Linux Certif

Toute la documentation sur la certification Linux LPI

Moose::Cookbook::Meta::Recipe4.3pm

NAME

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

SYNOPSIS

   package MyApp::Meta::Class;
   use Moose;
   extends 'Moose::Meta::Class';
 
   has table => (
       is  => 'rw',
       isa => 'Str',
   );
 
 

DESCRIPTION

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

AUTHOR

Dave Rolsky <autarch@urth.org>

COPYRIGHT AND LICENSE

Copyright 2006-2010 by Infinity Interactive, Inc.

<http://www.iinteractive.com>

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