两次引用同一模型时提供 N+1 导轨

Question

>我有 2 个模型：

class User < ActiveRecord::Base
end
class Message < ActiveRecord::Base
  has_one :sender, :class_name => 'User'
  has_one :recipient, :class_name => 'User'
end

我想获取用户收到的所有消息，因此messages_controller.rb我有：

  def messages_to_user
    messages = Message.where(recipient_id: current_user.id)
    respond_with messages
  end

此服务有效，但在日志中我可以看到经典的N + 1问题：

Started GET "/messages_to_user" for 127.0.0.1 at 2017-01-22 15:35:01 +0200
Processing by MessageController#user as */*
  User Load (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ?  ORDER BY "users"."id" ASC LIMIT 1  [["id", 2]]
  Message Load (0.0ms)  SELECT "messages".* FROM "messages" WHERE "messages"."recipient_id" = ?  [["recipient_id", 2]]
[active_model_serializers]   User Load (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 2]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 2]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 2]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 2]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 2]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 2]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 2]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 2]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 2]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 2]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 2]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 2]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 2]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 2]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 2]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 2]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 2]]
[active_model_serializers]   CACHE (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 2]]
[active_model_serializers] Rendered ActiveModel::Serializer::CollectionSerializer with ActiveModelSerializers::Adapter::Attributes (42.01ms)
Completed 200 OK in 217ms (Views: 63.0ms | ActiveRecord: 3.0ms)

所以我试图通过添加includes来解决它：

  def messages_to_user
    messages = Message.includes(:recipient).where(recipient_id: current_user.id)
    respond_with messages
  end

但是后来我收到以下错误：

SQLite3::SQLException: no such column: users.message_id: SELECT "users".* FROM "users" WHERE "users"."message_id" IN ('1', '2', '3', '4', '5', '6', '7', '8', '9')

如何修复？我想返回一个消息集合 - 不是用户和用户内部设置的消息。但没有 N+1 问题

编辑

2 个模型之间的连接是通过消息表完成的，这里是迁移（字段发件人、收件人），所以我不需要users中的users.message_id. 此外，任何用户都可以发送/接收多条消息，也许我的实现没有反映这一点？ 应该怎么做？

以下是邮件迁移：

class CreateMessages < ActiveRecord::Migration
  def change
    create_table :messasges do |t|
      t.string :title
      t.references :sender, index: true, foreign_key: true
      t.references :recipient, index: true, foreign_key: true
      t.string :content
      t.timestamps null: false
    end
  end
end

Answer 1

尝试

messages = Message.includes(:recipient).references(:recipient).where(recipient_id: current_user.id)