Why not adopt me?
NAME
Class::DBI::Relationship::HasVariant - columns with varying types
VERSION
version 0.02
$Id: HasVariant.pm,v 1.3 2004/10/12 16:53:07 rjbs Exp $
SYNOPSIS
Using a class to transform values:
package Music::Track::Attribute;
use base qw(Music::DBI);
Music::Track::Attribute->add_relationship_type(
has_variant =>
'Class::DBI::Relationship::HasVariant'
);
Music::Track::Attribute->table("trackattributes");
Music::Track::Attribute->has_variant(
attr_value => 'Music::Track::Attribute::Transformer',
inflate => 'inflate',
deflate => 'deflate'
);
Using subs (this is a wildly contrived example):
Boolean::Stored->has_variant(
boolean => undef,
deflate => sub {
return undef if ($_[0] and $_[0] == 0);
return 1 if $_[0];
return 0;
}
);
DESCRIPTION
The has_a
relationship in Class::DBI works like this:
__PACKAGE__->has_a($columnname => $class, %options);
The column is inflated into an instance of the named class, using methods from the options or default methods. The inflated value must be of class $class
, or an exception is thrown.
The has_variant
relationship allows one column to inflate to different types. If a class is given, it is not used for type checking, but for finding a transformation method.
EXAMPLES
__PACKAGE__->has_variant(
variant => 'Variant::Auto',
inflate => 'inflate',
deflate => 'deflate'
);
This example will pass the value of the "variant" column to Variant::Auto's <inflate
> method before returning it, and to its <deflate
> method before storing it.
__PACKAGE__->has_variant(
variant => undef,
inflate => sub {
return ($_[0] % 2) ? Oddity->new($_[0]) : Normal->new($_[0])
}
deflate => sub { $_[0]->isa('Oddity') ? $_[0]->value : $_[0]->number }
);
The above example will inflate odd numbers to Oddity objects and other values to Normals. Oddities are deflated with the <value
> methods, and others with the <number
> method.
WARNINGS
My understanding of the Class::DBI internals isn't beyond question, and I expect that I've done something foolish inside here. I've tried to compensate for my naivety with testing, but stupidy may have leaked through. Feedback is welcome.
AUTHOR
Ricardo SIGNES <<rjbs@cpan.org
>>
COPYRIGHT
(C) 2004, Ricardo SIGNES, and released under the same terms as Perl itself.