Moose::Cookbook::Meta::Table_MetaclassTrait
Section: User Contributed Perl Documentation (3pm)
Updated: 2023-01-30
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NAME
Moose::Cookbook::Meta::Table_MetaclassTrait - Adding a "table" attribute as a metaclass trait
VERSION
version 2.2203
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
- •
-
Stevan Little <stevan@cpan.org>
- •
-
Dave Rolsky <autarch@urth.org>
- •
-
Jesse Luehrs <doy@cpan.org>
- •
-
Shawn M Moore <sartak@cpan.org>
- •
-
יובל קוג'מן (Yuval Kogman) <nothingmuch@woobling.org>
- •
-
Karen Etheridge <ether@cpan.org>
- •
-
Florian Ragwitz <rafl@debian.org>
- •
-
Hans Dieter Pearcey <hdp@cpan.org>
- •
-
Chris Prather <chris@prather.org>
- •
-
Matt S Trout <mstrout@cpan.org>
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.
Index
- NAME
-
- VERSION
-
- SYNOPSIS
-
- DESCRIPTION
-
- THE METACLASS TRAIT
-
- Using this Metaclass Trait in Practice
-
- RECIPE CAVEAT
-
- SEE ALSO
-
- AUTHORS
-
- COPYRIGHT AND LICENSE
-
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