自引用循环检测 - 从获取的WebAPI回数据到浏览器 [英] Self referencing loop detected - Getting back data from WebApi to the browser

问题描述

我使用实体框架，并具有让父母与子女数据到浏览器的一个问题。这里是我的类：

 公共类问题
 {
    公众诠释QuestionId {搞定;组; }
    公共字符串名称{搞定;组; }
    公共虚拟的ICollection＆LT;应答和GT;答案{搞定;组; }
}公共类答
{
    公众诠释AnswerId {搞定;组; }
    公共字符串文本{搞定;组; }
    公众诠释QuestionId {搞定;组; }
    公共虚拟问题问题{搞定;组; }
}
 

我用下面的code归还问题和答案数据：

 公开的IList＆LT;问题＆GT; GetQuestions（INT subTopicId，诠释questionStatusId）
    {
        VAR问题= _questionsRepository.GetAll（）
            。凡（一个= GT; a.SubTopicId == subTopicId＆放大器;＆放大器;
                   （questionStatusId == || 99
                    a.QuestionStatusId == questionStatusId））
            .INCLUDE（一个= GT; a.Answers）
            .ToList（）;
        返回的问题;
    }
 

在C＃的一面，这似乎不过工作，我发现答案对象都引用回的问题。当我使用的WebAPI获取数据到浏览器，我得到了以下信息：

  

在'ObjectContent`1类型没有序列化内容类型应用程序/ JSON响应主体;字符集= UTF-8。

  
  

用型Models.Core.Question'财产'问题'检测自参考循环

这是因为该问题有答案和答案有一个参考回的问题？我看过的所有地方建议在有孩子家长一个参考，所以我不知道该怎么做。有人可以给我一些建议这一点。

解决方案

  

这是因为该问题有答案和解答有
  参照回的问题？

是的。它不能被序列化。

编辑：见Tallmaris的回答和奥多的评论，因为它更简单，可以设置全局

。<$p$p><$c$c>GlobalConfiguration.Configuration.Formatters.JsonFormatter.SerializerSettings.Re‌​ferenceLoopHandling = ReferenceLoopHandling.Ignore;

老答案：

该项目EF对象问题来自己的中级或DataTransferObject。这DTO可以被成功序列化。

 公共类QuestionDto
{
    公共QuestionDto（）
    {
        this.Answers =新的List＆LT;应答和GT;（）;
    }
    公众诠释QuestionId {搞定;组; }
    ...
    ...
    公共字符串名称{搞定;组; }
    公开名单＆LT;应答和GT;答案{搞定;组; }
}
 

是这样的：

 公开的IList＆LT; QuestionDto＆GT; GetQuestions（INT subTopicId，诠释questionStatusId）
{
    VAR问题= _questionsRepository.GetAll（）
        。凡（一个= GT; a.SubTopicId == subTopicId＆放大器;＆放大器;
               （questionStatusId == || 99
                a.QuestionStatusId == questionStatusId））
        .INCLUDE（一个= GT; a.Answers）
        .ToList（）;    VAR DTO = questions.Select（X =＆gt;新建QuestionDto {标题= x.Title ...}）;    返回DTO;
}
 

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; }
}

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; 
    }

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:

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

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

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.

解决方案

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

Yes. It cannot be serialized.

EDIT: See Tallmaris's answer and OttO's comment as it is simpler and can be set globally.

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

Old Answer:

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; }
}

Something like:

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; 
}

这篇关于自引用循环检测 - 从获取的WebAPI回数据到浏览器的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！