using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Reflection;

​

using System.Text.Json;

using System.Text.Json.Serialization;

​

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

​

//https://stackoverflow.com/questions/69201788/serialisation-of-custom-type-inheriting-dictionary-using-system-text-json-does-n#comment122310959_69201788

​

public class Product 

{

    public string ProductId { get; set; }

​

    [System.Text.Json.Serialization.JsonExtensionData]

    public Dictionary<string, object> Properties { get; set; } = new ();

​

    public Product(string productId) : base()

    {

        ProductId = productId;

    }

}

​

namespace Original

{

    public class Product : Dictionary<string, object>

    {

        public string ProductId { get; set; }

​

        public Product(string productId) : base()

        {

            ProductId = productId;

        }

    }

}

    class TestClass

    {

        public static void Test()

        {

            var p = new Product("ABC123");

            p.Properties["foo"] = "bar";

            var json = JsonSerializer.Serialize(p);

            Console.WriteLine(json);

            Assert.AreEqual(@"{""ProductId"":""ABC123"",""foo"":""bar""}", json);

            //Assert.Contains("productId", json, StringComparison.OrdinalIgnoreCase);

            var p2 = JsonSerializer.Deserialize<Product>(json);

            Assert.AreEqual(p.ProductId, p2.ProductId);

            var json2 = JsonSerializer.Serialize(p2);

            Assert.AreEqual(json, json2);

            var converter = new JsonSerializerOptions().GetConverter(typeof(Original.Product));

            Console.WriteLine("Converter used for {0}: {1}", typeof(Original.Product), converter);

        }

    }

​

    public class Program

    {

        public static void Main()

        {

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

            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;

            }

        }

        public static string GetNetCoreVersion()

        {

            //https://techblog.dorogin.com/how-to-detect-net-core-version-in-runtime-ecd65ad695be

            //

            var assembly = typeof(System.Runtime.GCSettings).GetTypeInfo().Assembly;

            var assemblyPath = assembly.Location.Split(new[] { '/', '\\' }, StringSplitOptions.RemoveEmptyEntries);

            int netCoreAppIndex = Array.IndexOf(assemblyPath, "Microsoft.NETCore.App");

            if (netCoreAppIndex > 0 && netCoreAppIndex < assemblyPath.Length - 2)

                return assemblyPath[netCoreAppIndex + 1];

            return "";

        }

    }

​