如何asp.net web api获取最后一个id？

Question

我使用了此代码段;

public IEnumerable<StdntInf> GetStdntInf()
    {
        int maxid = db.StdntInf.Max(m => m.StdntInfID);

        var sI = from n in db.StdntInf
                     where n.StdntInfID == maxid
                     select n;
        return sI;

    }

但是，此代码段异常..

Exception : 

{"Message":"An error has occurred.","ExceptionMessage":"The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; charset=utf-8'.","ExceptionType":"System.InvalidOperationException","StackTrace":null,"InnerException":{"Message":"An error has occurred.","ExceptionMessage":"Self referencing loop detected for property 'StdntInf' with type 'System.Data.Entity.DynamicProxies.StdntInf_8C7B5964BE0BCF23536487B4E4548AFAE3B31264D236BC395DE2120A20CA0E2D'. Path '[0].YktNmns[0]'.","ExceptionType":"Newtonsoft.Json.JsonSerializationException","StackTrace":"   konum: Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.CheckForCircularReference(JsonWriter writer, Object value, JsonProperty property, JsonContract contract, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n   konum: Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n   konum: Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n   konum: Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IWrappedCollection values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n   konum: Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n   konum: Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n   konum: Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n   konum: Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IWrappedCollection values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n   konum: Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n   konum: Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value)\r\n   konum: Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value)\r\n   konum: Newtonsoft.Json.JsonSerializer.Serialize(JsonWriter jsonWriter, Object value)\r\n   konum: System.Net.Http.Formatting.JsonMediaTypeFormatter.<>c__DisplayClassd.<WriteToStreamAsync>b__c()\r\n   konum: System.Threading.Tasks.TaskHelpe``rs.RunSynchronously(Action action, CancellationToken token)"}}