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Moose-2.1301-TRIAL
River stage four • 2950 direct dependents • 4061 total dependents
/ Moose::Cookbook::Legacy::Table_ClassMetaclass

NAME

Moose::Cookbook::Legacy::Table_ClassMetaclass - Adding a "table" attribute to the metaclass

VERSION

version 2.1301

SYNOPSIS

package MyApp::Meta::Class;
use Moose;
extends 'Moose::Meta::Class';

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

DESCRIPTION

WARNING: Subclassing metaclasses (as opposed to providing metaclass traits) is strongly discouraged. This recipe is provided solely for reference when encountering older code that does this.

In this recipe, we'll create a new metaclass which has a "table" attribute. This metaclass 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

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::Recipe2, which shows how to make a module like Moose.pm itself, with sugar like has_table().

Using this Metaclass 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 use MyApp::Meta::Class as its metaclass, this method call just works. If we want to be more careful, we can check the metaclass's class:

$table = MyApp::User->meta->table
    if MyApp::User->meta->isa('MyApp::Meta::Class');

CONCLUSION

Creating custom metaclass is trivial. Using it is a little harder, and is covered in other recipes. We will also talk about applying traits to a class metaclass, which is a more flexible and cooperative implementation.

SEE ALSO

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

Moose::Cookbook::Extending::Recipe2 - Acting like Moose.pm and providing sugar Moose-style

AUTHORS

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

  • Dave Rolsky <autarch@urth.org>

  • Jesse Luehrs <doy@tozt.net>

  • Shawn M Moore <code@sartak.org>

  • יובל קוג'מן (Yuval Kogman) <nothingmuch@woobling.org>

  • Karen Etheridge <ether@cpan.org>

  • Florian Ragwitz <rafl@debian.org>

  • Hans Dieter Pearcey <hdp@weftsoar.net>

  • Chris Prather <chris@prather.org>

  • 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.