检测到自引用循环 - 从 WebApi 取回数据到浏览器

问题描述

我正在使用 Entity Framework，但在将父子数据传输到浏览器时遇到问题.这是我的课程:

I am using Entity Framework and having a problem with getting parent and child data to the browser. Here are my classes:

 public class Question
 {
    public int QuestionId { get; set; }
    public string Title { get; set; }
    public virtual ICollection<Answer> Answers { get; set; }
}

public class Answer
{
    public int AnswerId { get; set; }
    public string Text { get; set; }
    public int QuestionId { get; set; }
    public virtual Question Question { get; set; }
}

我正在使用以下代码返回问答数据:

I am using the following code to return the question and answer data:

    public IList<Question> GetQuestions(int subTopicId, int questionStatusId)
    {
        var questions = _questionsRepository.GetAll()
            .Where(a => a.SubTopicId == subTopicId &&
                   (questionStatusId == 99 ||
                    a.QuestionStatusId == questionStatusId))
            .Include(a => a.Answers)
            .ToList();
        return questions; 
    }

在 C# 方面，这似乎可行，但我注意到答案对象有对问题的引用.当我使用 WebAPI 将数据获取到浏览器时，我收到以下消息:

On the C# side this seems to work however I notice that the answer objects have references back to the question. When I use the WebAPI to get the data to the browser I get the following message:

ObjectContent`1"类型未能序列化内容类型application/json;"的响应正文；charset=utf-8'.

The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; charset=utf-8'.

检测到类型为Models.Core.Question"的属性question"的自引用循环.

Self referencing loop detected for property 'question' with type 'Models.Core.Question'.

这是因为问题有答案，而答案有对问题的引用吗?我看过的所有地方都建议在孩子身上提到父母，所以我不知道该怎么做.有人可以给我一些建议吗?

Is this because the Question has Answers and the Answers have a reference back to Question? All the places I have looked suggest having a reference to the parent in the child so I am not sure what to do. Can someone give me some advice on this.

推荐答案

这是因为问题有答案，而答案有参考回问题?

Is this because the Question has Answers and the Answers have a reference back to Question?

是的.无法序列化.

请参阅 Tallmaris 的答案和 OttO 的评论，因为它更简单并且可以全局设置.

GlobalConfiguration.Configuration.Formatters.JsonFormatter.SerializerSettings.Re‌​ferenceLoopHandling = ReferenceLoopHandling.Ignore;

旧答案:

将 EF 对象 Question 投影到您自己的中间对象或 DataTransferObject.然后这个Dto就可以序列化成功了.

Project the EF object Question to your own intermediate or DataTransferObject. This Dto can then be serialized successfully.

public class QuestionDto
{
    public QuestionDto()
    {
        this.Answers = new List<Answer>();
    } 
    public int QuestionId { get; set; }
    ...
    ...
    public string Title { get; set; }
    public List<Answer> Answers { get; set; }
}

类似:

public IList<QuestionDto> GetQuestions(int subTopicId, int questionStatusId)
{
    var questions = _questionsRepository.GetAll()
        .Where(a => a.SubTopicId == subTopicId &&
               (questionStatusId == 99 ||
                a.QuestionStatusId == questionStatusId))
        .Include(a => a.Answers)
        .ToList();

    var dto = questions.Select(x => new QuestionDto { Title = x.Title ... } );

    return dto; 
}

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