using System;

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using NUnit.Framework;

public class Program

{

    public static void Main()

    {

        SomeObject so = new SomeObject { Destination = new Destination(123), Message = "hello world" };

        TestSerializationRoundTrip(so);

        Console.WriteLine("Round trip OK");

        TestConverter(123);

        Console.WriteLine("Converter OK");

    }

    private static void TestSerializationRoundTrip(SomeObject so)

    {

        Assume.That(so, Is.Not.Null);

        Assume.That(so.Destination, Is.Not.Null);

        var json = JsonConvert.SerializeObject(so);

        Console.WriteLine(json);

        var newObj = JsonConvert.DeserializeObject<SomeObject>(json);

        Assert.That(newObj, Is.Not.Null);

        Assert.That(newObj.Destination, Is.Not.Null);

        Assert.That(newObj.Destination.Id, Is.EqualTo(so.Destination.Id));

    }

​

    private static void TestConverter(int testValue)

    {

        var sut = new DestinationConverter();

        JsonReader reader = new JTokenReader(JToken.Parse(string.Format("{0}", testValue)));

        var obj = sut.ReadJson(reader, typeof(Destination), null, JsonSerializer.CreateDefault());

​

        var result = obj as Destination;

​

        Assert.That(result, Is.Not.Null);

        Assert.That(result, Is.InstanceOf<Destination>());

        Assert.That(result.Id, Is.EqualTo(testValue));

    }

}

​

public class SomeObject

{

    [JsonProperty("destination")]

    public Destination Destination { get; set; }

    [JsonProperty("message")]

    public string Message { get; set; }

}

​

[JsonConverter(typeof(DestinationConverter))]

public class Destination

{

    public Destination (int destinationId)

    {

        Id = destinationId;

    }

    public int Id { get; private set;}

}

​

public class DestinationConverter : JsonConverter

{

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)

    {

        if (value is Destination)

        {

            Destination destination = value as Destination;

            writer.WriteValue(destination.Id);

        }

    }

    public override bool CanConvert(Type objectType) 

    {

        return objectType == typeof(Destination);

    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)

    {

        var value = reader.Value;

​

        if (value is long)

        {

            long v = (long) value;

            return new Destination((int)v);

        }

​

        return null;

    }

}