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/64552981/newtonsoft-json-defaultcontractresolver-remove-key-from-dictionary

​

// Converter

​

    public class KeyFilteringDictionaryConverter<TKey, TValue> : JsonConverter<IDictionary<TKey, TValue>>

    {

        readonly HashSet<TKey> toSkip;

        public KeyFilteringDictionaryConverter(IEnumerable<TKey> toSkip) => this.toSkip = toSkip?.ToHashSet() ?? throw new ArgumentNullException(nameof(toSkip));

​

        public override void WriteJson(JsonWriter writer, IDictionary<TKey, TValue> value, JsonSerializer serializer) => serializer.Serialize(writer, new KeyFilteringDictionarySurrogate<TKey, TValue>(value, toSkip));

        public override bool CanRead => false;

        public override IDictionary<TKey, TValue> ReadJson(JsonReader reader, Type objectType, IDictionary<TKey, TValue> existingValue, bool hasExistingValue, JsonSerializer serializer) => throw new NotImplementedException();

    }

​

    public class KeyFilteringDictionarySurrogate<TKey, TValue> : IReadOnlyDictionary<TKey, TValue>

    {

        readonly IDictionary<TKey, TValue> dictionary;

        readonly HashSet<TKey> toSkip;

​

        public KeyFilteringDictionarySurrogate(IDictionary<TKey, TValue> dictionary, IEnumerable<TKey> toSkip) : this(dictionary, toSkip ?.ToHashSet()) { }

        public KeyFilteringDictionarySurrogate(IDictionary<TKey, TValue> dictionary, HashSet<TKey> toSkip) 

        { 

            this.dictionary = dictionary ?? throw new ArgumentNullException(nameof(dictionary));

            this.toSkip = toSkip ?? throw new ArgumentNullException(nameof(toSkip));

        }

​

        public bool ContainsKey(TKey key) => !toSkip.Contains(key) && dictionary.ContainsKey(key);

        public bool TryGetValue(TKey key, out TValue value)

        {

            if (toSkip.Contains(key))

            {

                value = default(TValue);

                return false;

            }

            return dictionary.TryGetValue(key, out value); 

        }

        public TValue this[TKey key] => toSkip.Contains(key) ? throw new KeyNotFoundException() : dictionary[key];

        public IEnumerable<TKey> Keys => this.Select(p => p.Key);

        public IEnumerable<TValue> Values => this.Select(p => p.Value);

        public int Count => this.Count(); // Could be made faster?

        public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator() => dictionary.Where(p => !toSkip.Contains(p.Key)).GetEnumerator();

        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();

    }

​

// Resolver

​

    public class IgnorePrivatePropertiesContractResolver : DefaultContractResolver

    {

        protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)

        {

            var jsonProperties = base.CreateProperties(type, memberSerialization);

            // Apply to all string-keyed dictionary properties named "Data" that do not already have a converter

            foreach (var dataProperty in jsonProperties.Where(p => p.PropertyName == "Data" && p.Converter == null))

            {

                var keyValuePairTypes = dataProperty.PropertyType.GetDictionaryKeyValueTypes().ToList();

                if (keyValuePairTypes.Count == 1 && keyValuePairTypes[0][0] == typeof(string))

                {

                    // Filter all properties with PrivateFieldAttribute applied

                    var ignoreProperties = jsonProperties.Where(p => p.AttributeProvider.GetAttributes(typeof(PrivateFieldAttribute), true).Any()).Select(p => p.PropertyName).ToHashSet();

                    if (ignoreProperties.Count > 0)

                    {

                        dataProperty.Converter = (JsonConverter)Activator.CreateInstance(typeof(KeyFilteringDictionaryConverter<,>).MakeGenericType(keyValuePairTypes[0]), new object [] { ignoreProperties });

                    }

                }

            }

            return jsonProperties;

        }

    }

​

    public static class TypeExtensions

    {

        public static IEnumerable<Type> GetInterfacesAndSelf(this Type type)

            => (type ?? throw new ArgumentNullException()).IsInterface ? new[] { type }.Concat(type.GetInterfaces()) : type.GetInterfaces();

​

        public static IEnumerable<Type []> GetDictionaryKeyValueTypes(this Type type)

            => type.GetInterfacesAndSelf().Where(t => t.IsGenericType && t.GetGenericTypeDefinition() == typeof(IDictionary<,>)).Select(t => t.GetGenericArguments());

    }

​

    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Property, AllowMultiple=false)]

    public class PrivateFieldAttribute : System.Attribute { }

​

// Test Class

​

    public class Test

    {

        public Dictionary<string, string> Data;

​

        [PrivateField]

        [JsonIgnore]

        public string Name { get { return Data["Name"]; } set { Data.Add("Name", value); } }

​

        public string NotPrivate { get { return Data["NotPrivate"]; } set { Data.Add("NotPrivate", value); } }

    }

​

    class TestClass

    {

        public static void Test()

        {

            var test = new Test

            {

                Data = new Dictionary<string, string>

                {

                    {"SomeAdditionalKey", "Some additional value"},

                },

                Name = "private value",

                NotPrivate = "public value",

            };

            var resolver = new IgnorePrivatePropertiesContractResolver();

            var settings = new JsonSerializerSettings

            {

                ContractResolver = resolver,

            };

            var json = JsonConvert.SerializeObject(test, Formatting.Indented, settings);

            Console.WriteLine(json);

            Assert.IsTrue(!json.Contains("private value"));

            Assert.IsTrue(json.Contains("Some additional value"));

            Assert.IsTrue(json.Contains("public value"));

        }   

    }

​

    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;

        }

    }

​