//https://stackoverflow.com/questions/65402006/how-can-i-correctly-skip-an-unknown-property-inside-the-jsonconvertert-read

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

​

// How can I correctly skip an unknown property inside JsonConverter<T>.Read()?

​

    // Example taken from https://docs.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-converters-how-to?pivots=dotnet-5-0#support-polymorphic-deserialization

​

    public class Person

    {

        public string Name { get; set; }

    }

​

    public class Customer : Person

    {

        public decimal CreditLimit { get; set; }

    }

​

    public class Employee : Person

    {

        public string OfficeNumber { get; set; }

    }

​

    public class PersonConverterWithTypeDiscriminator : JsonConverter<Person>

    {

        enum TypeDiscriminator

        {

            Customer = 1,

            Employee = 2

        }

​

        public override bool CanConvert(Type typeToConvert) =>

            typeof(Person).IsAssignableFrom(typeToConvert);

​

        public override Person Read(

            ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)

        {

            if (reader.TokenType != JsonTokenType.StartObject)

            {

                throw new JsonException();

            }

​

            reader.Read();

            if (reader.TokenType != JsonTokenType.PropertyName)

            {

                throw new JsonException();

            }

​

            string propertyName = reader.GetString();

            if (propertyName != "TypeDiscriminator")

            {

                throw new JsonException();

            }

​

            reader.Read();

            if (reader.TokenType != JsonTokenType.Number)

            {

                throw new JsonException();

            }

​

            TypeDiscriminator typeDiscriminator = (TypeDiscriminator)reader.GetInt32();

            Person person = typeDiscriminator switch

            {

                TypeDiscriminator.Customer => new Customer(),

                TypeDiscriminator.Employee => new Employee(),

                _ => throw new JsonException()

            };

​

            while (reader.Read())

            {

                if (reader.TokenType == JsonTokenType.EndObject)

                    return person;

                else if (reader.TokenType != JsonTokenType.PropertyName)

                    throw new JsonException();

​

                propertyName = reader.GetString();

                reader.Read();

                switch (propertyName)

                {

                    case "CreditLimit":

                        decimal creditLimit = reader.GetDecimal();

                        ((Customer)person).CreditLimit = creditLimit;

                        break;

                    case "OfficeNumber":

                        string officeNumber = reader.GetString();

                        ((Employee)person).OfficeNumber = officeNumber;

                        break;

                    case "Name":

                        string name = reader.GetString();

                        person.Name = name;

                        break;

                    default:

                        reader.Skip();

                        break;

                }

            }

​

            throw new JsonException();

        }

​

        public override void Write(

            Utf8JsonWriter writer, Person person, JsonSerializerOptions options)

        {

            writer.WriteStartObject();

​

            if (person is Customer customer)

            {

                writer.WriteNumber("TypeDiscriminator", (int)TypeDiscriminator.Customer);

                writer.WriteNumber("CreditLimit", customer.CreditLimit);

            }

            else if (person is Employee employee)

            {

                writer.WriteNumber("TypeDiscriminator", (int)TypeDiscriminator.Employee);

                writer.WriteString("OfficeNumber", employee.OfficeNumber);

            }

​

            writer.WriteString("Name", person.Name);

​

            writer.WriteEndObject();

        }

    }

​

    class TestClass

    {

        public static void Test()

        {

            var options = new JsonSerializerOptions

            {

                Converters = { new PersonConverterWithTypeDiscriminator() },

            };

            var json = @"{""TypeDiscriminator"":2,""OfficeNumber"":""1-111-111-1111"",""Name"":""my name"", ""ExtraData"" : {""Value"" : ""extra value""} }";

            Console.WriteLine(json);

            var person = JsonSerializer.Deserialize<Person>(json, options);

            person.Dump();

        }   

    }

​

    public class Program

    {

        public static void Main()

        {

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

            Console.WriteLine("System.Text.Json 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.Location.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;

        }

    }

​