using System;

using System.Linq;

using System.Collections.Generic;

using System.Text.Json;

using System.Text.Json.Serialization;

using System.Text.Json.Serialization.Metadata;

using System.Reflection;

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

​

var container = new Root<Base>

{

    Data = new ChildChild1 { BaseI = 42, ChildI = 777, ChildChildI = 1 }

};

​

var options = new JsonSerializerOptions

{

    WriteIndented = true, TypeInfoResolver = new DefaultJsonTypeInfoResolver { Modifiers = { AddNestedDerivedTypes } }

};

​

var json = JsonSerializer.Serialize(container, options);

var @base = JsonSerializer.Deserialize<Root<Base>>(json, options);

Console.WriteLine(@base.Data.GetType());

Assert.AreEqual(typeof(ChildChild1), @base.Data.GetType());

​

static void AddNestedDerivedTypes(JsonTypeInfo jsonTypeInfo)

{

    if (jsonTypeInfo.PolymorphismOptions is null) return;

​

    var derivedTypes = jsonTypeInfo.PolymorphismOptions.DerivedTypes

        .Where(t => t.DerivedType.GetCustomAttribute<JsonDerivedTypeAttribute>() != null).Select(t => t.DerivedType)

        .ToList();

    var hashset = new HashSet<Type>(derivedTypes);

    var queue = new Queue<Type>(derivedTypes);

    while (queue.TryDequeue(out var derived))

    {

        if (!hashset.Contains(derived))

            // Todo: handle discriminators

            jsonTypeInfo.PolymorphismOptions.DerivedTypes.Add(new JsonDerivedType(derived, derived.FullName));

​

        var attribute = derived.GetCustomAttributes<JsonDerivedTypeAttribute>();

        foreach (var jsonDerivedTypeAttribute in attribute) queue.Enqueue(jsonDerivedTypeAttribute.DerivedType);

    }

}

​

[JsonDerivedType(typeof(Child1))]

public class Base

{

    public int BaseI { get; set; }

}

​

[JsonDerivedType(typeof(ChildChild1))]

public class Child1 : Base

{

    public int ChildI { get; set; }

}

​

public class ChildChild1 : Child1

{

    public int ChildChildI { get; set; }

}

​

public class Root<T>

{

    public T Data { get; set; }

}