سوال: تبدل نوع خروجی WebApi به json

EstateController که از نوع webapi هست :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;
using EstateProject.Models;
namespace EstateProject.Controllers
{
public class EstateController : ApiController
{
dbsmaeelpour db = new dbsmaeelpour();
// GET: api/Estate
public IEnumerable<Estate> Get()
{
retu db.Estates.ToList();
}
// GET: api/Estate/5
public string Get(int id)
{
retu "value";
}
// POST: api/Estate
public void Post([FromBody]string value)
{
}
// PUT: api/Estate/5
public void Put(int id, [FromBody]string value)
{
}
// DELETE: api/Estate/5
public void Delete(int id)
{
}
}
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Http.Headers;
using System.Web.Http;
namespace EstateProject
{
public static class WebApiConfig
{
public static void Register(HttpConfiguration config)
{
// Web API configuration and services
// Web API routes
config.MapHttpAttributeRoutes();
config.Routes.MapHttpRoute(
name: "DefaultApi",
routeTemplate: "api/{controller}/{id}",
defaults: new { id = RouteParameter.Optional }
);
config.Formatters.JsonFormatter.SupportedMediaType s.Add(new MediaTypeHeaderValue("text/html"));
}
}
}

خروجی :

{"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.InvalidOperationExcep tion","StackTrace":null,"InnerException":{"Message ":"An error has occurred.","ExceptionMessage":"Self referencing loop detected for property 'Province' with type 'System.Data.Entity.DynamicProxies.Province_4347BD C7FBFE4F2E35F21AA902D09E8CA1F6E75FD2BB5ECA2D5F360C 0BA25CB1'. Path '[0].Province.Cities[0]'.","ExceptionType":"Newtonsoft.Json.JsonSerializa tionException","StackTrace":" at Newtonsoft.Json.Serialization.JsonSerializerInte alWriter.CheckForCircularReference(JsonWriter writer, Object value, JsonProperty property, JsonContract contract, JsonContainerContract containerContract, JsonProperty containerProperty) at Newtonsoft.Json.Serialization.JsonSerializerInte alWriter.CalculatePropertyValues(JsonWriter writer, Object value, JsonContainerContract contract, JsonProperty member, JsonProperty property, JsonContract& memberContract, Object& memberValue) at Newtonsoft.Json.Serialization.JsonSerializerInte alWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty) at Newtonsoft.Json.Serialization.JsonSerializerInte alWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty) at Newtonsoft.Json.Serialization.JsonSerializerInte alWriter.SerializeList(JsonWriter writer, IEnumerable values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty) at Newtonsoft.Json.Serialization.JsonSerializerInte alWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty) at Newtonsoft.Json.Serialization.JsonSerializerInte alWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty) at Newtonsoft.Json.Serialization.JsonSerializerInte alWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty) at Newtonsoft.Json.Serialization.JsonSerializerInte alWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty) at Newtonsoft.Json.Serialization.JsonSerializerInte alWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty) at Newtonsoft.Json.Serialization.JsonSerializerInte alWriter.SerializeList(JsonWriter writer, IEnumerable values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty) at Newtonsoft.Json.Serialization.JsonSerializerInte alWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty) at Newtonsoft.Json.Serialization.JsonSerializerInte alWriter.Serialize(JsonWriter jsonWriter, Object value, Type objectType) at Newtonsoft.Json.JsonSerializer.SerializeInteal(J sonWriter jsonWriter, Object value, Type objectType) at Newtonsoft.Json.JsonSerializer.Serialize(JsonWrite r jsonWriter, Object value) at System.Net.Http.Formatting.BaseJsonMediaTypeFormat ter.WriteToStream(Type type, Object value, Stream writeStream, Encoding effectiveEncoding) at System.Net.Http.Formatting.JsonMediaTypeFormatter. WriteToStream(Type type, Object value, Stream writeStream, Encoding effectiveEncoding) at System.Net.Http.Formatting.BaseJsonMediaTypeFormat ter.WriteToStream(Type type, Object value, Stream writeStream, HttpContent content) at System.Net.Http.Formatting.BaseJsonMediaTypeFormat ter.WriteToStreamAsync(Type type, Object value, Stream writeStream, HttpContent content, TransportContext transportContext, CancellationToken cancellationToken)--- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowF orNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.Handle NonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter.GetRes ult() at System.Web.Http.WebHost.HttpControllerHandler.d__1 b.MoveNext()"}}