Moose::Cookbook::Legacy::Table_ClassMetaclass

Section: User Contributed Perl Documentation (3)
Updated: 2018-05-16
Page Index
 

NAME

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

VERSION

version 2.2011  

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.


 

Index

NAME
VERSION
SYNOPSIS
DESCRIPTION
THE METACLASS
Using this Metaclass in Practice
CONCLUSION
SEE ALSO
AUTHORS
COPYRIGHT AND LICENSE
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