https://stackoverflow.com/questions/66268617/c-sharp-newtonsoft-single-object-or-array-jsonconverter-not-working-no-errors

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.Collections.ObjectModel;

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/66268617/c-sharp-newtonsoft-single-object-or-array-jsonconverter-not-working-no-errors

public class DummyDataModel
{
    public List<SomeFile> someFile { get; } = new List<SomeFile>();
    public partial class SomeFile
    {
        public string name { get; set; } = "";

        [JsonConverter(typeof(SingleObjectOrArrayJsonConverter<SomeA>))]
        public List<SomeA> a { get; } = new List<SomeA>();
        //public SomeA a { get; set; } = new SomeA();
    }

    public partial class SomeA
    {
        public string asub { get; set; } = "";
        public string atracking { get; set; } = "";
        public string adate { get; set; } = "";
    }

    internal class SingleObjectOrArrayJsonConverter<T> : JsonConverter<List<T>> where T : class, new()
    {
        public override void WriteJson(JsonWriter writer, List<T> value, JsonSerializer serializer) =>
			// avoid possibility of infinite recursion by wrapping the List<T> with AsReadOnly()
            serializer.Serialize(writer, value.Count == 1 ? (object)value.Single() : value.AsReadOnly());

        public override List<T> ReadJson(JsonReader reader, Type objectType, List<T> existingValue, bool hasExistingValue, JsonSerializer serializer)
        {
			existingValue ??= new ();
            switch (reader.TokenType)
            {
				case JsonToken.StartObject: existingValue.Add(serializer.Deserialize<T>(reader)); break;
				case JsonToken.StartArray: serializer.Populate(reader, existingValue); break;
				default: throw new ArgumentOutOfRangeException($"Converter does not support JSON token type {reader.TokenType}.");
            };
			return existingValue;
        }
    }
}

    class TestClass
    {
        public static void Test()
        {
			var unitJSON = GetJson();
			
			DummyDataModel uTest = JsonConvert.DeserializeObject<DummyDataModel>(unitJSON);

			Console.WriteLine( $"Did Test:\n{JsonConvert.SerializeObject(uTest, Formatting.Indented)}" );
		}	
		
		static string GetJson()
		{
			return @"{
""somefile"": [
    {
        ""name"": ""Bob"",
        ""a"": {
            ""asub"": ""Bob"",
            ""atracking"": ""Bob"",
            ""adate"": "" Bob""
        }
    },
    {
        ""name"": ""Bob"",
        ""a"": [
            {
                ""asub"": ""Bob"",
                ""atracking"": ""Bob"",
                ""adate"": ""Bob""
            },
            {
                ""asub"": ""Bob"",
                ""atracking"": ""Bob"",
                ""adate"": ""Bob""
            }
        ]
    }
]
}
";
		}
	}

	public class Program
	{
		public static void Main()
		{
			Console.WriteLine("Environment version: {0} ({1})", System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription , GetNetCoreVersion());
			Console.WriteLine("{0} version: {1}", typeof(JsonSerializer).Assembly.GetName().Name,  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;
		}
	}