From: Jess Robinson Date: Tue, 21 Mar 2006 00:25:14 +0000 (+0000) Subject: ddddocs! X-Git-Tag: v0.06000~52 X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=commitdiff_plain;h=bc1171c38d8bb5cc2d007a3892c121b882ca4012;p=dbsrgits%2FDBIx-Class.git ddddocs! --- diff --git a/lib/DBIx/Class/Relationship.pm b/lib/DBIx/Class/Relationship.pm index 68a223e..0ee14aa 100644 --- a/lib/DBIx/Class/Relationship.pm +++ b/lib/DBIx/Class/Relationship.pm @@ -21,8 +21,54 @@ DBIx::Class::Relationship - Inter-table relationships =head1 DESCRIPTION -This class handles relationships between the tables in your database -model. It allows you to set up relationships and perform joins on them. +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