using System;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

        var a = new A { Id = "1" };

        var b = new B { Id = 1 };

        var aserialized = JsonConvert.SerializeObject(a);

        var bserialized = JsonConvert.SerializeObject(b);

        var AA = JsonConvert.DeserializeObject<A>(aserialized);

        var AB = JsonConvert.DeserializeObject<A>(bserialized);

        Console.WriteLine(AA.Id);

        Console.WriteLine(AB.Id);

        var BA = JsonConvert.DeserializeObject<B>(aserialized);

        var BB = JsonConvert.DeserializeObject<B>(bserialized);

        Console.WriteLine(BA.Id);

        Console.WriteLine(BB.Id);

    }

}

​

public class A

{

    public string Id { get; set; }

}

​

public class B

{

    public long? Id { get; set; }

}

​