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)
{
}
}
}

:webApiConfig.cs

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,"IerException":{"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()"}}