using System;

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var p1 = new Person(){ Id = 1, FirstName = "Thanh" };

        var p2 = new Person(){ Id = 1, LastName = "Truong Duc", Roles = new List<string>(){ "User" } };

        Person p3;

        MergeObject<Person>(p1, p2, out p3);

        Console.WriteLine(JsonConvert.SerializeObject(p3));

    }

    private static void MergeObject<T>(T obj1, T obj2, out T obj)

        {

            var properties = typeof(T).GetProperties();

            var objDefault = Activator.CreateInstance<T>();

            obj = Activator.CreateInstance<T>();

            foreach (var prop in properties)

            {

                var propValueDefault = prop.GetValue(objDefault);

                var propValue = prop.GetValue(obj1);

                Console.WriteLine(typeof(IEnumerable).IsAssignableFrom(prop.PropertyType));

                if(prop.PropertyType != typeof(string) && typeof(IEnumerable).IsAssignableFrom(prop.PropertyType)) // check prop is a collection

                {

                    Console.WriteLine("ok");

                    var propObj2Value = prop.GetValue(obj2) as IList;

                    if (propObj2Value != null)

                    {

                        if (propValue == null){

                            propValue = propObj2Value;

                        }else{

                            Console.WriteLine(JsonConvert.SerializeObject(propObj2Value));

                            Console.WriteLine(JsonConvert.SerializeObject(propValue));

                            foreach (var item in propObj2Value)

                            {

                                (propValue as IList).Add(item);

                            }

                        }

                        Console.WriteLine(JsonConvert.SerializeObject(propValue));

                    }

                }

                else

                {

                    if(propValue == propValueDefault)

                    {

                        propValue = prop.GetValue(obj2);

                    }

                }

                prop.SetValue(obj, propValue);

            }

        }

}

​

public class Person 

{

    public int Id { get; set; }

    public string FirstName { get; set; }

    public string LastName { get; set; }

    public string Address1 { get; set; }

    public string Address2 { get; set; }

    public List<string> Roles {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)

    {

        Person person = (Person)value;

        JObject result = new JObject();

        result.Add("id", person.Id);

        result.Add("fullname", (person.FirstName + " " + person.LastName).Trim());

        result.Add("address", (person.Address1 + " " + person.Address2).Trim());

        result.WriteTo(writer);

    }

​

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

    {

        JObject obj = JObject.Load(reader);

        Person person = new Person();

        person.Id = (int)obj["id"];   // assuming id will always be present in the JSON

        string fullName = (string)obj["fullname"];

        if (fullName != null)

        {

            string[] parts = fullName.Split(new char[] { ' ' }, 2);

            // if there's only 1 part, I'm assuming it is the first name

            if (parts.Length > 0)

                person.FirstName = parts[0];

            if (parts.Length > 1)

                person.LastName = parts[1];

        }

        person.Address1 = (string)obj["address"];  // don't bother trying to split address

        return person;

    }

}