EF關于報錯Self referencing loop detected with type的原因以及解決辦法
1）具體報錯

{
    "Message": "出現錯誤。",
    "ExceptionMessage": "“ObjectContent`1”類型未能序列化內容類型“application/json; charset=utf-8”的響應正文。",
    "ExceptionType": "System.InvalidOperationException",
    "StackTrace": null,
    "InnerException": {
        "Message": "出現錯誤。",
        "ExceptionMessage": "Self referencing loop detected for property 'auth_role' with type 'System.Data.Entity.DynamicProxies.auth_role_D04219A66C0CD8B839EF745B94309FF128B7C1D40C06E5BBBD55963530DFBAD1'. Path 'Data[1].auth_users[0]'.",
        "ExceptionType": "Newtonsoft.Json.JsonSerializationException",
        "StackTrace": "   在 Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.CheckForCircularReference(JsonWriter writer, Object value, JsonProperty property, JsonContract contract, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n   在 Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.CalculatePropertyValues(JsonWriter writer, Object value, JsonContainerContract contract, JsonProperty member, JsonProperty property, JsonContract& memberContract, Object& memberValue)\r\n   在 Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n   在 Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IEnumerable values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n   在 Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n   在 Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IEnumerable values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n   在 Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n   在 Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value, Type objectType)\r\n   在 Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value, Type objectType)\r\n   在 System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, Encoding effectiveEncoding)\r\n   在 System.Net.Http.Formatting.JsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, Encoding effectiveEncoding)\r\n   在 System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStreamAsync(Type type, Object value, Stream writeStream, HttpContent content, TransportContext transportContext, CancellationToken cancellationToken)\r\n--- 引發異常的上一位置中堆棧跟蹤的末尾 ---\r\n   在 System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   在 System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   在 System.Web.Http.WebHost.HttpControllerHandler.<WriteBufferedResponseContentAsync>d__1b.MoveNext()"
    }
}

2）分析可能原因

1）web api影響了返回序列化的問題？

2）返回json重復調用問題？

3）確定具體原因

結論：是web api自帶的return Json把模型間的導航屬性也算進去了。（A是B的導航屬性，B也是A的導航屬性，所以會無限循環，導致Json會生成無數層）

4）解決

1）修改泛型的返回值  改成標準的返回對象類（建議）

2）刪掉外鍵關聯【也就是刪除導航屬性】（不建議）

3）全局刪除循環引用 webapiconfig中修改如下：（高效）

config.Formatters.JsonFormatter.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore;

4）在導航屬性上加注解[JsonIgnore]忽略此屬性 ef采用db first的話不適用。（低效）