"An entity object cannot be referenced by multiple instances of IEntityChangeTracker in C#"

Question

需要这方面的帮助。我需要在控制器操作时将会话中的一些数据保存到数据库。但是我收到"实体对象不能被 C# 中的 IEntityChangeTracker 的多个实例引用"错误答。添加（答案）;

有人可以帮助我吗？

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);
                    }
                    }
                }

答案类 公开课答案 {

    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

你的问题是你从一个上下文中调用答案：

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

然后尝试使用答案类中的其他方法保存它：

  SADEntitiesContext db = new SADEntitiesContext();

解决问题的最快方法是能够在 Answer 类中设置上下文，这样您就不会跳转上下文，或者您可以在第一次从数据库中提取答案后分离答案，然后在保存中重新附加它。

但是，我认为您有一个更根本的问题。 您确定让类能够创建自己的上下文并保存自己是个好主意吗？ 你到处都会遇到这样的问题。