--- /dev/null
+class ProductTariff < ActiveRecord::Base\r
+ set_primary_keys :product_id, :tariff_id, :tariff_start_date\r
+ belongs_to :product, :foreign_key => :product_id\r
+ belongs_to :tariff, :foreign_key => [:tariff_id, :tariff_start_date]\r
+end\r