Moose::Cookbook::Meta::Table_MetaclassTrait

NAME
VERSION
SYNOPSIS
DESCRIPTION
THE METACLASS TRAIT
RECIPE CAVEAT
SEE ALSO
AUTHORS
COPYRIGHT AND LICENSE

NAME

Moose::Cookbook::Meta::Table_MetaclassTrait − Adding a “table” attribute as a metaclass trait

VERSION

version 2.2014

SYNOPSIS

# in lib/MyApp/Meta/Class/Trait/HasTable.pm
package MyApp::Meta::Class::Trait::HasTable;
use Moose::Role;
Moose::Util::meta_class_alias(‘HasTable’);
has table => (
is => ‘rw’,
isa => ‘Str’,
);
# in lib/MyApp/User.pm
package MyApp::User;
use Moose −traits => ‘HasTable’;
__PACKAGE__−>meta−>table(‘User’);

DESCRIPTION

In this recipe, we’ll create a class metaclass trait which has a “table” attribute. This trait 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 TRAIT

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

Using this Metaclass Trait 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 apply the “MyApp::Meta::Class::Trait::HasTable” to its metaclass, this method call just works. If we want to be more careful, we can check that the class metaclass object has a “table” method:

$table = MyApp::User−>meta−>table
if MyApp::User−>meta−>can(‘table’);

In theory, this is not entirely correct, since the metaclass might be getting its “table” method from a different trait. In practice, you are unlikely to encounter this sort of problem.

RECIPE CAVEAT

This recipe doesn’t work when you paste it all into a single file. This is because the “use Moose −traits => ‘HasTable’;” line ends up being executed before the “table” attribute is defined.

When the two packages are separate files, this just works.

SEE ALSO

Moose::Cookbook::Meta::Labeled_AttributeTrait − Labels implemented via attribute traits =pod

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.