using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Runtime.Serialization.Formatters;

using System.IO;

using System.Data;

using System.ComponentModel.DataAnnotations;

using System.Globalization;

using System.Reflection;

using System.Collections.ObjectModel;

​

using System.Text.Json;

using System.Text.Json.Serialization;

​

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

​

//https://stackoverflow.com/questions/65261654/how-do-you-implement-system-text-json-serialization-referencehandler-preserve-in

​

    public class Node

    {

        public Node Next { get; set; }

    }

​

    class TestClass

    {

        public static void Test()

        {

            var node = new Node

            {

                Next = new Node { }

            };

            node.Next.Next = node;

​

            Assert.IsTrue(node.Next != node && node.Next.Next == node);

            var options = new JsonSerializerOptions

            {

                ReferenceHandler = ReferenceHandler.Preserve,

                WriteIndented = true

            };          

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

            Console.WriteLine(json);

            var node2 = JsonSerializer.Deserialize<Node>(json, options);

            Assert.IsTrue(node2.Next != node2 && node2.Next.Next == node2);

            var json2 = JsonSerializer.Serialize(node2, options);

            Assert.IsTrue(json == json2);

        }   

    }

​

    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 null;

        }

    }

​