与has_many建立联系：通过多个模型

请帮助了解如何使用此树执行@project.payments ：

 Project |__Stages |__Costs |__Payments 

project.rb

  has_many :stages has_many :costs, :through => stages 

stage.rb

 belongs_to :project has_many :costs has_many :payments :through => costs 

cost.rb

 belongs_to :stage has_many :payments 

payment.rb

 belongs_to :cost 

Answer 1

注意：由于这是一个嵌套的has_many：through关系，它只适用于Rails 3.1+（3.1的RC4出来）

project.rb

 has_many :payments, :through => costs