[cloud_firestore_odm] Should firestoreJsonConverters allow fields to be json encodable?

[enricava]

I am having a lot of trouble with firestoreJsonConverters and DateTimes.

I want to serialize a model which uses a DateTime to json and then encode it. I am currently using this model with the firestore ODM and it works fine. It can be simplified to the followingFoo class:

@JsonSerializable(
  createFieldMap: true,
  createToJson: true,
  explicitToJson: true,
  converters: firestoreJsonConverters,
)
class Foo {
  const Foo({required this.date});

  final DateTime date;

  factory Foo.fromJson(Map<String, Object?> json) =>
      _$FooFromJson(json);

  Map<String, Object?> toJson() => _$FooToJson(this);
}

Now, I would like to also allow this model to be used outside of firestore and be encoded to a String:

test('encode to json', () {
  final foo = Foo(date: DateTime.now());
  jsonEncode(foo.toJson()); // <- this line throws
});

The error: Converting object to an encodable object failed: Instance of 'Timestamp'.

What exactly is going on here? If I force Foo.date to use FirestoreTimestampConverter, this test will not throw but the ODM will fail to decode Foo, with the error: Instance of 'Timestamp': type 'Timestamp' is not a subtype of type 'String' at dart:sdk_internal 3747:11

If, however, Foo is set to use FirestoreDatetimeConverter I get the previous issue.

Any help is much appreciated, I am a bit puzzled as to how to fix this, and have not found issues about this. Can I not use the same model for both firestore ODM and json encoding?