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Code Editor : Table_MetaclassTrait.pod

# PODNAME: Moose::Cookbook::Meta::Table_MetaclassTrait
# ABSTRACT: Adding a "table" attribute as a metaclass trait

__END__

=pod

=encoding UTF-8

=head1 NAME

Moose::Cookbook::Meta::Table_MetaclassTrait - Adding a "table" attribute as a metaclass trait

=head1 VERSION

version 2.2014

=head1 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');

=head1 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.

=begin testing-SETUP

BEGIN {
  package MyApp::Meta::Class::Trait::HasTable;
  use Moose::Role;
  Moose::Util::meta_class_alias('HasTable');

has table => (
      is  => 'rw',
      isa => 'Str',
  );
}

=end testing-SETUP

=head1 THE METACLASS TRAIT

This really is as simple as the recipe L</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
L<Moose::Cookbook::Extending::Debugging_BaseClassRole>, which shows how to
make a module like C<Moose.pm> itself, with sugar like C<has_table()>.

=head2 Using this Metaclass Trait in Practice

Accessing this new C<table> attribute is quite simple. Given a class
named C<MyApp::User>, we could simply write the following:

my $table = MyApp::User->meta->table;

As long as C<MyApp::User> has arranged to apply the
C<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 C<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 C<table> method from a I<different> trait. In practice, you are unlikely
to encounter this sort of problem.

=head1 RECIPE CAVEAT

This recipe doesn't work when you paste it all into a single file. This is
because the C<< use Moose -traits => 'HasTable'; >> line ends up being
executed before the C<table> attribute is defined.

When the two packages are separate files, this just works.

=head1 SEE ALSO

L<Moose::Cookbook::Meta::Labeled_AttributeTrait> - Labels implemented via
attribute traits
=pod

=for testing can_ok( MyApp::User->meta, 'table' );
is( MyApp::User->meta->table, 'User', 'My::User table is User' );

=head1 AUTHORS

=over 4

=item *

Stevan Little <stevan@cpan.org>

=item *

Dave Rolsky <autarch@urth.org>

=item *

Jesse Luehrs <doy@cpan.org>

=item *

Shawn M Moore <sartak@cpan.org>

=item *

יובל קוג'מן (Yuval Kogman) <nothingmuch@woobling.org>

=item *

Karen Etheridge <ether@cpan.org>

=item *

Florian Ragwitz <rafl@debian.org>

=item *

Hans Dieter Pearcey <hdp@cpan.org>

=item *

Chris Prather <chris@prather.org>

=item *

Matt S Trout <mstrout@cpan.org>

=back

=head1 COPYRIGHT AND LICENSE

This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.

=cut

${this.title}

Code Editor : Table_MetaclassTrait.pod