为什么在网页API返回具有一对多的关系会导致错误的实体？ [英] why In web api returning an entity that has a one to many relationship causes an error?

问题描述

家伙，我有一个一对多的关系称为用户同一个班级，结果
我在网络的API返回的用户一个实例get方法
它工作正常，只要我没有任何

 用户ID |名称
0 |一个
1 |乙朋友表（此表用于构建一对多的关系）USER_ID | Friend_ID
 1 | 0
 0 | 1
 

这是我的GetMethod

  [HTTPGET]
        公共Models.User进行身份验证（）
        {
            尝试
            {
                返回db.Users.SingleOrDefault（X =＆GT; x.ID == 0）;
            }
            抓住
            {
                返回null;
            }
        }
 

如果我得到并返回一个User实体然后我得到的打击误差

谁能帮我解决这个问题下面的错误？

  

{消息：发生错误，ExceptionMessage：在'ObjectContent`1类型没有序列化内容类型的响应正文文本/ html; charset=utf-8'.\",\"ExceptionType\":\"System.InvalidOperationException\",\"StackTrace\":null,\"InnerException\":{\"Message\":\"An发生错误，ExceptionMessage：自参考循环型检测'System.Data.Entity.DynamicProxies.Friend_E5C79F4736EB2750392FFC7061B18E9C12F15F9583409603C75C5D1B1F7358D4'.路径'Friends1[0].User.Friends'.\",\"ExceptionType\":\"Newtonsoft.Json.JsonSerializationException\",\"StackTrace\":\"在Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.CheckForCircularReference（JsonWriter作家，对象的值，JsonProperty财产，JsonContract合同，JsonContainerContract containerContract，JsonProperty containerProperty）\\ r \\ n在Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList（JsonWriter作家，IWrappedCollection值， JsonArrayContract合同，JsonProperty成员，JsonContainerContract collectionContract，JsonProperty containerProperty）\\ r \\ n在Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue（JsonWriter作家，对象的值，JsonContract valueContract，JsonProperty成员，JsonContainerContract containerContract，JsonProperty containerProperty）\\ r \\ n在Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject（JsonWriter作家，对象的值，JsonObjectContract合同，JsonProperty成员，JsonContainerContract collectionContract，JsonProperty containerProperty）\\ r \\ n在Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue（JsonWriter作家，对象的值，JsonContract valueContract，JsonProperty成员，JsonContainerContract containerContract，JsonProperty containerProperty）\\ r \\ n在Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject（JsonWriter作家，对象的值，JsonObjectContract合同，JsonProperty成员，JsonContainerContract collectionContract，JsonProperty containerProperty）\\ r \\ n在Newtonsoft .Json.Serialization.JsonSerializerInternalWriter.SerializeValue（JsonWriter作家，对象的值，JsonContract valueContract，JsonProperty成员，JsonContainerContract containerContract，JsonProperty containerProperty）\\ r \\ n在Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList（JsonWriter作家，IWrappedCollection值，JsonArrayContract合同，JsonProperty成员，JsonContainerContract collectionContract，JsonProperty containerProperty）\\ r \\ n在Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue（JsonWriter作家，对象的值，JsonContract valueContract，JsonProperty成员，JsonContainerContract containerContract，JsonProperty containerProperty）\\ r \\ n在Newtonsoft。 Json.Serialization.JsonSerializerInternalWriter.SerializeObject（JsonWriter作家，对象的值，JsonObjectContract合同，JsonProperty成员，JsonContainerContract collectionContract，JsonProperty containerProperty）\\ r \\ n在Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue（JsonWriter作家，对象的值，JsonContract valueContract， JsonProperty成员，JsonContainerContract containerContract，JsonProperty containerProperty）\\ r \\ n在Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize（JsonWriter jsonWriter，对象的值）\\ r \\ n在Newtonsoft.Json.JsonSerializer.SerializeInternal（JsonWriter jsonWriter，对象的值）\\ r \\ñ在Newtonsoft.Json.JsonSerializer.Serialize（jsonWriter jsonWriter，对象的值）\\ r \\ n在System.Net.Http.Formatting.JsonMediaTypeFormatter＆LT;> c__DisplayClassd.b__c（个）\\ r \\ n在的System.Threading。 Tasks.TaskHelpers.RunSynchronously（动作的动作，令牌的CancellationToken）}}

解决方案

尝试改变的WebAPI格式。在WebApiConfig.cs添加这些行：

  VAR JSON = config.Formatters.JsonFormatter;
json.SerializerSettings preserveReferencesHandling = Newtonsoft.Json preserveReferencesHandling.Objects。;
config.Formatters.Remove（config.Formatters.XmlFormatter）;
 

和添加此行：

  json.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore
 

Guys I have a One to many relation to same class called user,
I am returning one instance of user in web apis get method it works fine as far as I don't have any

User 

ID  | Name 
0   | A 
1   | B 

Friends Table ( This table is used to build the one to many relationship ) 

User_ID | Friend_ID 
 1      |     0 
 0      |     1 

This is my GetMethod

[HttpGet]
        public Models.User   Authenticate()
        {
            try
            {
                return   db.Users.SingleOrDefault(x => x.ID == 0 ) ; 
            } 
            catch
            {
                return null;
            }
        }

If I get and return a User entity then I get the blow error

Can anyone please help me to fix this below error ?

{"Message":"An error has occurred.","ExceptionMessage":"The 'ObjectContent`1' type failed to serialize the response body for content type 'text/html; charset=utf-8'.","ExceptionType":"System.InvalidOperationException","StackTrace":null,"InnerException":{"Message":"An error has occurred.","ExceptionMessage":"Self referencing loop detected with type 'System.Data.Entity.DynamicProxies.Friend_E5C79F4736EB2750392FFC7061B18E9C12F15F9583409603C75C5D1B1F7358D4'. Path 'Friends1[0].User.Friends'.","ExceptionType":"Newtonsoft.Json.JsonSerializationException","StackTrace":" at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.CheckForCircularReference(JsonWriter writer, Object value, JsonProperty property, JsonContract contract, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IWrappedCollection values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IWrappedCollection values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value)\r\n at Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value)\r\n at Newtonsoft.Json.JsonSerializer.Serialize(JsonWriter jsonWriter, Object value)\r\n at System.Net.Http.Formatting.JsonMediaTypeFormatter.<>c__DisplayClassd.b__c()\r\n at System.Threading.Tasks.TaskHelpers.RunSynchronously(Action action, CancellationToken token)"}}

解决方案

Try to change webApi formatter. Add these lines in WebApiConfig.cs:

var json = config.Formatters.JsonFormatter;
json.SerializerSettings.PreserveReferencesHandling = Newtonsoft.Json.PreserveReferencesHandling.Objects;
config.Formatters.Remove(config.Formatters.XmlFormatter);

And add this line:

json.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore

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