Moose::Cookbook::Meta::Table_MetaclassTrait - Adding a "table" attribute as a metaclass trait |
Moose::Cookbook::Meta::Table_MetaclassTrait - Adding a ``table'' attribute as a metaclass trait
version 2.1605
# 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');
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.
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
the Moose::Cookbook::Extending::Debugging_BaseClassRole manpage, which shows how to
make a module like Moose.pm
itself, with sugar like has_table()
.
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.
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.
the Moose::Cookbook::Meta::Labeled_AttributeTrait manpage - Labels implemented via attribute traits =pod
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.
Moose::Cookbook::Meta::Table_MetaclassTrait - Adding a "table" attribute as a metaclass trait |