小编Ter*_*hen的帖子

模型是这样的:

class Contract < ActiveRecord::Base  
  belongs_to :buyer, :class_name => 'Customer', :foreign_key => 'buyer_customer_id' 
  belongs_to :user, :class_name => 'Customer', :foreign_key => 'user_customer_id'
  belongs_to :currency
end  

class Customer < ActiveRecord::Base  
  has_many :as_buyer_in_contracts, :class_name => 'Contract', :foreign_key => 'buyer_customer_id'  
  has_many :as_user_in_contracts, :class_name => 'Contract',:foreign_key => 'user_customer_id'  
end

class Currency < ActiveRecord::Base
  has_many :contracts
end

以下是数据:

Contract
+----+-------------------+------------------+-------------+
| id | buyer_customer_id | user_customer_id | currency_id |
+----+-------------------+------------------+-------------+
|  1 |         1         |        3         |      3      |
|  2 |         2         |        2         | …