ASP.NET Core: validation attributes are ignored on fields defined in children types - asp.net-core

Question

My ASP.NET Core 2.1 API exposes the following input DTO in a POST endpoint:
[Route("test")]
[ApiController]
public class TestController : ControllerBase
{
[HttpPost("endpoint")]
public async Task<IActionResult> Post([Required]MyDTO dto)
{
// Some code
}
}
public class MyDTO
{
[JsonProperty("foo")]
[Required]
public Foo Foo { get; set; }
}
The Foo class is defined as follow:
[JsonConverter(typeof(FooConverter))]
public abstract class Foo
{
[JsonProperty("foo_type")]
[Required]
public string FooType { get; set; }
}
The FooConverter class is able to instantiate the right implementation based on the foo_type field:
public class FooConverter : JsonConverter<Foo>
{
public override bool CanRead => true;
public override bool CanWrite => false;
public override Foo ReadJson(JsonReader reader, Type objectType, Foo existingValue, bool hasExistingValue, JsonSerializer serializer)
{
var jObject = JObject.Load(reader);
Foo target = this.CreateFoo(jObject);
serializer.Populate(jObject.CreateReader(), target);
return target;
}
public override void WriteJson(JsonWriter writer, Foo value, JsonSerializer serializer)
{
throw new NotImplementedException();
}
private Foo CreateFoo(JObject jObject)
{
string fooType = jObject.Value<string>("foo_type");
switch (fooType)
{
case "foo1":
return new Foo1();
case "foo2":
return new Foo2();
default:
throw new JsonSerializationException($"Invalid 'foo_type' '{fooType}'");
}
}
}
Here is one of the implementations of the Foo abstract class:
public class Foo1 : Foo
{
[JsonProperty("bar")]
[Required]
public string Bar { get; set; }
}
My problem is that the [Required] attribute on Foo1.Bar is ignored by ASP.NET validation, even though the [Required] attribute on Foo.FooType works as expected. How can I automatically validate the fields defined in the implementation types so that it works the same as with other fields?

Answer 1

Replace:
var jObject = JObject.Load(reader);
with:
JToken jObject = JToken.ReadFrom(reader);