Rails 4：無法顯示個別訂單

Question

試圖在我的雜貨應用程序上顯示個別項目。

使用item.product.title & item.quantity。

因爲我想做訂單的小計。目前，我得到

NoMethodError in Orders#show - undefined method `product' for #<OrderItem:0x007fe53514d6e8> 

orders.show.html

<h1>Your Order</h1> 

<table class="table table-striped"> 
    <tr> 
     <th>Customer</th> 
     <td><%= @order.user_id %></td> 
    </tr> 

    <tr> 
     <th>Status:</th> 
     <td><%= @order.status %></td> 
    </tr> 

    <tr> 
     <th>Items:</th> 
     <td><%= @order.order_items.count %></td> 
    </tr> 
    <tr> 
     <th>Items</th> 
     <th>Title</th> 
     <th>Quantity</th> 
     <th>Unit Price</th> 
     <th>Subtotal</th> 
    </tr> 

    <% @order.order_items.each do |item| %> 
    <tr> 
     <td></td> 
     <td><%= item.product.title %></td> <-----Error 
     <td><%= item.quantity %></td> 
     <td><%= item.product.price %></td> 
     <td><%= print_price item.subtotal %></td> 
    <% end %> 

</table> 


<%= link_to 'Edit', edit_order_path(@order) %> | 
<%= link_to 'Back', orders_path %> 

product.rb

class Product < ActiveRecord::Base 
    validates_numericality_of :price 
    validates :stock ,numericality: { greater_than_or_equal_to: 0 } 

    has_many :order_items 
end 

order.item

class OrderItem < ActiveRecord::Base 
    belongs_to :Order 
    belongs_to :Product 

    validates :order_id, :product_id, presence: true 
end 

完全錯誤

NameError in Orders#show 
undefined local variable or method `product' for #<#<Class:0x007fe539003568>:0x007fe5391abd48> 
app/views/orders/show.html.erb:30:in `block in _app_views_orders_show_html_erb__2160818799905733439_70311241143160' 
app/views/orders/show.html.erb:27:in `_app_views_orders_show_html_erb__2160818799905733439_70311241143160' 

Answer 1

訂單項目必須想起來

class OrderItem < ActiveRecord::Base 
    belongs_to :order 
    belongs_to :product 

    validates :order_id, :product_id, presence: true 
end 

最簡單的方法是belongs_to的定義是返回與連接相關聯的對象的方法。所以：產品 - 創建order_item.product。不是：產品