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 System.Text.Json.Serialization.Metadata;

​

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

​

//https://stackoverflow.com/questions/58074304/is-polymorphic-deserialization-possible-in-system-text-json/

public abstract class BaseType { } // Properties omitted

​

public class DerivedType1 : BaseType { public string Derived1 { get; set; } } 

public class DerivedType2 : BaseType { public int Derived2 { get; set; } }

​

public class DerivedType3 : BaseType { public string Derived3 { get; set; } } 

​

class TestClass

{

    public static void Test()

    {

        var list = new List<BaseType> { new DerivedType1 { Derived1 = "value 1" } };

​

        var resolver = new DefaultJsonTypeInfoResolver

        {

            Modifiers =

            {

                // Add an Action<JsonTypeInfo> modifier that sets up the polymorphism options for BaseType

                static typeInfo =>

                {

                    if (typeInfo.Type != typeof(BaseType))

                        return;

                    typeInfo.PolymorphismOptions = new()

                    {

                        DerivedTypes =

                        {

                            new JsonDerivedType(typeof(DerivedType1), "Derived1"),

                            new JsonDerivedType(typeof(DerivedType2), "Derived2")

                        }

                    };

                },

                // Add other modifiers as required.

            }

        };

        var options = new JsonSerializerOptions

        {

            TypeInfoResolver = resolver,

            // Add other options as required

        };          

​

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

​

        Console.WriteLine(json);

​

        Assert.That(json.Contains("value 1"));

​

        var list2 = JsonSerializer.Deserialize<List<BaseType>>(json, options);

​

        Assert.AreEqual(list2[0].GetType(), list[0].GetType());

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        var json2 = JsonSerializer.Serialize(list2, options);

​

        Assert.AreEqual(json, json2);

    }   

}

​

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;

        }

    }

}

​