Moose::Cookbook::Meta:UserlContrMoose::Cookbook::Meta::Table_MetaclassTrait(3)NAMEMoose::Cookbook::Meta::Table_MetaclassTrait - Adding a "table"
attribute as a metaclass trait
VERSION
version 2.1005
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
AUTHOR
Moose is maintained by the Moose Cabal, along with the help of many
contributors. See "CABAL" in Moose and "CONTRIBUTORS" in Moose for
details.
COPYRIGHT AND LICENSE
This software is copyright (c) 2013 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.
perl v5.18.1Moose::Cookbook::Meta::Table_MetaclassTrait(3)
