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; }

}

​

    public class Model

    {

        [JsonIgnore]

        public List<Base>? Properties { get; set; }

​

        [JsonPropertyName(nameof(Properties))] // Surrogate property for Properties with items declared as object

        public IEnumerable<object>? SerializedProperties => Properties?.AsEnumerable();

    }

​

    class TestClass

    {

        static Model GetModelInternal(bool baseOrDerived)

        {

            return new Model

            {

                Properties = new ()

                {

                    baseOrDerived ? new Derived() : new Base(),

                    baseOrDerived ? new Derived { Prop2 = "hello" } : new Base { Prop2 = "hello" },

                },

            };

        }

        public static void Test()

        {

            var options = new JsonSerializerOptions

            {

                WriteIndented = true,

            };

            Console.WriteLine("Serialized Model with baseOrDerived = false");

            Console.WriteLine(JsonSerializer.Serialize(GetModelInternal(false), options));

​

            Console.WriteLine();

            Console.WriteLine("Serialized Model with baseOrDerived = true");

            Console.WriteLine(JsonSerializer.Serialize(GetModelInternal(true), options));

        }   

    }

​

    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;

            }

        }

    }

​