Rails的N + 1引用相同的模型時兩次

Question

我有2種型號：

class User < ActiveRecord::Base 

end 

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

，我想所有的用戶收到的消息，以便在messages_controller.rb我有：

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

    respond_with messages 
    end 

這項服務的工作，但在日誌中我可以看到經典的N + 1個問題：

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，我想通過增加，以解決它：

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

    respond_with messages 
    end 

但後來我得到以下錯誤：

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') 

如何可以解決嗎？ 我想返回一組消息 - 不是用戶和用戶內部設置的消息。但沒有N + 1問題

EDIT

2個模型之間的連接是通過郵件表完成的，這裏是遷移（字段發件人，收件人），所以我不需要的users.message_id在users 。此外，任何用戶都可以發送/接收多條消息，也許我的實現不反映？應該怎麼做？

這裏是消息遷移：

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

嘗試

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