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.IX Title "Moose::Cookbook::Meta::Table_MetaclassTrait 3pm"
.TH Moose::Cookbook::Meta::Table_MetaclassTrait 3pm 2024-01-21 "perl v5.38.2" "User Contributed Perl Documentation"
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.SH NAME
Moose::Cookbook::Meta::Table_MetaclassTrait \- Adding a "table" attribute as a metaclass trait
.SH VERSION
.IX Header "VERSION"
version 2.2207
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 4
\&  # in lib/MyApp/Meta/Class/Trait/HasTable.pm
\&  package MyApp::Meta::Class::Trait::HasTable;
\&  use Moose::Role;
\&  Moose::Util::meta_class_alias(\*(AqHasTable\*(Aq);
\&
\&  has table => (
\&      is  => \*(Aqrw\*(Aq,
\&      isa => \*(AqStr\*(Aq,
\&  );
\&
\&  # in lib/MyApp/User.pm
\&  package MyApp::User;
\&  use Moose \-traits => \*(AqHasTable\*(Aq;
\&
\&  _\|_PACKAGE_\|_\->meta\->table(\*(AqUser\*(Aq);
.Ve
.SH DESCRIPTION
.IX Header "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.
.PP
In this example, the table name is just a string, but in a real ORM
the table might be an object describing the table.
.SH "THE METACLASS TRAIT"
.IX Header "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 \f(CW\*(C`Moose.pm\*(C'\fR itself, with sugar like \f(CWhas_table()\fR.
.SS "Using this Metaclass Trait in Practice"
.IX Subsection "Using this Metaclass Trait in Practice"
Accessing this new \f(CW\*(C`table\*(C'\fR attribute is quite simple. Given a class
named \f(CW\*(C`MyApp::User\*(C'\fR, we could simply write the following:
.PP
.Vb 1
\&  my $table = MyApp::User\->meta\->table;
.Ve
.PP
As long as \f(CW\*(C`MyApp::User\*(C'\fR has arranged to apply the
\&\f(CW\*(C`MyApp::Meta::Class::Trait::HasTable\*(C'\fR 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 \f(CW\*(C`table\*(C'\fR method:
.PP
.Vb 2
\&  $table = MyApp::User\->meta\->table
\&      if MyApp::User\->meta\->can(\*(Aqtable\*(Aq);
.Ve
.PP
In theory, this is not entirely correct, since the metaclass might be getting
its \f(CW\*(C`table\*(C'\fR method from a \fIdifferent\fR trait. In practice, you are unlikely
to encounter this sort of problem.
.SH "RECIPE CAVEAT"
.IX Header "RECIPE CAVEAT"
This recipe doesn't work when you paste it all into a single file. This is
because the \f(CW\*(C`use Moose \-traits => \*(AqHasTable\*(Aq;\*(C'\fR line ends up being
executed before the \f(CW\*(C`table\*(C'\fR attribute is defined.
.PP
When the two packages are separate files, this just works.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Moose::Cookbook::Meta::Labeled_AttributeTrait \- Labels implemented via
attribute traits
=pod
.SH AUTHORS
.IX Header "AUTHORS"
.IP \(bu 4
Stevan Little <stevan@cpan.org>
.IP \(bu 4
Dave Rolsky <autarch@urth.org>
.IP \(bu 4
Jesse Luehrs <doy@cpan.org>
.IP \(bu 4
Shawn M Moore <sartak@cpan.org>
.IP \(bu 4
יובל קוג'מן (Yuval Kogman) <nothingmuch@woobling.org>
.IP \(bu 4
Karen Etheridge <ether@cpan.org>
.IP \(bu 4
Florian Ragwitz <rafl@debian.org>
.IP \(bu 4
Hans Dieter Pearcey <hdp@cpan.org>
.IP \(bu 4
Chris Prather <chris@prather.org>
.IP \(bu 4
Matt S Trout <mstrout@cpan.org>
.SH "COPYRIGHT AND LICENSE"
.IX Header "COPYRIGHT AND LICENSE"
This software is copyright (c) 2006 by Infinity Interactive, Inc.
.PP
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.