如何在Ruby on Rails/ActiveRecord中克隆模型？

Question

我試圖創建一個郵件的多個副本的用戶：

users.each do |user| 
    new_message = message.clone 
    new_message.to = user 
    new_message.save! 
end 

然而，這並不一日後用戶的工作。下面是錯誤消息的一部分：

SQL (0.7ms) INSERT INTO "messages" ("content", "to_id") VALUES (?, ?) [["content", "abc"], ["to_id", 1]] 
    (2.5ms) commit transaction 
    User Load (0.1ms) SELECT "users".* FROM "users" WHERE "users"."id" = 2 LIMIT 1 
    (0.0ms) begin transaction 
    SQL (0.5ms) INSERT INTO "messages" ("content", "id", "to_id") VALUES (?, ?, ?) [["content", "abc"], ["id", 6], ["to_id", 2]] 
SQLite3::ConstraintException: PRIMARY KEY must be unique: INSERT INTO "messages" ("content", "id", "to_id") VALUES (?, ?, ?) 
    (0.0ms) rollback transaction 
Completed 500 Internal Server Error in 130.1ms 

ActiveRecord::StatementInvalid (SQLite3::ConstraintException: PRIMARY KEY must be unique: INSERT INTO "messages" ("content", "id", "to_id") VALUES (?, ?, ?)): 

正如你所看到的，問題是循環運行的第二次，message.clone必須包含以前new_message的id。

克隆許多用戶的郵件記錄的正確方法是什麼？當然，我可以手動將每個屬性（我有一個批次多於content和to_id）複製到一個新的新對象Message。但我想知道是否有更好的方法。

Answer 1

您可以使用dup，與該id，created_at和updated_at設置爲nil。這將確保不會拋出主鍵異常，但是如果有其他唯一驗證，它們將失敗。你必須分開處理它們。

users.each do |user| 
    new_message = message.dup 
    new_message.to = user 
    new_message.save! 
end