to using the end of this classes namespace as the foreign key
in $related_class to resolve the join, unless $their_fk_column
specifies the foreign key column in $related_class or "cond" specifies
a reference to a join condition.
accessor_name
This argument is the name of the method you can call on a
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
"relation(ship) name".
Use this accessor_name in "join" in DBIx::Class::ResultSet or
"prefetch" in DBIx::Class::ResultSet to join to the foreign table
indicated by this relationship.
related_class
This is the class name of the table which contains a foreign key
column containing PK values of this class.
their_fk_column
The column name on the related class that contains the foreign key.
OR
cond
A hashref, arrayref or coderef specifying a custom join
expression. For more info see "condition" in
DBIx::Class::Relationship.
# 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',
'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/],
});
# 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;
# create a new book for this author, the relation fields are auto-filled
$author->create_related('books', \%col_data);
# alternative method for the above
$author->add_to_books(\%col_data);
Three methods are created when you create a has_many relationship. The
first method is the expected accessor method, "$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 "$accessor_name_rs()". This
method works just like the normal accessor, except that it always
returns a resultset, even in list context. The third method, named
"add_to_$relname", will also be added to your Row items; this allows
you to insert new related items, using the same mechanism as in
"create_related" in DBIx::Class::Relationship::Base.
If you delete an object in a class with a "has_many" relationship, all
the related objects will be deleted as well. To turn this behaviour
off, pass "cascade_delete => 0" in the $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 "has_many" relationship, all
the related objects will be copied as well. To turn this behaviour off,
pass "cascade_copy => 0" in the $attr hashref. The behaviour defaults
to "cascade_copy => 1".
See "attributes" in DBIx::Class::Relationship::Base for documentation
on relationship methods and valid relationship attributes. Also see
DBIx::Class::ResultSet for a list of standard resultset attributes
which can be assigned to relationships as well.
might_have
Arguments: $accessor_name, $related_class,
$their_fk_column|\%cond|\@cond|\&cond?, \%attrs?
Creates an optional one-to-one relationship with a class. This
relationship defaults to using $accessor_name as the foreign key in
$related_class to resolve the join, unless $their_fk_column specifies
the foreign key column in $related_class or "cond" specifies a
reference to a join condition.
accessor_name
This argument is the name of the method you can call on a
DBIx::Class::Row object to retrieve the instance of the foreign
class matching this relationship. This is often called the
"relation(ship) name".
Use this accessor_name in "join" in DBIx::Class::ResultSet or
"prefetch" in DBIx::Class::ResultSet to join to the foreign table
indicated by this relationship.
related_class
This is the class name of the table which contains a foreign key
column containing PK values of this class.
their_fk_column
The column name on the related class that contains the foreign key.
OR
cond
A hashref, arrayref or coderef specifying a custom join
expression. For more info see "condition" in
DBIx::Class::Relationship.
# 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 "might_have"
relationship, the related object will be updated or deleted as well. To
turn off this behavior, add "cascade_delete => 0" to the $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.
See "attributes" in DBIx::Class::Relationship::Base for documentation
on relationship methods and valid relationship attributes. Also see
DBIx::Class::ResultSet for a list of standard 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 "is_nullable" attribute
set to a true value), than "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
"DBIC_DONT_VALIDATE_RELS" environment variable to a true value.
Otherwise, you probably just meant to use
"DBIx::Class::Relationship/belongs_to".
has_one
Arguments: $accessor_name, $related_class,
$their_fk_column|\%cond|\@cond|\&cond?, \%attrs?
Creates a one-to-one relationship with a class. This relationship
defaults to using $accessor_name as the foreign key in $related_class
to resolve the join, unless $their_fk_column specifies the foreign key
column in $related_class or "cond" specifies a reference to a join
condition.
accessor_name
This argument is the name of the method you can call on a
DBIx::Class::Row object to retrieve the instance of the foreign
class matching this relationship. This is often called the
"relation(ship) name".
Use this accessor_name in "join" in DBIx::Class::ResultSet or
"prefetch" in DBIx::Class::ResultSet to join to the foreign table
indicated by this relationship.
related_class
This is the class name of the table which contains a foreign key
column containing PK values of this class.
their_fk_column
The column name on the related class that contains the foreign key.
OR
cond
A hashref, arrayref or coderef specifying a custom join
expression. For more info see "condition" in
DBIx::Class::Relationship.
# 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
"might_have", except the implication is that the other object is always
present. The only difference between "has_one" and "might_have" is that
"has_one" uses an (ordinary) inner join, whereas "might_have" defaults
to a left join.
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 "might_have" in
DBIx::Class::Relationship relationship.
In the above example, each Book in the database is associated with
exactly one ISBN object.
See "attributes" in DBIx::Class::Relationship::Base for documentation
on relationship methods and valid relationship attributes. Also see
DBIx::Class::ResultSet for a list of standard 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 "is_nullable" attribute
set to a true value), than warnings might apply just as with
"might_have" in DBIx::Class::Relationship.
many_to_many
Arguments: $accessor_name, $link_rel_name, $foreign_rel_name, \%attrs?
"many_to_many" is a Relationship bridge which has a specific meaning in
DBIx::Class, see the definition in the Glossary.
"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 "related_resultset" and similar methods
which operate on true relationships.
accessor_name
This argument is the name of the method you can call on a
DBIx::Class::Row object to retrieve the rows matching this
relationship.
On a many_to_many, unlike other relationships, this cannot be used
in "search" in DBIx::Class::ResultSet to join tables. Use the
relations bridged across instead.
link_rel_name
This is the accessor_name from the has_many relationship we are
bridging from.
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).
To create a many_to_many relationship from Actor to Role:
My::DBIC::Schema::Actor->has_many( actor_roles =>
'My::DBIC::Schema::ActorRoles',
'actor' );
My::DBIC::Schema::ActorRoles->belongs_to( role =>
'My::DBIC::Schema::Role' );
My::DBIC::Schema::ActorRoles->belongs_to( actor =>
'My::DBIC::Schema::Actor' );
My::DBIC::Schema::Actor->many_to_many( roles => 'actor_roles',
'role' );
And, for the reverse relationship, from Role to Actor:
My::DBIC::Schema::Role->has_many( actor_roles =>
'My::DBIC::Schema::ActorRoles',
'role' );
My::DBIC::Schema::Role->many_to_many( actors => 'actor_roles', 'actor' );
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 $link_rel_name parameter is the name of the
accessor for the has_many relationship from this table to the link
table, and the $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 Actor class will have 3 many_to_many accessor
methods set: "roles", "add_to_roles", "set_roles", and similarly named
accessors will be created for the Role class for the "actors"
many_to_many relationship.
See "attributes" in DBIx::Class::Relationship::Base for documentation
on relationship methods and valid relationship attributes. Also see
DBIx::Class::ResultSet for a list of standard resultset attributes
which can be assigned to relationships as well.
AUTHORS
see DBIx::Class
LICENSE
You may distribute this code under the same terms as Perl itself.
perl v5.12.5 2011-07-26 DBIx::Class::Relationship(3)
