# in lib/MyApp/Meta/Class/Trait/HasTable.pm
has table => (
is => 'rw',
isa => 'Str',
# in lib/MyApp/User.pm
use Moose -traits => 'HasTable';
DESCRIPTIONIn 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 TRAITThis 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 PracticeAccessing 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 CAVEATThis 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.
- Stevan Little <[email protected]>
- Dave Rolsky <[email protected]>
- Jesse Luehrs <[email protected]>
- Shawn M Moore <[email protected]>
- יובל קוג'מן (Yuval Kogman) <[email protected]>
- Karen Etheridge <[email protected]>
- Florian Ragwitz <[email protected]>
- Hans Dieter Pearcey <[email protected]>
- Chris Prather <[email protected]>
- Matt S Trout <[email protected]>
COPYRIGHT AND LICENSEThis 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.