https://stackoverflow.com/questions/61061584/ignoring-some-default-values-for-serialization

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/61061584/ignoring-some-default-values-for-serialization

	public enum Flavor : ulong { ValueNotSet, Cherry, Blueberry, Cheese }

	public class DanishInventory { public int QtyInStock; public Flavor Flavor; }

	public class EnumDefaultValueContractResolver : DefaultContractResolver
	{
		protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
		{
			var property = base.CreateProperty(member, memberSerialization);
			if (property.DefaultValueHandling == null)
			{
				if (property.PropertyType.IsEnum)
				{
					//For safety you could check here if the default value is named ValueNotSet and only set IgnoreAndPopulate in that case.
					//var defaultValue = Enum.ToObject(property.PropertyType, 0);
					//if (defaultValue.ToString() == "ValueNotSet")
					//{					
						property.DefaultValueHandling = DefaultValueHandling.IgnoreAndPopulate; // Or DefaultValueHandling.Ignore if you prefer
					//}
				}
			}

			return property;
		}
	}

    class TestClass
    {
        public static void Test()
        {
			var resolver = new EnumDefaultValueContractResolver();
			
			var settings = new JsonSerializerSettings { ContractResolver = resolver };
			
			foreach (Flavor flavor in Enum.GetValues(typeof(Flavor)))
			{
				var inventory  = new DanishInventory { Flavor = flavor };
				var json = JsonConvert.SerializeObject(inventory, settings);

				Console.WriteLine("json for Flavor={0}", json);
				
				var test2 = JsonConvert.DeserializeObject<DanishInventory>(json, settings);
				
				Assert.IsTrue((flavor == default(Flavor)) == !json.Contains(nameof(inventory.Flavor)));
				Assert.IsTrue(inventory.Flavor == test2.Flavor);
			}
		}	
	}

	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.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;
		}
	}