NAME

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

VERSION

version 2.2201

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.

AUTHORS

Stevan Little <stevan@cpan.org>
Dave Rolsky <autarch@urth.org>
Jesse Luehrs <doy@cpan.org>
Shawn M Moore <sartak@cpan.org>
יובל קוג'מן (Yuval Kogman) <nothingmuch@woobling.org>
Karen Etheridge <ether@cpan.org>
Florian Ragwitz <rafl@debian.org>
Hans Dieter Pearcey <hdp@cpan.org>
Chris Prather <chris@prather.org>
Matt S Trout <mstrout@cpan.org>

COPYRIGHT AND LICENSE

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