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 Microsoft.VisualStudio.TestTools.UnitTesting;

​

using Debug = System.Console;

​

//System.Text.Json: JsonExtensionData deserialization silently fails for a get-only, preallocated dictionary property.

​

    public class Model

    {

        readonly Dictionary<string, object> extensionData = new Dictionary<string, object>();

​

        [JsonExtensionData]

        public Dictionary<string, object> ExtensionData { get => extensionData; set => throw new NotImplementedException(); }

    }

​

    public class TestClass

    {

        [TestMethod]

        public void TestReadOnlyExtensionDataProperty()

        {

            var model1 = new Model { ExtensionData = { { "item", "item value" } } };

​

            var json = JsonSerializer.Serialize(model1);

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            Debug.WriteLine(json); // Prints {"item":"item value"} as expected

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            Assert.AreEqual(json, "{\"item\":\"item value\"}"); // Passes.

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            var model2 = JsonSerializer.Deserialize<Model>(json);

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            Assert.AreEqual(model1.ExtensionData.Count, model2.ExtensionData.Count, "model2.ExtensionData.Count"); // Passes!

        }

    }

​

    public class Program

    {

        public static void Main()

        {

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

            Console.WriteLine(string.Format("{0} version: {1}", typeof(JsonSerializer).Namespace, typeof(JsonSerializer).Assembly.FullName));

            Console.WriteLine();

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            try

            {

                new TestClass().TestReadOnlyExtensionDataProperty();

            }

            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;

        }

    }

​