moose::cookbook::meta::recipe5(3) [osx man page]

Moose::Cookbook::Meta::Recipe5(3)			User Contributed Perl Documentation			 Moose::Cookbook::Meta::Recipe5(3)

NAME

       Moose::Cookbook::Meta::Recipe5 - The "table" attribute as a metaclass trait

VERSION

       version 2.0205

SYNOPSIS

	 package MyApp::Meta::Class::Trait::HasTable;
	 use Moose::Role;

	 has table => (
	     is  => 'rw',
	     isa => 'Str',
	 );

	 package Moose::Meta::Class::Custom::Trait::HasTable;
	 sub register_implementation { 'MyApp::Meta::Class::Trait::HasTable' }

	 package MyApp::User;
	 use Moose -traits => 'HasTable';

	 __PACKAGE__->meta->table('User');

DESCRIPTION

       This recipe takes the metaclass table attribute from Moose::Cookbook::Meta::Recipe4 and implements it as a metaclass trait. Traits are just
       roles, as we saw in Moose::Cookbook::Meta::Recipe3.

       The advantage of using traits is that it's easy to combine multiple traits, whereas combining multiple metaclass subclasses requires
       creating yet another subclass. With traits, Moose takes care of applying them to your metaclass.

   Using this Metaclass Trait in Practice
       Once this trait has been applied to a metaclass, it looks exactly like the example we saw in Moose::Cookbook::Meta::Recipe4:

	 my $table = MyApp::User->meta->table;

	 # the safe version
	 $table = MyApp::User->meta->table
	     if MyApp::User->meta->meta->can('does')
		and MyApp::User->meta->meta->does('MyApp::Meta::Class');

       The safe version is a little complicated. We have to check that the metaclass object's metaclass has a "does" method, in which case we can
       ask if the the metaclass does a given role.

       It's simpler to just write:

	 $table = MyApp::User->meta->table
	     if MyApp::User->meta->can('table');

       In theory, this is a little less correct, since the metaclass might be getting its "table" method from a different role. In practice, you
       are unlikely to encounter this sort of problem.

SEE ALSO

       Moose::Cookbook::Meta::Recipe3 - Labels implemented via attribute traits

       Moose::Cookbook::Meta::Recipe4 - Adding a "table" attribute to the metaclass

AUTHOR

       Stevan Little <stevan@iinteractive.com>

COPYRIGHT AND LICENSE

       This software is copyright (c) 2011 by Infinity Interactive, Inc..

       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 v5.12.5							    2011-09-06					 Moose::Cookbook::Meta::Recipe5(3)

Moose::Cookbook::Meta::Table_MetaclassTrait(3)		User Contributed Perl Documentation	    Moose::Cookbook::Meta::Table_MetaclassTrait(3)

NAME

       Moose::Cookbook::Meta::Table_MetaclassTrait - Adding a "table" attribute as a metaclass trait

VERSION

       version 2.1202

SYNOPSIS

	 # in lib/MyApp/Meta/Class/Trait/HasTable.pm
	 package MyApp::Meta::Class::Trait::HasTable;
	 use Moose::Role;
	 Moose::Util::meta_class_alias('HasTable');

	 has table => (
	     is  => 'rw',
	     isa => 'Str',
	 );

	 # in lib/MyApp/User.pm
	 package MyApp::User;
	 use Moose -traits => 'HasTable';

	 __PACKAGE__->meta->table('User');

DESCRIPTION

       In this recipe, we'll create a class metaclass trait which has a "table" attribute. This trait is for classes associated with a DBMS table,
       as one might do for an ORM.

       In this example, the table name is just a string, but in a real ORM the table might be an object describing the table.

THE METACLASS TRAIT

       This really is as simple as the recipe "SYNOPSIS" shows. The trick is getting your classes to use this metaclass, and providing some sort
       of sugar for declaring the table. This is covered in Moose::Cookbook::Extending::Debugging_BaseClassRole, which shows how to make a module
       like "Moose.pm" itself, with sugar like "has_table()".

   Using this Metaclass Trait in Practice
       Accessing this new "table" attribute is quite simple. Given a class named "MyApp::User", we could simply write the following:

	 my $table = MyApp::User->meta->table;

       As long as "MyApp::User" has arranged to apply the "MyApp::Meta::Class::Trait::HasTable" to its metaclass, this method call just works. If
       we want to be more careful, we can check that the class metaclass object has a "table" method:

	 $table = MyApp::User->meta->table
	     if MyApp::User->meta->can('table');

       In theory, this is not entirely correct, since the metaclass might be getting its "table" method from a different trait. In practice, you
       are unlikely to encounter this sort of problem.

RECIPE CAVEAT

       This recipe doesn't work when you paste it all into a single file. This is because the "use Moose -traits => 'HasTable';" line ends up
       being executed before the "table" attribute is defined.

       When the two packages are separate files, this just works.

SEE ALSO

       Moose::Cookbook::Meta::Labeled_AttributeTrait - Labels implemented via attribute traits

AUTHORS

       o   Stevan Little <stevan.little@iinteractive.com>

       o   Dave Rolsky <autarch@urth.org>

       o   Jesse Luehrs <doy@tozt.net>

       o   Shawn M Moore <code@sartak.org>

       o   XXXX XXX'XX (Yuval Kogman) <nothingmuch@woobling.org>

       o   Karen Etheridge <ether@cpan.org>

       o   Florian Ragwitz <rafl@debian.org>

       o   Hans Dieter Pearcey <hdp@weftsoar.net>

       o   Chris Prather <chris@prather.org>

       o   Matt S Trout <mst@shadowcat.co.uk>

COPYRIGHT AND LICENSE

       This software is copyright (c) 2006 by Infinity Interactive, Inc..

       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 v5.18.2							    2014-01-19			    Moose::Cookbook::Meta::Table_MetaclassTrait(3)