如何在 ActiveRecord 中执行这样的连接表？答案

【问题标题】：How to perform such join tables in ActiveRecord?如何在 ActiveRecord 中执行这样的连接表？
【发布时间】：2014-04-21 18:03:55
【问题描述】：

我在使用 ActiveRecord 关系模型进行以下连接时需要帮助：

select "access_urls"."id", "controller_urls"."controller", "action_urls"."action" from
"access_urls"
inner join "controller_urls"
on "controller_urls"."id" = "access_urls"."controller_url_id"
inner join "action_urls"
on "action_urls"."id" = "access_urls"."action_url_id"

我有 AccessUrl、ActionUrl 和 ControllerUrl 模型的地方

class AccessUrl < ActiveRecord::Base
  belongs_to :controller_url
  belongs_to :action_url
end

class ActionUrl < ActiveRecord::Base
  has_many :access_urls
  validates :action, presence: true, uniqueness: { message: "já encontra-se em uso." }
end

class ControllerUrl < ActiveRecord::Base
  has_many :access_urls
  validates :controller, presence: true, uniqueness: { message: "já encontra-se em uso." }
end

谁能帮帮我？

【问题讨论】：

标签： sql ruby-on-rails rails-activerecord

【解决方案1】：

使用joins：

result = AccessUrl.joins(
  :controller_url, :action_url
).select(
  'access_urls.id, controller_urls.control, action_urls.action'
)

这将为您提供一个关系result，其中包含AccessUrl 的对象。您可以循环访问 result 并访问选定的列：

result.each do |r| 
  # r.id
  # r.control
  # r.action
end

【讨论】：