如何在整个 Rails 活动记录关联链中取消特定模型的默认范围？

Posted 2023-02-15

【中文标题】如何在整个 Rails 活动记录关联链中取消特定模型的默认范围？

【英文标题】：How to unscope the default scope for the specific model in the whole rails active record association chain?

【发布时间】：2017-08-26 00:23:18

【问题描述】：

我正在尝试解决以下问题。我有三个模型：User has_many Camera has_many Recordings。

class AddTables < ActiveRecord::Migration
  def change
    create_table :users
    create_table :cameras do |t|
      t.references :user, null: false, foreign_key: true
      t.timestamp :archived_at, index: true
    end
    create_table :recordings do |t|
      t.references :camera, null: false, foreign_key: true
      t.timestamp :archived_at, index: true
    end
  end
end

相机和记录具有特殊字段“archived_at”以将记录标记为已删除（软删除）。我希望 User#recordings 浏览所有摄像机（任何 Camera.ar​​chived_at），但同时，我希望它只浏览非归档记录（Recording.archived_at == nil）。我尝试了几个案例，但都没有成功。

=== 案例 1 ===

class User < ActiveRecord::Base
  has_many :cameras, ->  unscope where: :archived_at 
  has_many :recordings, through: :cameras
end

class Camera < ActiveRecord::Base
  default_scope  where(archived_at: nil) 

  belongs_to :user
  has_many :recordings
end

class Recording < ActiveRecord::Base
  default_scope  where(archived_at: nil) 

  belongs_to :camera
end

irb(main):013:0> 重新加载！； User.first.recordings(true) 正在重新加载... 用户负载 (0.1ms) SELECT "users".* FROM "users" ORDER BY "users"."id" ASC LIMIT 1 记录负载（0.2ms）选择“记录”。* FROM“记录”INNER JOIN“相机”在“记录”中。“camera_id”=“相机”。“id”在哪里“相机”。“user_id”=$ 1 [[”用户 ID", 1]] => #]>

=== 案例 2 ===

class User < ActiveRecord::Base
  has_many :cameras, ->  unscope where: :archived_at 
  has_many :recordings, through: :cameras
end

class Camera < ActiveRecord::Base
  default_scope  where(cameras: archived_at: nil) 

  belongs_to :user
  has_many :recordings
end

class Recording < ActiveRecord::Base
  default_scope  where(recordings: archived_at: nil) 

  belongs_to :camera
end

irb(main):013:0> 重新加载！； User.first.recordings(true) 正在重新加载... 用户负载 (0.1ms) SELECT "users".* FROM "users" ORDER BY "users"."id" ASC LIMIT 1 记录负载（0.2ms）选择“记录”。* FROM“记录”INNER JOIN“相机”在“记录”中。“camera_id”=“相机”。“id”在哪里“相机”。“user_id”=$ 1 [[”用户 ID", 1]] => #]> irb(main):014:0> 重新加载！； User.first.recordings(true) 正在重新加载... 用户负载 (0.1ms) SELECT "users".* FROM "users" ORDER BY "users"."id" ASC LIMIT 1 记录负载（0.2 毫秒）选择“记录”。*从“记录”INNER JOIN“相机”打开“记录”。“camera_id”=“相机”。“id”其中“记录”。“归档_at”为空且“相机” "."archived_at" 为 NULL AND "cameras"."user_id" = $1 [["user_id", 1]] => #]>

=== 案例 3 ===

class User < ActiveRecord::Base
  has_many :cameras, ->  unscope where: cameras: :archived_at 
  has_many :recordings, through: :cameras
end

class Camera < ActiveRecord::Base
  default_scope  where(cameras: archived_at: nil) 

  belongs_to :user
  has_many :recordings
end

class Recording < ActiveRecord::Base
  default_scope  where(recordings: archived_at: nil) 

  belongs_to :camera
end

irb(main):016:0> 重新加载！； User.first.recordings(true) 正在重新加载... 用户负载 (0.2ms) SELECT "users".* FROM "users" ORDER BY "users"."id" ASC LIMIT 1 记录负载（0.2 毫秒）选择“记录”。*从“记录”INNER JOIN“相机”打开“记录”。“camera_id”=“相机”。“id”其中“记录”。“归档_at”为空且“相机” "."archived_at" 为 NULL AND "cameras"."user_id" = $1 [["user_id", 1]] => #]>

【参考方案1】：

试试这个：

user.rb:

class User < ApplicationRecord
    has_many :cameras
    has_many :recordings, ->  unscope(where: :archived_at).where(recordings: archived_at: nil) , through: :cameras
end

camera.rb:

class Camera < ApplicationRecord
    default_scope  where(archived_at: nil) 
    belongs_to :user
    has_many :recordings
end

recording.rb:

class Recording < ApplicationRecord
    belongs_to :camera
    default_scope  where(archived_at: nil) 
end

这是输出查询：

irb(main):088:0> User.first.recordings
User Load (0.2ms)  SELECT  "users".* FROM "users" ORDER BY "users"."id" ASC LIMIT ?  [["LIMIT", 1]]
Recording Load (0.1ms)  SELECT "recordings".* FROM "recordings" INNER JOIN "cameras" ON "recordings"."camera_id" = "cameras"."id" WHERE "cameras"."user_id" = ? AND "recordings"."archived_at" IS NULL  [["user_id", 1]]

【讨论】：

但缺点是我们必须为每个使用 Recording 的关联添加这样的范围

是的，没错。但是为了缓解这个缺点，您可以创建包含记录关联的关注点，并将其包含在每个模型中。