Greetings,
I have a tree of categories that looks like this:
CREATE TABLE `categories` (
`id` int(11) NOT NULL auto_increment,
`name` varchar(255) NOT NULL,
`description` text NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE `category_map` (
`id` int(11) NOT NULL auto_increment,
`child` int(11) NOT NULL,
`parent` int(11) NOT NULL,
PRIMARY KEY (`id`),
FOREIGN KEY (`child`) REFERENCES `categories` (`id`),
FOREIGN KEY (`parent`) REFERENCES `categories` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
I found this structure a lot easier than dealing with a self-joining
table, even though my application has no need for multiple parents
(not yet, anyway.) However, this means that when I call ->children on
a Category object, I get back a list of CategoryMaps instead of other
Categories. So to make this easier I did the following in my
Categories class:
__PACKAGE__->has_many( _parents => 'MyThing::DB::CategoryMap', 'child' );
__PACKAGE__->has_many( _children => 'MyThing::DB::CategoryMap', 'parent' );
sub children {
my $self = shift;
my @kids = $self->_children;
return map { $_->child } @kids;
}
sub parent {
my $self = shift;
my @parents = $self->_parents;
# only allow one parent for now
return $parents[0]->parent;
}
This seems to work just fine. However, I wonder if there are any
gotchas about this structure that I haven't considered, and in
particular, I wonder if there is a standard DBIC-ish way to accomplish
this which I have overlooked.
Mike
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