实体类型“X”的属性“XID”是键的一部分，因此无法修改

Question

在新的 Blazor 项目中使用 EF-Core Code First。这是我第一次使用 EF 的核心版本，所以也许我错过了一些新的东西？

我有三个表/模型 - Questions、QuestionOptions 和 QuestionAnswers。 QuestionOptions 与 Questions 和 Answers 表相关，每个问题可以有多个选项，Answer 表可以存储 QuestionOptions 之一。

public class Question
{
    public int QuestionId { get; set; }
    public string QuestionText { get; set; }
    public bool Active { get; set; }
    public bool Required { get; set; }
    public bool AskToExplain { get; set; }
    public string TextToAskToExplain { get; set; } 

    public virtual int QuestionTypeId { get; set; }
    public virtual QuestionType QuestionType { get; set; }

    public virtual ICollection<QuestionOption> QuestionOptions { get; set; }

    public virtual ICollection<QuestionAnswer> QuestionAnswers { get; set; }
}

public class QuestionOption
{
    public int QuestionOptionId { get; set; }
    public string OptionText { get; set; }

    public virtual int QuestionId { get; set; }
    public virtual Question Question { get; set; }

    public virtual ICollection<QuestionAnswer> QuestionAnswers { get; set; }
}

public class QuestionAnswer
{
    public int QuestionAnswerId { get; set; }
    public string AnswerText { get; set; }

    public virtual int? QuestionOptionId { get; set; }
    public virtual QuestionOption? QuestionOption { get; set; }        

    public virtual int QuestionId { get; set; }
    public virtual Question Question { get; set; }

    public virtual int ProfileID { get; set; }
    public virtual Profile Profile { get; set; }
}

在 QuestionAnswers 表中插入一行可以正常工作，但更新会引发此错误：

实体类型“QuestionOption”上的属性“QuestionOptionId”是 键的一部分，因此不能修改或标记为已修改。到 更改具有可识别外国实体的现有实体的委托人 键首先删除依赖并调用'SaveChanges'然后关联 新委托人的受抚养人。

    public QuestionAnswer SaveAnswer(QuestionAnswer answer)
    {
        var chosenOption = _db.QuestionOptions.Find(answer.QuestionOptionId);
        var profile = _db.Profiles.Find(answer.Profile.ProfileID);
        var question = _db.Questions.Find(answer.Question.QuestionId);

        if (answer.QuestionAnswerId == 0)
        {   //this works fine...
            var newAnswer = new QuestionAnswer()
            {
                AnswerText = answer.AnswerText,
                QuestionOption = chosenOption,
                Profile = profile,
                Question = question
            };

            var addedEntity = _db.QuestionAnswers.Add(newAnswer);
            _db.SaveChanges();
            return addedEntity.Entity;
        }
        else
        {
            // This is where the error happens...
            var existingAnswer = _db.QuestionAnswers.Find(answer.QuestionAnswerId);
            existingAnswer.AnswerText = answer.AnswerText;
            existingAnswer.QuestionOption = chosenOption;
            _db.SaveChanges(); //<-- Error thrown here
            return existingAnswer;
        }
    }

错误消息听起来像是我正在尝试更改 QuestionOption 的主键，但实际上我只是在尝试更改 QuestionAnswer 指向的 QuestionOption。我只是想让它基本上运行这个 SQL：

 UPDATE QuestionAnswer
 SET AnswerText = @NewAnswerText, QuestionOptionId = @NewQuestionOptionId
 WHERE QuestionAnswerId = @QuestionAnswerId

我做错了什么？

提前感谢您的帮助。

Answer 1

不保证，但您可以尝试设置 FK existingAnswer.QuestionOptionId = answer.QuestionOptionId 而不是设置相关实体​​。这就是您将在数据库中执行的操作。