选定值的 ActiveRecord 查询

编程问答 2022-05-02

问题描述

我有这个聊天服务的模型设计：


class ChatRoom < ApplicationRecord
  has_many :chat_room_infos,dependent: :destroy

  has_many :employees,through: :chat_room_infos,source: :chattable,source_type: Employee.name,dependent: :destroy
  has_many :employers,source_type: Employer.name,dependent: :destroy
end

class ChatRoomInfo < ApplicationRecrod
  belongs_to :chat_room
  belongs_to :chattable,polymorphic: true

  has_many :employees,through: :chat_room # Employees in the same chat room
  has_many :employers,through: :chat_room # Employers in the same chat room
end

我想通过参与者数组（包含任意数量的ChatRoom和Employee）找到Employer

为了做到这一点，我首先要找到参与者的ChatRoomInfo：

chat_room.rb

scope :where_participants_in,->(users) { joins(:chat_room_infos).merge(ChatRoomInfo.where(chattable: users)) }

产生以下查询：

> ChatRoom.where_participants_in([Employee.find(8),Employer.find(3)])
 
SELECT
    `chat_rooms`.* 
FROM
    `chat_rooms`
    INNER JOIN `chat_room_infos` ON `chat_room_infos`.`chat_room_id` = `chat_rooms`.`id` 
WHERE
    ( `chat_room_infos`.`chattable_type` = 'Employee' AND `chat_room_infos`.`chattable_id` = 8 
    OR `chat_room_infos`.`chattable_type` = 'Employer' AND `chat_room_infos`.`chattable_id` = 3 )

然后，我想通过匹配的计数来查询 ChatRoom。在这种情况下，如果匹配的计数正好是 2，那么它就是我想要的 ChatRoom：

chat_room.rb

scope :where_participants_count,->(users) { where_participants_in(users).count }

> ChatRoom.where_participants_count([Employee.find(8),Employer.find(3)])

SELECT
    COUNT(*) 
FROM
    `chat_rooms`
    INNER JOIN `chat_room_infos` ON `chat_room_infos`.`chat_room_id` = `chat_rooms`.`id` 
WHERE
    (
        `chat_room_infos`.`chattable_type` = 'Employee' 
        AND `chat_room_infos`.`chattable_id` = 8 
    OR `chat_room_infos`.`chattable_type` = 'Employer' 
    AND `chat_room_infos`.`chattable_id` = 3)

=> 2 # the first result is two

所以我需要做的就是通过这个 select sql 查询 ChatRoom。

我尝试过这样的事情：

chat_room.rb

scope :where_participants,->(users) { where(where_participants_count(users).eq(users.count)) }

但我收到此错误：

NoMethodError（2:Integer 的未定义方法 `eq'）

我该如何解决这个问题？这是我想使用 activerecord 方法获取的示例查询：

SELECT * FROM `chat_rooms` WHERE (SELECT
  COUNT(`chat_rooms`.`id`) AS count 
FROM
  `chat_rooms`
  JOIN `chat_room_infos` ON `chat_room_infos`.`chat_room_id` = `chat_rooms`.`id` 
WHERE
  (`chat_room_infos`.`chattable_type` = 'Employer' AND `chat_room_infos`.`chattable_id` = 3) OR
  (`chat_room_infos`.`chattable_type` = 'Employee' AND `chat_room_infos`.`chattable_id` = 8)) = 2

解决方法

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polymorphic-associationsruby-on-rails