https://stackoverflow.com/questions/58138793/system-text-json-jsonelement-toobject-workaround

CSharp · Console

/Program.cs

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.Buffers;

using System.Text.Json;
using System.Text.Json.Serialization;

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

//https://stackoverflow.com/questions/58138793/system-text-json-jsonelement-toobject-workaround

// Alternatively, you might use ArrayPoolBufferWriter<byte>() from Microsoft.Toolkit.HighPerformance.Buffers
//     using var bufferWriter = new ArrayPoolBufferWriter<byte>();
// https://docs.microsoft.com/en-us/dotnet/api/microsoft.toolkit.highperformance.buffers.arraypoolbufferwriter-1?view=win-comm-toolkit-dotnet-7.0
// https://github.com/CommunityToolkit/dotnet/blob/main/CommunityToolkit.HighPerformance/Buffers/ArrayPoolBufferWriter%7BT%7D.cs

	public static partial class JsonExtensions
	{
		public static T ToObject<T>(this JsonElement element, JsonSerializerOptions options = null)
		{
			var bufferWriter = new ArrayBufferWriter<byte>();
			using (var writer = new Utf8JsonWriter(bufferWriter))
				element.WriteTo(writer);
			return JsonSerializer.Deserialize<T>(bufferWriter.WrittenSpan, options);
		}

		public static T ToObject<T>(this JsonDocument document, JsonSerializerOptions options = null)
		{
			if (document == null)
				throw new ArgumentNullException(nameof(document));
			return document.RootElement.ToObject<T>(options);
		}		
	}

	public class GlossDef
	{
		public string para { get; set; }
		public List<string> GlossSeeAlso { get; set; }
	}

	public class GlossEntry
	{
		public string ID { get; set; }
		public string SortAs { get; set; }
		public string GlossTerm { get; set; }
		public string Acronym { get; set; }
		public string Abbrev { get; set; }
		public GlossDef GlossDef { get; set; }
		public string GlossSee { get; set; }
	}

	public class GlossList
	{
		public GlossEntry GlossEntry { get; set; }
	}

	public class GlossDiv
	{
		public string title { get; set; }
		public GlossList GlossList { get; set; }
	}

	public class SomeClass
	{
		public string title { get; set; }
		public GlossDiv GlossDiv { get; set; }
	}

    class TestClass
    {
        public static void Test()
        {
			var str = GetJson();
			
			using var jDoc = JsonDocument.Parse(str);
			
			var myClass = jDoc.RootElement.GetProperty("SomeProperty").ToObject<SomeClass>();
			
			var newJson = JsonSerializer.Serialize(myClass, new JsonSerializerOptions { WriteIndented = true });
			
			Console.WriteLine(newJson);
		}	
		
		static string GetJson()
		{
			var json = @"{
   ""SomeProperty"":{
      ""title"":""example glossary"",
      ""GlossDiv"":{
         ""title"":""S"",
         ""GlossList"":{
            ""GlossEntry"":{
               ""ID"":""SGML"",
               ""SortAs"":""SGML"",
               ""GlossTerm"":""Standard Generalized Markup Language"",
               ""Acronym"":""SGML"",
               ""Abbrev"":""ISO 8879:1986"",
               ""GlossDef"":{
                  ""para"":""A meta-markup language, used to create markup languages such as DocBook."",
                  ""GlossSeeAlso"":[
                     ""GML"",
                     ""XML""
                  ]
               },
               ""GlossSee"":""markup""
            }
         }
      }
   }
}
";
			return json;
		}
	}


	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.CodeBase.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;
		}
	}