ruby-on-rails - 使用关系数据库

Question

我有三个表 Business、Users 和 Subscriptions。目标是能够获得与用户关联的企业名称。结果应该是用户在订阅中注册的一组企业名称

表格列表

Schema |       Name        | Type  |
--------+-------------------+-------
 public | businesses        | table 
 public | subscriptions     | table 
 public | users             | table

---

业务表

  Column   |            Type                                                        
------------+-----------------------------
 id         | integer                      
 name       | character varying(255)       
 created_at | timestamp without time zone  
 updated_at | timestamp without time zone  

商业模式

class Business < ActiveRecord::Base

end

---

订阅表

   Column    |            Type                                   
-------------+-----------------------------
 id          | integer                     
 user_id     | integer                      
 business_id | integer                      
 created_at  | timestamp without time zone  
 updated_at  | timestamp without time zone

订阅模式

class Subscription < ActiveRecord::Base
   belongs_to :user
   belongs_to :business
end

---

用户表

     Column      |            Type                                   
-----------------+-----------------------------
 id              | integer                 
 username        | character varying(255)       
 password_digest | character varying(255)       
 email           | character varying(255)       
 created_at      | timestamp without time zone  
 updated_at      | timestamp without time zone 

用户模型

 class User < ActiveRecord::Base
       has_secure_password
       has_many :subscriptions
    end

---

Rails 控制台

 u = User.find(1)
 u.subscriptions.businesses.name

 Response: undefined method `business'

Answer 1

您可以使用 Rails 的内置 includes 仅通过一个查询来完成此操作，而不是对每个订阅进行额外的查询(如 Alireza 的回答)。方法:

subscriptions = u.subscriptions.includes(:business)

这将返回所有订阅的关系，包括它们的关联业务。现在您无需执行额外查询即可获取公司名称:

business_names = subscriptions.map {|sub| sub.business.name }

我认为您也可以使用 pluck 一步完成此操作:

business_names = u.subscriptions.includes(:business).pluck("businesses.name")

我不确定 pluck 是否与 includes 配合得很好，但值得一试。