debian man page for dbix::class::helper::resultset::correlaterelationship

DBIx::Class::Helper::ResultSet::CorrelateRelationship(3pUser Contributed Perl DocumentatDBIx::Class::Helper::ResultSet::CorrelateRelationship(3pm)

NAME
       DBIx::Class::Helper::ResultSet::CorrelateRelationship - Easily correlate your ResultSets

VERSION
       version 2.013002

SYNOPSIS
	package MyApp::Schema::ResultSet::Author;

	use base 'DBIx::Class::ResultSet';

	__PACKAGE__->load_components(qw(Helper::ResultSet::CorrelateRelationship));

	sub with_book_count {
	  my $self = shift;

	  $self->search(undef, {
	    '+columns' => {
	      book_count => $self->correlate('book')->count_rs->as_query
	    }
	  });
	}

	1;

       And then elsewhere, like in a controller:

	my $rows = $schema->resultset('Author')->with_book_count->all;

DESCRIPTION
       Correlated queries are one of the coolest things I've learned about for SQL since my initial learning of SQL.  Unfortunately they are
       somewhat confusing.  DBIx::Class has supported doing them for a long time, but generally people don't think of them because they are so
       rare.  I won't go through all the details of how they work and cool things you can do with them, but here are a couple high level things
       you can use them for to save you time or effort.

       If you want to select a list of authors and counts of books for each author, you could use "group_by" and something like "COUNT(book.id)",
       but then you'd need to make your select list match your "group_by" and it would just be a hassle forever after that.  The "SYNOPSIS" is a
       perfect example of how to implement this.

       If you want to select a list of authors and two separate kinds of counts of books for each author, as far as I know, you must use a
       correlated subquery in DBIx::Class.  Here is an example of how you might do that:

	package MyApp::Schema::ResultSet::Author;

	use base 'DBIx::Class::ResultSet';

	__PACKAGE__->load_components(qw(Helper::ResultSet::CorrelateRelationship));

	sub with_good_book_count {
	  my $self = shift;

	  $self->search(undef, {
	    '+columns' => {
	      good_book_count => $self->correlate('books')->good->count_rs->as_query
	    }
	  });
	}

	sub with_bad_book_count {
	  my $self = shift;

	  $self->search(undef, {
	    '+columns' => {
	      bad_book_count => $self->correlate('books')->bad->count_rs->as_query
	    }
	  });
	}

	1;

       And then elsewhere, like in a controller:

	my $rows = $schema->resultset('Author')
	  ->with_bad_book_count
	  ->with_good_book_count
	  ->all;

       This assumes that the Book resultset has "good" and "bad" methods.

       See "NOTE" in DBIx::Class::Helper::ResultSet for a nice way to apply it to your entire schema.

METHODS
   correlate
	$rs->correlate($relationship_name)

       Correlate takes a single argument, a relationship for the invocant, and returns a resultset that can be used in the selector list.

AUTHOR
       Arthur Axel "fREW" Schmidt <frioux+cpan@gmail.com>

COPYRIGHT AND LICENSE
       This software is copyright (c) 2012 by Arthur Axel "fREW" Schmidt.

       This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

perl v5.14.2							    2012-06-18		DBIx::Class::Helper::ResultSet::CorrelateRelationship(3pm)