Fey::Meta::Attribute::FromSelect - An attribute metaclass for SELECT-based attributes

version 0.43

  package MyApp::Song;

  has average_rating => (
      metaclass   => 'FromSelect',
      is          => 'ro',
      isa         => 'Float',
      select      => $select,
      bind_params => sub { $_[0]->song_id() },
  );

This attribute metaclass allows you to set an attribute's default based on a SELECT query and optional bound parameters. This is a fairly common need when writing ORM-based classes.

This metaclass accepts two additional parameters in addition to the normal Moose attribute options.

* select

This must do the Fey::Role::SQL::ReturnsData role. It is required.

* bind_params

This must be a subroutine reference, which when called will return an array of bind parameters for the query. This subref will be called as a method on the object which has the attribute. This is an optional parameter.

Note that this metaclass overrides any value you provide for "default" with a subroutine that executes the query and gets the value it returns.

This class adds a few methods to those provided by Moose::Meta::Attribute:

Returns the query object associated with this attribute.

Returns the bind_params subroutine reference associated with this attribute, if any.

By default, the SELECT is expected to return just a single row with one column. However, if you set the type of the attribute to ArrayRef (or a subtype), then the select can return multiple rows, still with a single column.

Dave Rolsky <autarch@urth.org>

This software is copyright (c) 2011 by Dave Rolsky.

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