如何asp.net web api获取最后一个id？ [英] how to asp.net web api get for last id?

问题描述

我使用了此代码段;

I used this code snippet ;

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;

    }

例外：

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)"}}

推荐答案

试试此代码...

Try this code...

var qry = db.StdntInf
                     .OrderByDescending(m => m.StdntInfID) 
                     .FirstOrDefault(); 

参考 - 无法使用Json序列化Web API中的响应 [ ^ ]。

Refer - Failed to serialize the response in Web API with Json[^].

Quote：

当涉及从Web Api（或任何其他Web服务）将数据返回给使用者时，我强烈建议不要传回来自数据库的实体。使用模型可以更加可靠和可维护，您可以控制数据的外观，而不是数据库。

When it comes to returning data back to the consumer from Web Api (or any other web service for that matter), I highly recommend not passing back entities that come from a database. It is much more reliable and maintainable to use Models in which you have control of what the data looks like and not the database.

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