Question

某些字段表City

create_table "cities", force: :cascade do |t|
t.string "name"

某些字段表顺序

create_table "orders", force: :cascade do |t|
t.integer "count"
t.integer "first_city_id"
t.integer "last_city_id"

模型订单

class Order < ActiveRecord::Base
belongs_to :city, inverse_of: :city
end

模型城市

class City < ActiveRecord::Base
has_many :orders, inverse_of: :order
end

来自Order in view

的工作输出数据

<% @order.each do |orders| %>
<p> <%= orders.count %> </p>
<% end %>

控制器中的方法

def edit
@orders= Order.all
@order=Order.where(:user_id == current_user)
end

如果Order表中的first_city_id或last_city_id包含City Table的id必需条目，如何从名称Sity表中获取值？

Answer 1

您应按如下方式设置订单关联：

class Order < ActiveRecord::Base
  belongs_to :first_city, class_name: "City" # it would use first_city_id as the foreign key by default to access city table
  belongs_to :last_city, class_name: "City"
end

从订单中获取第一个/最后一个城市名称变得简单：

@order = Order.first

@order.first_city.name
@order.last_city.name

如果您想从订单列表中获取第一个/最后一个城市名称，则应使用includes或joins来避免n + 1查询：

@orders = Order.includes(:first_city, :last_city)

<% @orders.each do |order| %>
  <p> First City: <%= order.first_city.name %> </p>
  <p> Last City: <%= order.last_city.name %> </p>
<% end %>

或

@orders = Order.
  joins("LEFT JOIN cities AS first_cities ON first_cities.id = orders.first_city_id").
  joins("LEFT JOIN cities AS last_cities ON last_cities.id = orders.last_city_id").
  select("orders.*, first_cities.name AS first_city_name, last_cities.name AS last_city_name")

<% @orders.each do |order| %>
  <p> First City: <%= order.first_city_name %> </p>
  <p> Last City: <%= order.last_city_name %> </p>
<% end %>

您可以从这两个文档获得更多信息和帮助＆＃34; RailsGuides - Active Record Associations＆＃34;和＆＃34; RailsGuides - Active Record Query Interface＆＃34;。

从相关表，rails获取数据

1 个答案: