tubbo · January 4, 2017 21:25
diff --git a/order.rb b/order.rb
 class Order < ApplicationRecord
  has_many :order_items, dependent: :destroy
  
  def amount
    order_items.sum :total_price
  end
 end
diff --git a/order_item.rb b/order_item.rb
 class OrderItem < ApplicationRecord
 end
	class Order < ApplicationRecord
	has_many :order_items, dependent: :destroy

	def amount
	order_items.sum :total_price
	end
	end