通过另一个外键关联外键

Question

I've these 3 Models

class User < ActiveRecord::Base
  has_many :answers, :as => :owner
end

class Answer < ActiveRecord::Base
  belongs_to :owner, :polymorphic => true
  has_one :test  
end

class Test < ActiveRecord::Base
  belongs_to :answer
end

so I want to associate the Test model with User model through Answer Model without need of creating new association between them, so I put the following into Test Model:

has_one :owner, :through => :answer

but it doesn't work and I got this error

ActiveRecord::HasManyThroughAssociationPolymorphicSourceError: Cannot have a has_many :through association 'Test#owner' on the polymorphic object 'Owner#owner'.

any help?

Answer 1

在Test ：

delegate :owner, :to => :answer

Answer 2

You have to specify source_type option as owner is a polymorphic association

class Test < ActiveRecord::Base
  belongs_to :answer
  has_one :owner, :through => :answer, :source_type => "User"
end