Section: User Contributed Perl Documentation (3)
Moose::Cookbook::Meta::Table_MetaclassTrait - Adding a "table" attribute as a metaclass trait
# in lib/MyApp/Meta/Class/Trait/HasTable.pm
has table => (
is => 'rw',
isa => 'Str',
# in lib/MyApp/User.pm
use Moose -traits => 'HasTable';
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
, 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
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.
Moose::Cookbook::Meta::Labeled_AttributeTrait - Labels implemented via
Stevan Little <firstname.lastname@example.org>
Dave Rolsky <email@example.com>
Jesse Luehrs <firstname.lastname@example.org>
Shawn M Moore <email@example.com>
יובל קוג'מן (Yuval Kogman) <firstname.lastname@example.org>
Karen Etheridge <email@example.com>
Florian Ragwitz <firstname.lastname@example.org>
Hans Dieter Pearcey <email@example.com>
Chris Prather <firstname.lastname@example.org>
Matt S Trout <email@example.com>
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.