Rails - specifying has_many for a parent in polymorphic association

Question

I currently have some models: User, Dealer, Sale and Role. Role has a polymorphic belongs_to relationship with Dealer and Sale, and belongs_to User (see code below).

My query is this: how can I specify a has_many :dealers, :through => :roles relationship on User for Dealer and Sale? The role model that the User model would be associating through belongs_to either a Dealer or a Sale, and as such the relationship in this format does not work.

class User < ActiveRecord::Base
  has_many :roles
  has_many :sales, :through => :roles
  has_many :appraisals, :through => :roles
  has_many :dealers, :through => :roles
end

class Dealer < ActiveRecord::Base
  has_many :roles, :as => :role_originator
  has_many :users, :through => :roles
end

class Sale < ActiveRecord::Base
  has_many :roles, :as => :role_originator
  has_many :users, :through => :roles
end

class Role < ActiveRecord::Base
  belongs_to :role_type
  belongs_to :user
  belongs_to :role_originator, :polymorphic => true
end

Would appreciate any assistance here.

Answer 1

发现：source选项后，我能够解决此问题-参见http://guides.rubyonrails.org/association_basics.html#has_many-association-reference （第4.3.2.20部分）。