https://stackoverflow.com/questions/74624508/custom-json-net-json-converter-with-nested-objects

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 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/74624508/custom-json-net-json-converter-with-nested-objects

	public class WrapWithValueContractResolver : DefaultContractResolver
	{
        protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
        {
            var property = base.CreateProperty(member, memberSerialization);
			if (property.Converter == null && property.ItemConverter == null) // property.Converter check is required to avoid applying the converter to WrapWithValueConverter<TValue>.DTO.value
				property.Converter = (JsonConverter)Activator.CreateInstance(typeof(WrapWithValueConverter<>).MakeGenericType(property.PropertyType));
			return property;
        }
	}
	
	public class WrapWithValueConverter<TValue> : JsonConverter
	{
		// Here we take advantage of the fact that a converter applied to a property has highest precedence to avoid an infinite recursion.
		sealed class DTO { [JsonConverter(typeof(NoConverter)), JsonProperty(ReferenceLoopHandling  = ReferenceLoopHandling.Serialize)] public TValue value { get; set; } public object GetValue() => value; }

		public override bool CanConvert(Type objectType) => typeof(TValue).IsAssignableFrom(objectType);

		public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
			=> serializer.Serialize(writer, new DTO { value = (TValue)value });

		public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
			=> serializer.Deserialize<DTO>(reader)?.GetValue();
	}

	public class NoConverter : JsonConverter
	{
		// NoConverter taken from this answer https://stackoverflow.com/a/39739105/3744182
		// By https://stackoverflow.com/users/3744182/dbc
		// To https://stackoverflow.com/questions/39738714/selectively-use-default-json-converter
		public override bool CanConvert(Type objectType)  { throw new NotImplementedException(); /* This converter should only be applied via attributes */ }
		public override bool CanRead => false;
		public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer) => throw new NotImplementedException();
		public override bool CanWrite => false;
		public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer) => throw new NotImplementedException();
	}

	public class SalesOrder
	{
		[JsonProperty("project", NullValueHandling = NullValueHandling.Ignore)]
		public int? Project { get; set; }

		[JsonProperty("printDescriptionOnInvoice", NullValueHandling = NullValueHandling.Ignore)]
		public bool PrintDescriptionOnInvoice { get; set; }

		[JsonProperty("printNoteOnExternalDocuments", NullValueHandling = NullValueHandling.Ignore)]
		public bool PrintNoteOnExternalDocuments { get; set; }

		[JsonProperty("printNoteOnInternalDocuments", NullValueHandling = NullValueHandling.Ignore)]
		public bool PrintNoteOnInternalDocuments { get; set; }

		[JsonProperty("soBillingContact", NullValueHandling = NullValueHandling.Ignore)]
		public Contact SoBillingContact { get; set; }
	}

	public class Contact
	{
		[JsonProperty("overrideContact", NullValueHandling = NullValueHandling.Ignore)]
		public bool OverrideContact { get;set; }

		[JsonProperty("attention", NullValueHandling = NullValueHandling.Ignore)]
		public string Attention { get; set; }

		[JsonProperty("email", NullValueHandling = NullValueHandling.Ignore)]
		public string Email { get; set; }

		[JsonProperty("fax", NullValueHandling = NullValueHandling.Ignore)]
		public string Fax { get; set; }

		[JsonProperty("name", NullValueHandling = NullValueHandling.Ignore)]
		public string Name { get; set; }

		[JsonProperty("phone1", NullValueHandling = NullValueHandling.Ignore)]
		public string Phone1 { get; set; }

		[JsonProperty("phone2", NullValueHandling = NullValueHandling.Ignore)]
		public string Phone2 { get; set; }

		[JsonProperty("web", NullValueHandling = NullValueHandling.Ignore)]
		public string Web { get; set; }
	}

	class TestClass
	{
		public static void Test()
		{
			DefaultContractResolver resolver = new WrapWithValueContractResolver // Cache statically and reuse for best performance
			{
				//NamingStrategy = new CamelCaseNamingStrategy(), // Uncomment if you need camel case
			}; 
			
			Test(resolver);
			Test(null);
		}
		
		static void Test(IContractResolver resolver)
		{
			if (resolver == null)
				Console.WriteLine("\nTesting with no resolver:");
			else
				Console.WriteLine("\nTesting with contract resolver {0}:", resolver);
			
			var vSalesOrder = new SalesOrder()
			{
				Project = 1,
				PrintDescriptionOnInvoice = true,
				PrintNoteOnExternalDocuments = true,
				SoBillingContact = new Contact
				{
					Attention = "attention",
					Email = "@whatever.se",
					Fax = "lolfax"
				}
			};
			
			var settings = new JsonSerializerSettings
			{
				ContractResolver = resolver,
			};
			
			var json = JsonConvert.SerializeObject(vSalesOrder, Formatting.Indented, settings);
			
			Console.WriteLine(json);
			
			var order2 = JsonConvert.DeserializeObject<SalesOrder>(json, settings);
			
			var json2 = JsonConvert.SerializeObject(order2, Formatting.Indented, settings);
			
			Assert.AreEqual(json, json2);
			
			Assert.AreEqual(vSalesOrder.Project, order2.Project);
			Assert.AreEqual(vSalesOrder.PrintDescriptionOnInvoice, order2.PrintDescriptionOnInvoice);
			Assert.AreEqual(vSalesOrder.PrintNoteOnExternalDocuments, order2.PrintNoteOnExternalDocuments);
			Assert.AreEqual(vSalesOrder.SoBillingContact.Attention, order2.SoBillingContact.Attention);
			Assert.AreEqual(vSalesOrder.SoBillingContact.Email, order2.SoBillingContact.Email);
			Assert.AreEqual(vSalesOrder.SoBillingContact.Fax, order2.SoBillingContact.Fax);
		}
	}

	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;
			}
		}
	}