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 System.Text.Json;

using System.Text.Json.Serialization;

​

using NUnit.Framework; // Throws NUnit.Framework.AssertionException

​

//https://stackoverflow.com/questions/59644016/system-text-json-serialize-dictionary-as-array

​

    public class DictionaryConverterFactory : JsonConverterFactory

    {

        public override bool CanConvert(Type typeToConvert)

        {

            return typeToConvert.IsClass && typeToConvert.GetDictionaryKeyValueType() != null && typeToConvert.GetConstructor(Type.EmptyTypes) != null;

        }

​

        public override JsonConverter CreateConverter(Type typeToConvert, JsonSerializerOptions options)

        {

            var keyValueTypes = typeToConvert.GetDictionaryKeyValueType();

            var converterType = typeof(DictionaryAsArrayConverter<,,>).MakeGenericType(typeToConvert, keyValueTypes.Value.Key, keyValueTypes.Value.Value);

            return (JsonConverter)Activator.CreateInstance(converterType);

        }

    }

​

    public class DictionaryAsArrayConverter<TKey, TValue> : DictionaryAsArrayConverter<Dictionary<TKey, TValue>, TKey, TValue>

    {

    }

​

    public class DictionaryAsArrayConverter<TDictionary, TKey, TValue> : JsonConverter<TDictionary> where TDictionary : class, IDictionary<TKey, TValue>, new()

    {

        struct KeyValueDTO

        {

            public TKey Key { get; set; }

            public TValue Value { get; set; }

        }

        public override TDictionary Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)

        {

            var list = JsonSerializer.Deserialize<List<KeyValueDTO>>(ref reader, options);

            if (list == null)

                return null;

            var dictionary = typeToConvert == typeof(Dictionary<TKey, TValue>) ? (TDictionary)(object)new Dictionary<TKey, TValue>(list.Count) : new TDictionary();

            foreach (var pair in list)

                dictionary.Add(pair.Key, pair.Value);

            return dictionary;

        }

​

        public override void Write(Utf8JsonWriter writer, TDictionary value, JsonSerializerOptions options)

        {

            JsonSerializer.Serialize(writer, value.Select(p => new KeyValueDTO { Key = p.Key, Value = p.Value }), options);

        }

    }

    public static class TypeExtensions

    {

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

        {

            if (type == null)

                throw new ArgumentNullException();

            if (type.IsInterface)

                return new[] { type }.Concat(type.GetInterfaces());

            else

                return type.GetInterfaces();

        }

​

        public static KeyValuePair<Type, Type>? GetDictionaryKeyValueType(this Type type)

        {

            KeyValuePair<Type, Type>? types = null;

            foreach (var pair in type.GetDictionaryKeyValueTypes())

            {

                if (types == null)

                    types = pair;

                else

                    return null;

            }

            return types;

        }

        public static IEnumerable<KeyValuePair<Type, Type>> GetDictionaryKeyValueTypes(this Type type)

        {

            foreach (Type intType in type.GetInterfacesAndSelf())

            {

                if (intType.IsGenericType

                    && intType.GetGenericTypeDefinition() == typeof(IDictionary<,>))

                {

                    var args = intType.GetGenericArguments();

                    if (args.Length == 2)

                        yield return new KeyValuePair<Type, Type>(args[0], args[1]);

                }

            }

        }

    }

​

    public class ValueClass

    {

        public string Value { get; set; }

    }

​

    public class KeyValuePairDTO<TKey, TValue>

    {

        public TKey Key { get; set; }

        public TValue Value { get; set; }

    }

​

    public class MyDictionary : Dictionary<string, string> { }

​

    public class RootObject<T>

    {

        public T Dictionary { get; set; }

    }

​

    class TestClass

    {

        public static void Test()

        {

            var keys = new [] { "z", "a", "b", "c" };

            var intkeys = new [] { 5, 4, 3, 2, 1 };

            //Converter not working yet when property is declared as an interface

            //TestIDictionaryProperty();

            Test<Dictionary<string, string>, string, string>(keys.Select(s => (s, "value of s")));

            Test<SortedDictionary<string, string>, string, string>(keys.Select(s => (s, "value of s")));

            Test<Dictionary<string, ValueClass>, string, ValueClass>(keys.Select(s => (s, new ValueClass { Value = "value of s" })));

            Test<MyDictionary, string, string>(keys.Select(s => (s, "value of s")));

            Test<Dictionary<string, Dictionary<string, string>>, string, Dictionary<string, string>>(keys.Select(s => (s, keys.ToDictionary(k => k, k => "value of " + k))));

            Test<Dictionary<int, int>, int, int>(intkeys.Select(i => (i, i)));

        }   

        static void TestIDictionaryProperty()

        {

            var keys = new [] { "z", "a", "b", "c" };

            var root = new RootObject<IDictionary<string, string>>

            {

                Dictionary = keys.ToDictionary(s => s, s => "value of " + s),

            };

            var options = new JsonSerializerOptions

            {

                Converters = { new DictionaryConverterFactory() },

                PropertyNamingPolicy = JsonNamingPolicy.CamelCase,

                //WriteIndented = true,

            };

            var json = JsonSerializer.Serialize(root, options);

​

            var root2 = JsonSerializer.Deserialize<RootObject<IDictionary<string, string>>>(json, options);

            var json2 = JsonSerializer.Serialize(root2, options);

            var rootAsArray = JsonSerializer.Deserialize<RootObject<List<KeyValuePairDTO<string, string>>>>(json, options);

            Assert.IsTrue(root.Dictionary.Count == rootAsArray.Dictionary.Count);

            Assert.IsTrue(json == json2);

​

            Console.WriteLine("\nSerialized {0}:", root);

            Console.WriteLine(json);

        }

        static void Test<TDictionary, TKey, TValue>(IEnumerable<(TKey key, TValue value)> pairs) where TDictionary : class, IDictionary<TKey, TValue>, new()

        {

            var dictionary = new TDictionary();

            foreach (var pair in pairs)

                dictionary.Add(pair.key, pair.value);

​

            var options = new JsonSerializerOptions

            {

                Converters = { new DictionaryConverterFactory() },

                PropertyNamingPolicy = JsonNamingPolicy.CamelCase,

            };

​

            var json = JsonSerializer.Serialize(dictionary, options);

​

            var dictionary2 = JsonSerializer.Deserialize<TDictionary>(json, options);

​

            var json2 = JsonSerializer.Serialize(dictionary2, options);

​

            Assert.IsTrue(dictionary.Count == dictionary2.Count);

            var list = JsonSerializer.Deserialize<List<KeyValuePairDTO<TKey, TValue>>>(json, options);

​

            Assert.IsTrue(list.Count == dictionary2.Count);

            Assert.IsTrue(list.Select(i => i.Key).ToHashSet().SetEquals(dictionary.Keys));

            Assert.IsTrue(dictionary2.Keys.ToHashSet().SetEquals(dictionary.Keys));

            Console.WriteLine("\nSerialized {0}:", dictionary);

            Console.WriteLine(json);

​

        }

    }

​

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: {0} ({1})", System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription , GetNetCoreVersion());

            Console.WriteLine("Json.NET version: " + 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;

        }

    }

​