X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=lib%2FDBIx%2FClass%2FRelationship.pm;h=770953fa1663cc1ded0b602c0f43f039d90e74ab;hb=cddf2c632219902fca385b7fb4e307de2fd3ec36;hp=d7d1675c489a953c83cf236fdfd0aac4771babb5;hpb=07037f89d4d9bf97c59a2c083de74f669521da47;p=dbsrgits%2FDBIx-Class-Historic.git diff --git a/lib/DBIx/Class/Relationship.pm b/lib/DBIx/Class/Relationship.pm index d7d1675..770953f 100644 --- a/lib/DBIx/Class/Relationship.pm +++ b/lib/DBIx/Class/Relationship.pm @@ -3,20 +3,16 @@ package DBIx::Class::Relationship; use strict; use warnings; -use base qw/DBIx::Class Class::Data::Inheritable/; +use base qw/DBIx::Class/; __PACKAGE__->load_own_components(qw/ - HasMany - HasOne - BelongsTo + Helpers Accessor CascadeActions ProxyMethods Base /); -__PACKAGE__->mk_classdata('_relationships', { } ); - =head1 NAME DBIx::Class::Relationship - Inter-table relationships @@ -25,20 +21,152 @@ DBIx::Class::Relationship - Inter-table relationships =head1 DESCRIPTION -This class handles relationships between the tables in your database -model. It allows your to set up relationships, and to perform joins -on searches. +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 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 +L objects that represent the items +of your table. From L 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 = $schema->resultset('Author')->find({ + Name => 'Fred', + })->books->search_related('prices', { + Price => { '<=' => '5.00' }, + }); + +will produce a query something like: + + SELECT * FROM Author me + LEFT JOIN Books books ON books.author = me.id + LEFT JOIN Prices prices ON prices.book = books.id + WHERE prices.Price <= 5.00 + +all without needing multiple fetches. + +Only the helper methods for setting up standard relationship types +are documented here. For the basic, lower-level methods, see +L. =head1 METHODS -=over 4 +All helper methods take the following arguments: + + __PACKAGE__>$method_name('relname', 'Foreign::Class', $cond, $attrs); + +Both C<$cond> and C<$attrs> are optional. Pass C for C<$cond> if +you want to use the default value for it, but still want to set C<$attrs>. +See L for a list of valid attributes. + +=head2 belongs_to + + # in a Book class (where Author has many Books) + My::DBIC::Schema::Book->belongs_to(author => 'Author'); + my $author_obj = $obj->author; + $obj->author($new_author_obj); + +Creates a relationship where the calling class stores the foreign class's +primary key in one (or more) of its columns. If $cond is a column name +instead of a join condition hash, that is used as the name of the column +holding the foreign key. If $cond is not given, the relname is used as +the column name. + +NOTE: If you are used to L relationships, this is the equivalent +of C. + +=head2 has_many + + # in an Author class (where Author has many Books) + My::DBIC::Schema::Author->has_many(books => 'Book', 'author'); + my $booklist = $obj->books; + my $booklist = $obj->books({ + name => { LIKE => '%macaroni%' }, + { prefetch => [qw/book/], + }); + my @book_objs = $obj->books; + + $obj->add_to_books(\%col_data); + +Creates a one-to-many relationship, where the corresponding elements of the +foreign class store the calling class's primary key in one (or more) of its +columns. You should pass the name of the column in the foreign class as the +$cond argument, or specify a complete join condition. + +If you delete an object in a class with a C relationship, all +related objects will be deleted as well. However, any database-level +cascade or restrict will take precedence. + +=head2 might_have + + My::DBIC::Schema::Author->might_have(psuedonym => 'Psuedonyms'); + my $pname = $obj->psuedonym; # to get the Psuedonym object + +Creates an optional one-to-one relationship with a class, where the foreign +class stores our primary key in one of its columns. Defaults to the primary +key of the foreign class unless $cond specifies a column or join condition. + +If you update or delete an object in a class with a C +relationship, the related object will be updated or deleted as well. +Any database-level update or delete constraints will override this behaviour. + +=head2 has_one + + My::DBIC::Schema::Book->has_one(isbn => ISBN); + my $isbn_obj = $obj->isbn; + +Creates a one-to-one relationship with another class. This is just like +C, except the implication is that the other object is always +present. The only difference between C and C is that +C uses an (ordinary) inner join, whereas C uses a +left join. + + +=head2 many_to_many + + My::DBIC::Schema::Actor->many_to_many( roles => 'actor_roles', 'Roles' ); + + ... + + my @role_objs = $actor->roles; + +Creates an accessor 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. =cut 1; -=back - =head1 AUTHORS Matt S. Trout