Notes on changing a Many-to-Many to a Self-Referential Many-to-Many

gistfile1.txt

Currently I have Kits and Items. A Kit can contain many Items; an Item can be associated to many Kits.
I also have a join model, KitItem, that allows me to define how many of an Item is associated to a Kit.

Here are the model definitions:

class Kit < ActiveRecord::Base
  belongs_to :category
  has_many   :kit_items, :dependent => :destroy
  has_many   :items, :through => :kit_items
end

class Item < ActiveRecord::Base
  belongs_to :category
  has_many   :kit_items, :dependent => :destroy
  has_many   :kits, :through => :kit_items
end

class KitItem < ActiveRecord::Base
  belongs_to :item
  belongs_to :kit
end

# == Schema Information
#
# Table name: kit_items
#
#  id         :integer(4)      not null, primary key
#  quantity   :integer(4)
#  kit_id     :integer(4)
#  item_id    :integer(4)
#  created_at :datetime
#  updated_at :datetime
#
# Indexes
#
#  index_kit_items_on_item_id  (item_id)
#  index_kit_items_on_kit_id   (kit_id)
#

However, I need to support the concept of a Kit containing other Kits.

I'm not sure how to implement this. The examples I've seen so far are for single table self-joins; 
I've only confused myself when attempting to alter them for my purposes.

Check out this one for a slight improvement:

https://gist.github.com/1912350

After read Jim's comment, I realized my solutions might have missed part of what you need. I have the 'many kits' part, but thought you wanted them in a separate collection. Are you saying you want something like my_kit.contents, and contents will return a heterogenous collection containing kits and items?

I believe I do.

Without regard to implementation, I need the following 'behavior'

kit = Kit.new(:name => "Surf Rider Kit")
kit.kitables.build(:kitable => Item.find_by_name("Twin Set"), :quantity => 1)
kit.kitables.build(:kitable => Kit.find_by_name("Towel Set"), :quantity => 1)
kit.save
kit.items #=> [Twin Set]
kit.kits #=> [Towel Set]
kit.kits.first.items #=> [Bath Towel, Hand Towel, Wash Cloth]
kit.kits.first.kits #=> []
kit.kitables.size #=> 2

Ok, your use is more of a tree, where the edges have a quantity and the nodes are either a kit or an item (another node or a leaf). I read too much of a previous problem into it and have you peer stuff. You could do this by either using STI and having Kit and Item share a table, or have the KitItem be polymorphic as Jim suggested (but that might mean not being able tO traverse back and answer 'what kits is this towel package in?'

More code to follow

Mel, sorry to have spun you off in the wrong direction - I had read too much of a previous problem into your situation and thought you were looking for 'peer' kits, as if you were doing suggestions ("Here are Kits like the one you're looking at!"). Jim's comment points you in the right direction, but you can't do a has_many :through a polymorphic relationship. I think this example gives you what you need though:

https://gist.github.com/1915372

I'm definitely studying this less for the code and more for the magical incantation to summon @bokmann