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.IX Title "Moose::Cookbook::Meta::Table_MetaclassTrait 3"
.TH Moose::Cookbook::Meta::Table_MetaclassTrait 3 "2021-11-07" "perl v5.26.3" "User Contributed Perl Documentation"
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.if n .ad l
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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 2.2201
.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 \*(L"table\*(R"
attribute. This trait is for classes associated with a \s-1DBMS\s0 table, as one
might do for an \s-1ORM.\s0
.PP
In this example, the table name is just a string, but in a real \s-1ORM\s0
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 \*(L"\s-1SYNOPSIS\*(R"\s0 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(CW\*(C`has_table()\*(C'\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.