Moose::Cookbook::Legacy::Table_ClassMetaclass

NAME
VERSION
SYNOPSIS
DESCRIPTION
THE METACLASS
CONCLUSION
SEE ALSO
AUTHORS
COPYRIGHT AND LICENSE

NAME

Moose::Cookbook::Legacy::Table_ClassMetaclass − Adding a “table” attribute to the metaclass

VERSION

version 2.2014

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

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.