nested has_many :through in rails 3

Question

I know Rails doesn't support nested has_many :through relationships, though there's been talk and an open ticket about a patch since as early as Rails 2.

I did come across a plugin that's pretty slick, but the master branches don't work with Rails 3 and I'm hesitant to use it for mission critical tasks in the app hence the lack of active recent development. So -- what's the best way to deal with these relations.

class Author < ActiveRecord::Base
  has_many :contracts
  has_many :products, :through => :contracts

class Product < ActiveRecord::Base
  has_many :contracts
  has_many :orders
  has_many :authors, :through => :contracts

class Contracts < ActiveRecord::Base
  belongs_to :author
  belongs_to :product

So, all the being what it is it would be great to be able to get at orders this by adding this to the Author model:

has_many :orders, :through => :products

But alas, you cannot -- at least without the plugin. So, my question is what's the best approach to accessing all of an author's orders when the only association is between the join model, Contracts?

Answer 1

If you're not trying to create objects through the nested association, and you want to use it for lookup only, then scopes in Rails 3 are a great way to do this. Alternatively you could implement a class method.

I've had this kind of thing as an example in a class I taught recently, the Rails 3 version of the code is here: https://github.com/wolframarnold/Efficient-TDD-Rails3/blob/master/app/models/user.rb

See the definition of the items method. The specs are here: https://github.com/wolframarnold/Efficient-TDD-Rails3/blob/master/spec/models/user_orders_spec.rb

Rails 3.1 update: As one commenter already noted, Rails 3.1 does support has_many :through associations more than one level deep.