渴望在asp.net Web API中加載

Question

嗨，社區，我最近開始學習如何編寫網絡api，

我在winform中有一個項目想要使用Web api進行重新制作，但問題是我無法使用緊急加載，我總是收到錯誤500，代碼如下：

public HttpResponseMessage GetExpediente()
    {
        db.Configuration.ProxyCreationEnabled = false;
        var expediente = db.Expediente.Include(x=>x.Documento);
        if (expediente.Any())
        {
            return Request.CreateResponse(HttpStatusCode.OK, expediente);
        }
        else
        {
            return Request.CreateErrorResponse(HttpStatusCode.NotFound,
                "No se encontraron expedientes.");
        }
    }

我總是得到的錯誤是：

{"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 'Expediente' with type 'Modelo.Expediente'. Path '[0].Documento[0]'.","ExceptionType":"Newtonsoft.Json.JsonSerializationException","StackTrace":"   en Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.CheckForCircularReference(JsonWriter writer, Object value, JsonProperty property, JsonContract contract, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n   en Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.CalculatePropertyValues(JsonWriter writer, Object value, JsonContainerContract contract, JsonProperty member, JsonProperty property, JsonContract& memberContract, Object& memberValue)\r\n   en Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n   en Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n   en Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IEnumerable values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n   en Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n   en Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n   en Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n   en Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IEnumerable values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n   en Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n   en Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value, Type objectType)\r\n   en Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value, Type objectType)\r\n   en System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, Encoding effectiveEncoding)\r\n   en System.Net.Http.Formatting.JsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, Encoding effectiveEncoding)\r\n   en System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, HttpContent content)\r\n   en System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStreamAsync(Type type, Object value, Stream writeStream, HttpContent content, TransportContext transportContext, CancellationToken cancellationToken)\r\n--- Fin del seguimiento de la pila de la ubicación anterior donde se produjo la excepción ---\r\n   en System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   en System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   en System.Web.Http.WebHost.HttpControllerHandler.<WriteBufferedResponseContentAsync>d__1b.MoveNext()"}}

我一直在尋找信息。 那可以幫助我，但我總是發現我應該禁用延遲加載，但我確實做到了，但沒有成功，這里有人可以幫助我嗎？

順便說一句，我的目標是從Windows窗體項目中使用此api，有人告訴我這樣做：

var emp1 = response.Content.ReadAsStringAsync().Result;
        var result = JsonConvert.DeserializeObject<IEnumerable<ExpedientePOCO>>(emp1);

但是我從var emp1 = ...的行中得到的錯誤500。哦，當我從上下文中獲取include時，它的工作正常，但是我想使用Eager加載，希望對您有所幫助！

謝謝！ 問候！

我對DTO的了解：

 public HttpResponseMessage GetExpediente()
    {
        db.Configuration.ProxyCreationEnabled = false;
        var expediente = db.Expediente.Include(x=>x.Documento);
        List<ExpedientePOCO> expPOCO = new List<ExpedientePOCO>();
        foreach (var entidad in expediente)
        {
            String fecha = String.Format("{0:dd-MM-yyy}", entidad.FechaCreacion);
            ExpedientePOCO expedientePOCO = new ExpedientePOCO()
            {
                idExpediente = entidad.idExpediente,
                NombreExpediente = entidad.NombreExpediente,
                FechaCreacion = Convert.ToDateTime(fecha),
                DuenioExpediente = entidad.DuenioExpediente,
                CantidadDocumento = entidad.CantidadDocumento
            };
            foreach (var documentos in entidad.Documento)
            {
                DocumentoPOCO documento = new DocumentoPOCO()
                {
                    idDocumento = documentos.idDocumento,
                    idExpediente = documentos.idExpediente,
                    NombreDocumento = documentos.NombreDocumento,
                    FechaCreacion = documentos.FechaCreacion,
                    Expedientes = expedientePOCO
                };
                expedientePOCO.Documentos.Add(documento);
            }
            expPOCO.Add(expedientePOCO);
        }
        if (expPOCO.Any())
        {
            return Request.CreateResponse(HttpStatusCode.OK, expPOCO);
        }
        else
        {
            return Request.CreateErrorResponse(HttpStatusCode.NotFound,
                "No se encontraron expedientes.");
        }
    }

Answer 1

問題是，如錯誤消息所述，您有一個無限循環，很可能是這樣的：

public class A
{
    public B B { get; set; }
}

public class B
{
    public virtual ICollection<A> A { get; set; }
}

因此，您A => B => A無休止地得到A => B => A ，因此會出現錯誤。 您可以通過配置串行（解決這個ReferenceLoopHandling.Ignore ，或通過使用屬性（在NewtonSoft.Json） [JsonIgnore]根據您的具體需求和工具使用。

另一個解決方案是使用數據傳輸對象（DTO）或類似的方法：

public class ADTO
{
    // needed properties only
    public BDTO B { get; set; }
}

public class BDTO
{
    // needed properties only
    public List<ADTO> A { get; set; }
}

然后選擇DTO而不是實體：

var data = db.As
    .Select(a => new ADTO 
    {
        x = a.x ....
        B = new BDTO { x = a.B.x ...  }
    }
    .ToList();

或者，反過來：

var data = context.B
    .Select(b => new BDTO
    {
        x = b.x ...
        A = b.A
            .Select(a => new ADTO
            {
                x = a.x ...
            }
            .ToList()
    }
    .ToList();