「C＃中IEntityChangeTracker的多個實例無法引用實體對象」

Question

需要此幫助。 我需要將會話中的一些數據保存到數據庫控制器操作中。但我得到了「一個實體對象不能被C＃中的IEntityChangeTracker的多個實例引用」的錯誤 answer.Add（answer）;

有人可以幫我嗎？

Questionare questionare = unitOfWork.QuestionareRepository.GetByID(id); 



      SADEntitiesContext db = new SADEntitiesContext(); 

      foreach (Question question in questionare.Questions) 
      { 
       //check if there are data in Session and save it 
       _question = "question"+question.QuestionID.ToString(); 


       if (Session[_question] != null) 
       { 

        var answer = new Answers(); 
        if (TryUpdateModel(answer)) 
        { 

        questionanswer = (QuestionAnswerData)Session[_question]; 
        int qID = Int16.Parse(questionanswer.QuestionID); 
        var answertoupdate = answer.GetAnswer(qID, questionanswer.UserID, questionanswer.EmployeID); 


        //db.Answers.Remove(answertoupdate); 


        answer.UserName = questionanswer.UserID; 
        answer.Answer = db.AnswerChoices.Find(Int16.Parse(questionanswer.AnswerID)); 
        answer.AnsweredAt = DateTime.Now; 
        answer.locked = false; 
        answer.Question = question; 
        answer.Questionare = questionare; 
        if (questionanswer.EmployeID != null) 
        { 
         answer.AnswerAboutUser = questionanswer.EmployeID; 
        } 
        if (answertoupdate != null) 
        { 
         answertoupdate = answer; 

         ok = (answertoupdate.Save() > 0); 
        } 

        else 
        { 
         answer.Add(answer); 


         ok = (answer.Save() > 0); 
        } 
        } 
       } 

答案類 公共類答案 {

SADEntitiesContext db = new SADEntitiesContext(); 

    public int AnswersId { get; set; } 

    //[Display(Name = "DataResposta", ResourceType = typeof(Resources))] 
    public DateTime AnsweredAt { get; set; } 

    //[Display(Name = "bloqueado", ResourceType = typeof(Resources))] 
    public bool locked { get; set; } 

    // [Display(Name = "UserName", ResourceType = typeof(Resources))] 
    public string UserName { get; set; } 

    //[Display(Name = "AnswersAboutUser", ResourceType = typeof(Resources))] 
    public string AnswerAboutUser { get; set; } 

    //[Display(Name = "Resposta", ResourceType = typeof(Resources))] 
    public virtual AnswerChoices Answer { get; set; } 

    //[Display(Name = "Questionare", ResourceType = typeof(Resources))] 
    public virtual Questionare Questionare { get; set; } 

    //[Display(Name = "QuestionID", ResourceType = typeof(Resources))] 
    public virtual Question Question { get; set; } 


    // 
    // Persistence 

    public int Save() 
    { 
     return db.SaveChanges(); 
    } 


    public Answers GetAnswer(int questionID, string employeID, string userID) 
    { 
     return db.Answers 
      .Where(e => e.UserName == userID 
              && e.Question.QuestionID == questionID 
              && e.AnswerAboutUser == employeID) 

             .FirstOrDefault(); 

    } 

    public Answers GetAnswer(int id) 
    { 
     return db.Answers.SingleOrDefault(d => d.AnswersId == id); 
    } 

    // 
    // Insert/Delete Methods 

    public void Add(Answers _answer) 
    { 
     db.Answers.Add(_answer); 
     db.SaveChanges(); 
    } 
} 

}

Answer 1

你的問題是你是從一個上下文調用一個答案：

answer.Answer = db.AnswerChoices.Find(Int16.Parse(questionanswer.AnswerID)); 

，然後嘗試在Answer類中使用不同的方法保存它：

SADEntitiesContext db = new SADEntitiesContext(); 

最快的解決辦法，您的問題將能夠設置在你的答案類的背景下，讓你不能輕易的上下文，或者你可以從第一次DB拉後拆下答案，然後在保存中重新附加它。

但是，我認爲你有一個更基本的問題。你確定讓一個班級能夠創建自己的上下文並保存自己是個好主意嗎？你會遇到這樣的問題。