using System;

using System.Collections.Generic;

using System.Linq;

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

public class Program

{

    public static void Main()

    {

        var obj = new

        {

            persons = new List<Person>

            {

                new Person

                {

                    Name = "John",

                    Surname = "Doe",

                    Address = new Address

                    {

                        Line1 = "Infinite Loop 1",

                        Line2 = "California"

                    }

                },

                new Person

                {

                    Name = "Jane",

                    Surname = "Doe",

                    Address = new Address

                    {

                        Line1 = "Infinite Loop 2",

                        Line2 = "California"

                    }

                }

            }

        };

​

        string json = JsonConvert.SerializeObject(obj, Formatting.Indented, new PersonConverter());

        Console.WriteLine(json);

    }

}

​

public class Person

{

    public string Name { get; set; }

    public string Surname { get; set; }

    public Address Address { get; set; }

}

​

public class Address

{

    public string Line1 { get; set; }

    public string Line2 { get; set; }

}

​

class PersonConverter : JsonConverter

{

    public override bool CanConvert(Type objectType)

    {

        return objectType == typeof(Person);

    }

​

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

    {

        var pairs = JObject.FromObject(value)

            .Descendants()

            .OfType<JProperty>()

            .Where(p => p.Value is JValue)

            .Select(p => p.Name + ":" + p.Value);

        writer.WriteValue(string.Join(",", pairs));

    }

​

    public override bool CanRead

    {

        get { return false; }

    }

​

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

    {

        throw new NotImplementedException();

    }

}

​