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/66495660/net-5-0-signature-change-of-system-text-json-jsonserializer-deserialize

​

#nullable enable

​

    //  Converter from https://stackoverflow.com/questions/63418549/custom-json-serializer-for-optional-property-with-system-text-json/

    //  With the fix for OptionalConverterInner<T>.Write() taken from https://stackoverflow.com/a/63431434/3744182

    [JsonConverter(typeof(OptionalConverter))]

    public readonly struct Optional<T>

    {

        public Optional(T value)

        {

            this.HasValue = true;

            this.Value = value;

        }

​

        public bool HasValue { get; }

        public T Value { get; }

        public static implicit operator Optional<T>(T value) => new Optional<T>(value);

        public override string ToString() => this.HasValue ? (this.Value?.ToString() ?? "null") : "unspecified";

    }

​

    public class Base

    {

        [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]

        public Optional<int?> Prop1 { get; set; }

        [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]

        public Optional<string?> Prop2 { get; set; }

        [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]

        public Optional<long?> Prop3 { get; set; }

    }

​

    public class Model

    {

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

​

    }

​

    public class OptionalConverter : JsonConverterFactory

    {

        public override bool CanConvert(Type typeToConvert)

        {

            if (!typeToConvert.IsGenericType) { return false; }

            if (typeToConvert.GetGenericTypeDefinition() != typeof(Optional<>)) { return false; }

            return true;

        }

​

        public override JsonConverter CreateConverter(Type typeToConvert, JsonSerializerOptions options)

        {

            Type valueType = typeToConvert.GetGenericArguments()[0];

​

            return (JsonConverter)Activator.CreateInstance(

                type: typeof(OptionalConverterInner<>).MakeGenericType(new Type[] { valueType }),

                bindingAttr: BindingFlags.Instance | BindingFlags.Public,

                binder: null,

                args: null,

                culture: null

            );

        }

​

        private class OptionalConverterInner<T> : JsonConverter<Optional<T>>

        {

            public override Optional<T> Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)

            {

                T value = JsonSerializer.Deserialize<T>(ref reader, options);

                return new Optional<T>(value);

            }

​

            // FIX taken from https://stackoverflow.com/a/63431434/3744182

            public override void Write(Utf8JsonWriter writer, Optional<T> value, JsonSerializerOptions options) =>

                JsonSerializer.Serialize(writer, value.Value, options);

        }

    }

​

    class TestClass

    {

        static Model GetModelInternal(bool baseOrDerived)

        {

            // Explicitly set null properties if baseOrDerived is false

            var item = baseOrDerived ? new Base { Prop2 = "hello" } : new Base { Prop1 = null, Prop2 = "hello", Prop3 = null };

            return new Model

            {

                Properties = new ()

                {

                    baseOrDerived ? new Base () : new Base { Prop1 = null, Prop2 = null, Prop3 = null },

                    item,

                },

            };

        }

        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;

            }

        }

    }

​