使用嵌套资源的控制器中的设置值

问题描述：

Product 
- cost 
- id 

Order 
- cost 
- product_id

每次有人下订单，它通过在“新秩序”形式的单选按钮值捕捉PRODUCT_ID。

在控制器创建新订单时，需要将order.cost设置为order.product.cost。按道理我认为代码应该是这样的：

def create 
... 
    @order.cost == @order.product.cost 
... 
end

但是我似乎无法使它在所有的工作，因此我问这个问题在这里。

任何帮助回答（或命名）的问题将不胜感激。

答

语法错误

@order.cost == @order.product.cost #it will compare the product cost & order cost & return boolean value true ot false

它应该是

@order.cost = @order.product.cost

假设你写协会正确模型应该是如下

product.rb

has_many :orders

或der.rb

belongs_to :product

答

另一个选择是指定的订单模型before_create，但如果每一个订单需要以这种方式来创建这个只会工作。

class Order < ActiveRecord::Base 
    has_many :products 
    #this could be has_one if you really want only one product per order 
    accepts_nested_attributes_for :products 
    #so that you can do Order.new(params[:order]) 
    #where params[:order] => [{:attributes_for_product => {:id => ...}}] 
    #which is handled by fields_for in the view layer. 

    #has_one would make this :product 

    before_create :calculate_order_cost_from_product 
    #only run on the first #save call or on #create 

    def calculate_order_cost_from_product 
     self.cost = self.products.first.cost 
     #this could also be self.products.sum(&:cost) 
     #if you wanted the total cost of all the products 

     #has_one would be as you had it before: 
     #self.cost = self.product.cost 
    end 

end

使用嵌套资源的控制器中的设置值

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