Ruby On Rails活动记录中的belongs_to关联4

Question

我有问题。我需要知道是否存在某种方式使用以下关联以更简单的方式从一个类导航到另一个类

SCHEMA

ActiveRecord::Schema.define(version: 20140712054858) do

  create_table "customers", force: true do |t|
    t.string   "name"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  create_table "orders", force: true do |t|
    t.integer  "customer_id"
    t.datetime "order_date"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

end

customer.rb

class Customer < ActiveRecord::Base
end

order.rb

class Order < ActiveRecord::Base
     belongs_to :customer
   end

我的使用方法

  2.0.0-p481 :044 > @customer1=Customer.create(:name=>"John")
   (0.2ms)  begin transaction
  SQL (0.6ms)  INSERT INTO "customers" ("created_at", "name", "updated_at") VALUES (?, ?, ?)  [["created_at", Sat, 12 Jul 2014 06:18:24 UTC +00:00], ["name", "John"], ["updated_at", Sat, 12 Jul 2014 06:18:24 UTC +00:00]]
   (162.3ms)  commit transaction
 => #<Customer id: 4, name: "John", created_at: "2014-07-12 06:18:24", updated_at: "2014-07-12 06:18:24"> 
2.0.0-p481 :045 > @order1=Order.new
 => #<Order id: nil, customer_id: nil, order_date: nil, created_at: nil, updated_at: nil> 
2.0.0-p481 :046 > @order1.order_date=Time.now
 => 2014-07-12 03:19:31 -0300 
2.0.0-p481 :047 > @order1.customer_id=@customer.id
 => 1 
2.0.0-p481 :048 > @order1.save
   (0.2ms)  begin transaction
  SQL (0.7ms)  INSERT INTO "orders" ("created_at", "customer_id", "order_date", "updated_at") VALUES (?, ?, ?, ?)  [["created_at", Sat, 12 Jul 2014 06:20:03 UTC +00:00], ["customer_id", 1], ["order_date", Sat, 12 Jul 2014 06:19:31 UTC +00:00], ["updated_at", Sat, 12 Jul 2014 06:20:03 UTC +00:00]]
   (171.1ms)  commit transaction
 => true 

没有某种方式让@ customer1。@ order1和？自动映射？

Answer 1

您可以像Customer这样设置反向关联：

class Customer < ActiveRecord::Base
  has_many :orders
end

这样您就可以更轻松地创建Order记录：

@order1 = @customer1.orders.create(order_date: Time.now)

通过在has_many :orders中说Customer，Rails假定Order表格中有customer_id，在您的情况下，它是开箱即用的。

Answer 2

<强>协会

您当然需要查看ActiveRecord Associations - belongs_to需要与has_many匹配：

所以你的模型看起来像：

#app/models/customer.rb
Class Customer < ActiveRecord::Base
    has_many :orders
end

#app/models/order.rb
Class Order < ActiveRecord::Base
    belongs_to :customer
end

这一点非常重要 - 当您创建模型的实例时，您基本上实例化了一个Ruby对象。您的对象的attributes将从表格的列中提取，更重要的是，您可以使用associations

整合更多对象/关联数据

使用has_many或belongs_to创建一种方法，将对象附加到当前/父级对象 - 这意味着您可以调用以下内容：

#app/controllers/customers_controller.rb
Class CustomersController < ApplicationController
   def show
      @customer = Customer.find params[:id]
      @orders = @customer.orders
   end
end