using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

​

using System.Text.Json;

using System.Text.Json.Serialization;

​

using NUnit.Framework; // Throws NUnit.Framework.AssertionException

​

//https://stackoverflow.com/questions/66495660/net-5-0-signature-change-of-system-text-json-jsonserializer-deserialize

​

#nullable enable

​

public class Base

{

  public int? Prop1 { get; set; }

  public string? Prop2 { get; set; }

  public long? Prop3 { get; set; }

}

​

public class Derived: Base 

{

  [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]

  public new int? Prop1 { get; set; }

  [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]

  public new string? Prop2 { get; set; }

  [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]

  public new long? Prop3 { get; set; }

}

​

    class TestClass

    {

        public static void Test()

        {

            var model = new Derived ();

​

            Console.WriteLine("JSON when serialized as {0}", nameof(Derived));

            Console.WriteLine(JsonSerializer.Serialize<Derived>(model));  // Outputs {}

​

            Console.WriteLine();

​

            Console.WriteLine("JSON when serialized as {0}", nameof(Base));

            Console.WriteLine(JsonSerializer.Serialize<Base>(model));     // Outputs {"Prop1":null,"Prop2":null,"Prop3":null} 

​

            Console.WriteLine();

​

            Console.WriteLine("JSON when serialized as {0}", nameof(System.Object));

            Console.WriteLine(JsonSerializer.Serialize<object>(model));     // Outputs {} 

        }   

    }

​

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: {0} ({1}), {2}", System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription , Environment.Version, Environment.OSVersion);

            Console.WriteLine("System.Text.Json version: " + typeof(JsonSerializer).Assembly.FullName);

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

                Console.WriteLine("Failed with unhandled exception: ");

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​