New JSON serializer -> inheritance

[ErazerBrecht]

Describe the bug

Probably it's a feature. And probably this is a question that belongs @ stackoverflow.
But I couldn't find anything.

When using AspNet Core 3.0 and not adding AddNewtonsoftJson (aka using the new JSON serializer) it 'ignores' inheritance

To Reproduce

https://github.com/ErazerBrecht/JsonTest

Most important file: https://github.com/ErazerBrecht/JsonTest/blob/master/JsonTest/Controllers/ValueController.cs

By adding 'AddNewtonsoftJson' in the Startup.cs I get my 'excepted behavior'.

Actual behaviour:

{
    transportations: [
    {
        speed: 120
    },
    {
        speed: 90
    }]
}

Expected behavior

{
    transportations: [
    {
         horsePower: 130,
         speed: 120
    },
    {
        humanCapacity: 50,
        speed: 90
    }]
}

Additional context

I checked https://docs.microsoft.com/en-us/dotnet/api/system.text.json.jsonserializeroptions?view=netcore-3.0. But I couldn't find a setting related to 'inheritance'.
So if it's not a bug, is there somewhere documention on how to fallback to what JSON.NET used to do?

Thanks for your time
Sincerely, Brecht

[pranavkm]

You're likely running in to https://github.com/dotnet/corefx/issues/38650. Support for polymorphism isn't part of the 3.0 release. If you require it, I'd recommend continuing to use Newtonsoft.Json. Feel free to use the linked issue for further discussions or questions.

[ErazerBrecht]

Thx I'll subscribe to that issue 👍