using System;

using System.Linq;

using System.Reflection;

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

public class Program

{

    public static void Main()

    {

        MyType mt = new MyType

        {

            JsonData = @"""Prop1"":""Value1"", ""Prop2"":""Value2"", ""Prop3"":""Value3""",

            OtherProperty = "foo"

        };

        string json = JsonConvert.SerializeObject(mt, Formatting.Indented);

        Console.WriteLine(json);

    }

}

​

​

class MyTypeConverter : JsonConverter

{

    public override bool CanConvert(Type objectType)

    {

        return objectType == typeof(MyType);

    }

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

    {

        MyType mt = (MyType)value;

        JObject jo = new JObject();

        if (!string.IsNullOrWhiteSpace(mt.JsonData))

        {

            // JsonData is assumed to contain pre-formatted, comma-separated, JSON properties

            jo.Add(JObject.Parse("{" + mt.JsonData + "}").Properties());

        }

        foreach (PropertyInfo prop in typeof(MyType).GetProperties()

                 .Where(p => p.CanRead && p.Name != "JsonData"))

        {

            object val = prop.GetValue(mt, null);

            jo.Add(prop.Name, val != null ? JToken.FromObject(val, serializer) : JValue.CreateNull());

        }

        jo.WriteTo(writer);

    }

    public override bool CanRead

    {

        get { return false; }

    }

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

    {

        throw new NotImplementedException();

    }

}

​

​

[JsonConverter(typeof(MyTypeConverter))]

class MyType

{

    public string JsonData { get; set; }

    public string OtherProperty { get; set; }

}

​

​