using System;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

        // Change some of the property names (e.g. "Details" -> "xDetails") in the JSON to see how the output changes.

        string json = @"

            {

              ""ID"": ""abc123"",

              ""Details"": {

                ""FirstName"": ""John"",

                ""LastName"": ""Doe"",

                ""BirthDate"": ""1990-06-20""

              }

            }";

        var person = JsonConvert.DeserializeObject<Person>(json);

        Console.WriteLine("ID: " + person.ID);

        Console.WriteLine("ID Specified: " + person.IDSpecified);

        Console.WriteLine("Details Specified: " + person.DetailsSpecified);

        Console.WriteLine("FirstName: " + person.Details?.FirstName);

        Console.WriteLine("FirstName Specified: " + (person.Details?.FirstNameSpecified ?? false));

        Console.WriteLine("LastName: " + person.Details?.LastName);

        Console.WriteLine("LastName Specified: " + (person.Details?.LastNameSpecified ?? false));

        Console.WriteLine("BirthDate: " + person.Details?.BirthDate);

        Console.WriteLine("BirthDate Specified: " + (person.Details?.BirthDateSpecified ?? false));

    }

}

​

public class Person

{

    public string ID { get; set; }

    public bool IDSpecified { get; set; }

    public Details Details { get; set; }

    public bool DetailsSpecified { get; set; }

}

​

public class Details 

{

    public string FirstName { get; set; }

    public bool FirstNameSpecified { get; set; }

    public string LastName { get; set; }

    public bool LastNameSpecified { get; set; }

    public string BirthDate { get; set; }

    public bool BirthDateSpecified { get; set; }

}

​