DataMapper: Hierarchy System

[DtY]

What I am trying to achieve is a hierarchy of categories. What it needs to do is have categories, each with an optional parent, and optional children. Then, have an easy way to get all the categories that don't have a parent (top level categories), as well as get all the children of a category (which wouldn't be trouble at all).

What I was thinking was making a special category called top level or something, which would be it's own parent (like the object class in Ruby), and then everything in there would be a subcategory of that. Is that the best method?

So something like this:

Ruby:

class Category     include DataMapper::Resource     property :id,   Serial     property :name, String         has 1, :parent #Not sure on how to make is have a Category, but not accessed through .category     has n, :children #Same thing here end

[DtY]

Okay, I got it figured out. Apparently one to many relationships can be empty, so top level categories have the parent nil.

Ruby:

require 'rubygems' require 'dm-core' require 'dm-validations' require 'dm-timestamps' require 'dm-types' DataMapper.setup(:default, "sqlite3://#{Dir.pwd}/db.sqlite3") class Category     include DataMapper::Resource     property :id,   Serial     property :name, String         #Hierarchy     belongs_to :parent, :class_name=>'Category', :child_key=>[:parent_key]     has n, :children, :class_name=>'Category' end def Category.topLevels     all :parent_key=>nil end DataMapper.auto_upgrade!

[gianni]

Isn't DataMapper awesome?

[DtY]

So much!