using System;

using System.Collections.Generic;

using System.Linq;

using System.Reflection;

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

public class Program

{

    public static void Main()

    {

        List<Foo> foos = new List<Foo>

        {

            new Foo

            {

                Id = 1,

                Name = "A foo with a car",

                Item = new Vehicle

                {

                    Make = "Ford",

                    Model = "Mustang",

                    Year = 1965,

                }

            },

            new Foo

            {

                Id = 2,

                Name = "A foo holding a profile",

                Item = new Profile

                {

                    AccountName = "jschmoe",

                    DateCreated = DateTime.UtcNow

                }

            }

        };

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

        Console.WriteLine(json);

    }

}

​

​

[JsonConverter(typeof(DynamicPropertyNameConverter))]

class Foo

{

    public int Id { get; set; }

    public string Name { get; set; }

​

    [JsonPropertyNameByType("Vehicle", typeof(Vehicle))]

    [JsonPropertyNameByType("Profile", typeof(Profile))]

    public object Item { get; set; }

}

​

class Vehicle

{

    public string Make { get; set; }

    public string Model { get; set; }

    public int Year { get; set; }

}

​

class Profile

{

    public string AccountName { get; set; }

    public DateTime DateCreated { get; set; }

}

​

​

[AttributeUsage(AttributeTargets.Property, AllowMultiple = true)]

class JsonPropertyNameByTypeAttribute : Attribute

{

    public string PropertyName { get; set; }

    public Type ObjectType { get; set; }

    public JsonPropertyNameByTypeAttribute(string propertyName, Type objectType)

    {

        PropertyName = propertyName;

        ObjectType = objectType;

    }

}

​

​

public class DynamicPropertyNameConverter : JsonConverter

{

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

    {

        Type type = value.GetType();

        JObject jo = new JObject();

        foreach (PropertyInfo prop in type.GetProperties().Where(p => p.CanRead))

        {

            string propName = prop.Name;

            object propValue = prop.GetValue(value, null);

            JToken token = (propValue != null) ? JToken.FromObject(propValue, serializer) : JValue.CreateNull();

            if (propValue != null && prop.PropertyType == typeof(object))

            {

                JsonPropertyNameByTypeAttribute att = prop.GetCustomAttributes<JsonPropertyNameByTypeAttribute>()

                    .FirstOrDefault(a => a.ObjectType.IsAssignableFrom(propValue.GetType()));

                if (att != null)

                    propName = att.PropertyName;

            }

            jo.Add(propName, token);

        }

        jo.WriteTo(writer);

    }

    public override bool CanRead

    {

        get { return false; }

    }

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

    {

        // ReadJson is not called if CanRead returns false.

        throw new NotImplementedException();

    }

    public override bool CanConvert(Type objectType)

    {

        // CanConvert is not called if a [JsonConverter] attribute is used

        return false;

    }

}

​