[Fork] [Fork] [Fork] [Fork] [Fork] [Fork] Json.NET Core Template Fiddle V2https://stackoverflow.com/questions/73817932/newtonsoft-json-has-a-deserialization-bug-when-class-has-quick-access-property

CSharp · Console

/Program.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
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/73817932/newtonsoft-json-has-a-deserialization-bug-when-class-has-quick-access-property

    public class Parent
    {
        public List<Child> Children { get; set; } = new List<Child>();

		[GetOnlyJsonProperty]
        public Child FirstChild => Children.First();
		
		public bool ShouldSerializeFirstChild() => Children != null && Children.Count > 0;
    }

    public class Child
    {
        public List<GrandChild> Children { get; set; } = new List<GrandChild>();
    }

    public class GrandChild
    {
        public string Value { get; set; }
    }

	[System.AttributeUsage(System.AttributeTargets.Property, AllowMultiple = false)]
	public class GetOnlyJsonPropertyAttribute : Attribute
	{
	}

	public class GetOnlyContractResolver : DefaultContractResolver
    {
		// From this answer https://stackoverflow.com/a/56885301/3744182
		// By https://stackoverflow.com/users/7027460/pavlo-lissov
		// To https://stackoverflow.com/questions/31731320/serialize-property-but-do-not-deserialize-property-in-json-net
        protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
        {
            var property = base.CreateProperty(member, memberSerialization);
            if (property != null) 
            {
                var attributes = property.AttributeProvider.GetAttributes(typeof(GetOnlyJsonPropertyAttribute), true);
                if (attributes != null && attributes.Count > 0)
                    property.ShouldDeserialize = (a) => false;  
            }
            return property;
        }
    }
	
    class TestClass
    {
        public static void Test()
        {
            var parent = new Parent
            {
                Children = new List<Child>
                {
                    new Child
                    {
                       Children = new List<GrandChild>
                        {
                            new GrandChild { Value = "I am a grand child" },
                        }
                    },
                    new Child(),
                }
            };

			IContractResolver resolver = new GetOnlyContractResolver(); // In production code this should be cached statically to improve performance
			var settings = new JsonSerializerSettings { ContractResolver = resolver };
			
            var serializedParent = JsonConvert.SerializeObject(parent, settings);
            var deserializedParent = JsonConvert.DeserializeObject<Parent>(serializedParent, settings);

            var reserializedParent = JsonConvert.SerializeObject(deserializedParent, settings);
			
			Console.WriteLine(serializedParent);
			Console.WriteLine(reserializedParent);
			
            // Expected: 1, Actual: 2
			Assert.AreEqual(parent.Children[0].Children.Count, deserializedParent.Children[0].Children.Count);
			
			Assert.AreEqual(serializedParent, reserializedParent);
			
			Assert.DoesNotThrow(() => JsonConvert.SerializeObject(new Parent (), 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;
			}
		}
	}