https://stackoverflow.com/questions/76558333/jsonconvert-deserializeobject-throwing-error-after-adding-addnewtonsoftjson

CSharp · Console

/Program.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;

using System.ComponentModel.DataAnnotations;

using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using Newtonsoft.Json.Converters;
using Newtonsoft.Json.Serialization;	

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

//https://stackoverflow.com/questions/76558333/jsonconvert-deserializeobject-throwing-error-after-adding-addnewtonsoftjson

	public class ValidationResultConverter : JsonConverter<ValidationResult>
	{
		record DTO(string ErrorMessage, IEnumerable<string> MemberNames);		
		public override ValidationResult ReadJson(JsonReader reader, Type objectType, ValidationResult existingValue, bool hasExistingValue, JsonSerializer serializer) =>
			serializer.Deserialize<DTO>(reader) is {} dto
				? new ValidationResult(dto.ErrorMessage, dto.MemberNames)
				: null;
		public override void WriteJson(JsonWriter writer, ValidationResult value, JsonSerializer serializer) => 
			serializer.Serialize(writer, new DTO(value.ErrorMessage, value.MemberNames));
	}

	public class Mymodel
	{
		public List<ValidationResult> ValidationResults { get; } = new ();
	}

    class TestClass
    {
        public static void Test()
        {
			var model = new Mymodel
			{
				ValidationResults = 
				{
					new ("message1"),
					new ("message2", new [] { "member name 2.1", "member name 2.2" }),
				}
			};
			
			var settings = new JsonSerializerSettings
			{
				Converters = { new ValidationResultConverter() },
			};
			
			var res = JsonConvert.SerializeObject(model, Formatting.Indented, settings);
			Console.WriteLine(res);
			
			var validationResponse = JsonConvert.DeserializeObject<Mymodel>(res, settings);

			Assert.That(model.ValidationResults.Select(v => v.ErrorMessage).SequenceEqual(validationResponse.ValidationResults.Select(v => v.ErrorMessage)));
			Assert.That(model.ValidationResults.SelectMany(v => v.MemberNames).SequenceEqual(validationResponse.ValidationResults.SelectMany(v => v.MemberNames)));
			
			Assert.That(res == JsonConvert.SerializeObject(validationResponse, Formatting.Indented, settings));
		}	
	}

	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("{0} version: {1}", typeof(JsonSerializer).Namespace, typeof(JsonSerializer).Assembly.FullName);
			Console.WriteLine();

			try
			{
				TestClass.Test();
			}
			catch (Exception ex)
			{
				Console.WriteLine("Failed with unhandled exception: ");
				Console.WriteLine(ex);
				throw;
			}
		}
	}