如何使用 ExpressMapper 映射递归嵌套对象

Question

我正在开发一个 Web 应用程序（首先是 EF6 代码），使用户能够填写评估。一个评价包含多个问题，一个问题包含多个子问题。每个子问题都有一个 "mapping feature"，使用户能够将一个子问题关联到另一个现有的子问题。

我有以下 Entity Framework 个模型（我删除了一些属性，因为我的示例不需要它们）

public class Question
{
    public int ID { get; set; }
    public string Name { get; set; }
    public virtual ICollection<SubQuestion> SubQuestions { get; set; }
}
public class SubQuestion
{
    public int ID { get; set; }
    public int QuestionID { get; set; }
    public virtual Question Question { get; set; }

    [Required]
    [MaxLength(255)]
    public string Name { get; set; }
    public virtual ICollection<Answer> Answers { get; set; }

    //These 2 properties are used to create a many-to-many table for the mapping of subquestions
    //Automatic name = SubQuestion_ID
    //Subquestion of current evaluation to map to another evaluation
    public virtual ICollection<SubQuestion> SubquestionCurrentMapping { get; set; }

    //Automatic name = SubQuestion_ID1
    //Subquestion of evaluation the current evaluation is mapped to
    public virtual ICollection<SubQuestion> SubquestionPreviousMapping { get; set; }

}

在项目中我们使用了以下 DTO 对象

public class QuestionVM
{
    public int ID { get; set; }
    public string Name { get; set; }
    public List<SubQuestionVM> SubQuestions { get; set; } = new List<SubQuestionVM>();
}

public class SubQuestionVM
{
    public int ID { get; set; }
    public int QuestionID { get; set; }
    public string Name { get; set; }
    public List<AnswerVM> Answers { get; set; }

    public List<SubQuestionVM> SubquestionCurrentMapping { get; set; }
}

我们正在使用 ExpressMapper（参见 http://expressmapper.org）。我们有一种方法可以将所有 DTO 与 EF 模型进行映射，如下所示：

public void MappingRegistration()
{
    Mapper.Register<Question, QuestionVM>();
    Mapper.Register<SubQuestion, SubQuestionVM>();
    Mapper.Compile();
}

一切都已映射并且工作正常，直到我在子问题 VM 中添加以下属性：

public List<SubQuestionVM> SubquestionCurrentMapping { get; set; }

这属性创建一个多对多 table 到 link 的子问题一起用于映射功能。

当我尝试启动应用程序时，出现以下错误：

"Exception of type 'System.WhosebugException' was thrown."

我尝试的改变是：在 SubquestionVM

//public List<SubQuestionVM> SubquestionCurrentMapping { get; set; }                                                                         
public List<SubQuestionMappedVM> SubquestionCurrentMapping { get; set; } = new List<SubQuestionMappedVM>(); //Trying to fix by changing vm

有我要测试的新虚拟机：

public class SubQuestionMappedVM
{
    public int ID { get; set; }
    public int QuestionID { get; set; }
    public string Name { get; set; }
    //Remove this property, don't need more than 1 level of recursion anyway
    //public List<SubQuestionMappedVM> SubquestionCurrentMapping { get; set; }
    public List<AnswerVM> Answers { get; set; }
}

我还将新 VM 添加到执行映射的方法中：

Mapper.Register<SubQuestion, SubQuestionMappedVM>();

我认为我的问题是因为我正在映射一个 subquestionVM，其中包含创建递归的 subquestionVM 列表。我试图创建一个不同的 subquestionVM 来绕过这个问题，但我的网页甚至没有显示在我的浏览器中。在漫长的 1 分钟 45 之后，Visual Studio 回复 "A task was canceled."。

如果有人知道如何映射我的递归 SubquestionVM、如何使用不同的 VM 来停止递归或任何其他防止堆栈溢出错误的解决方案，我将不胜感激！

Answer 1

我是这样解决这个问题的：

我不知道如何使用 ExpressMapper 或不同的视图模型来绕过堆栈溢出异常，所以我创建了一个方法来执行从 EF 模型到 DTO 模型的手动映射。

/// <summary>
/// Map list of SubquestionVM (SubquestionCurrentMapping) with data from current Component (EF model).
/// 
/// Why are we doing this?
///     Because when using the ExpressMapping to map 'SubQuestion' to 'SubQuestionVM', it creates a stack overflow error on the property 'SubquestionCurrentMapping'
///     which is caused by recursive VM.
///     I originaly tried alternative solution like:
///         changing 'List<SubQuestionVM>' for 'List<SubQuestionMappedVM>' but the website was not even loading (even with proper value in the new VM, and global.asax),
///         loading the faulty property later on, but any attempt to populate the object was resulting in an overflow at a moment or another.
///     Thankfully the manual mapping is proven to be effective and errorless!
/// </summary>
/// <param name="evaluationVM"></param>
/// <param name="component"></param>
private static void ManualMappingOfRecursiveSubquestionVM(CurrentEvaluationVM evaluationVM, Component component)
{
    foreach (var subquestion in component?.Question?.SubQuestions)
    {
        //Find corresponding subquestionVM and manually map them
        var subquestionVM = evaluationVM.CurrentComponent?.Question?.SubQuestions.Find(s => s.ID == subquestion.ID);

        foreach (var subquestionMapping in subquestion.SubquestionCurrentMapping.ToList())
        {
            var tempSubquestionVM = new SubQuestionVM
            {
                ID = subquestionMapping.ID,
                QuestionID = subquestionMapping.QuestionID,
                Name = subquestionMapping.Name,
                Clarification = subquestionMapping.Clarification,
                Description = subquestionMapping.Description,
                Index = subquestionMapping.Index,
                CanSelectGoal = subquestionMapping.CanSelectGoal,
                IsDate = subquestionMapping.IsDate,
                Deprecated = subquestionMapping.Deprecated,
                MultipleChoices = subquestionMapping.MultipleChoices.Map<ICollection<MultipleChoice>, List<MultipleChoiceVM>>(),
                Answers = subquestionMapping.Answers.Map<ICollection<Answer>, List<AnswerVM>>()
            };
            subquestionVM.SubquestionCurrentMapping.Add(tempSubquestionVM);
        }
    }
}

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