ASP.Net Core 2.2 - separate serializer settings for input and output

Question

ASP.Net Core 2.2 allows to set serializer settings using MvcJsonOptions.SerializerSettings property. The problem is that it affects both input and output. Is there a way to have separate options for input (deserialization) and output (serialization)? In particular, I need to set a different behavior for NullValueHandling settings: ignore null errors for non-nullable fields when deserializing client json but keep nulls for defined model fields when serializing the result.

For example, I have a C# model for request:

public class SomeEntity
{
    public int Id { get; set; }
    public int? ParentId { get; set; }
    public string Name { get; set; }
}

And input JSON: { id: null, parentId: null, name: "test" }. The deserialization fails for NullValueHandling.Include but works for NullValueHandling.Ignore.

But when I serialize an entity like this one

new SomeEntity
{
    Id = 1,
    ParentId = null,
    Name = "test"
}

It keeps null with NullValueHandling.Include: { id: 1, parentId: null, name: "test" } but erases it with NullValueHandling.Ignore: { id: 1, name: "test" }.

I need to achieve the "Ignore" scenario for input and "Include" for output.

Answer 1

Finally found this workaround: https://github.com/aspnet/Mvc/issues/4562#issuecomment-226100352

public class CustomSerializerSettingsSetup : IConfigureOptions<MvcOptions>
{
    private readonly ILoggerFactory _loggerFactory;
    private readonly ArrayPool<char> _charPool;
    private readonly ObjectPoolProvider _objectPoolProvider;

    public CustomSerializerSettingsSetup(
        ILoggerFactory loggerFactory,
        ArrayPool<char> charPool,
        ObjectPoolProvider objectPoolProvider)
    {
        _loggerFactory = loggerFactory;
        _charPool = charPool;
        _objectPoolProvider = objectPoolProvider;
    }

    public void Configure(MvcOptions options)
    {
        options.OutputFormatters.RemoveType<JsonOutputFormatter>();
        options.InputFormatters.RemoveType<JsonInputFormatter>();
        options.InputFormatters.RemoveType<JsonPatchInputFormatter>();

        var outputSettings = new JsonSerializerSettings();
        options.OutputFormatters.Add(new JsonOutputFormatter(outputSettings, _charPool));

        var inputSettings = new JsonSerializerSettings();
        var jsonInputLogger = _loggerFactory.CreateLogger<JsonInputFormatter>();
        options.InputFormatters.Add(new JsonInputFormatter(
            jsonInputLogger,
            inputSettings,
            _charPool,
            _objectPoolProvider));

        var jsonInputPatchLogger = _loggerFactory.CreateLogger<JsonPatchInputFormatter>();
        options.InputFormatters.Add(new JsonPatchInputFormatter(
            jsonInputPatchLogger,
            inputSettings,
            _charPool,
            _objectPoolProvider));
    }
}

and

services.TryAddEnumerable(
    ServiceDescriptor.Transient<IConfigureOptions<MvcOptions>, CustomSerializerSettingsSetup>());

in service provider configuration