Question

I’m having a problem with an :has_many => :through association which references another :has_many => :through association.

I have a User->Cart->CartItem->Product model setup going in my rails application. Here are the model associations:

class User < ActiveRecord::Base
  has_many :purchases,  :class_name => "Cart",
                        :dependent => :destroy,
                        :conditions => {:purchased => true}
  has_many :items,      :through => :purchases,
                        :readonly => true
  has_many :products,   :through => :purchases,
                        :readonly => true
end

class Cart < Activerecord::Base
  belongs_to :user
  has_many :items,    :class_name => "CartItem",
                      :dependent => :delete_all                 
  has_many :products, :through => :items
end

class CartItem < ActiveRecord::Base
  belongs_to :cart
  belongs_to :product
end

The idea is that a cart has many cart_items, which are just references to existing products. After a cart is marked as purchase, a user should have access to products directly via user.products.

Anyway… I can not figure out how to setup my User model so that the relationship is possible. I keep getting the following error:

Invalid source reflection macro :has_many :through for has_many :products,
:through => :purchases. Use :source to specify the source reflection.

I’m assumming it wants me to add a :source attribute to the has_many :products assoc. in the User model, but that seems silly considering the source association is named identically (and it doesn’t work when I add :source => :products anyway).

Does anyone know how I could get this to work? I’d really appreciate any suggestions!

Sorry if this question has been asked before, but I’ve been searching and I can’t find an answer. Thanks in advance.

Answer 1

Rails won’t allow you chain nested has_many :through associations like that.

There’s a similar question here: Ruby-on-Rails: Multiple has_many :through possible?