Django REST Framework: raise error when extra fields are present on POST

Came across this question and found that using object level validation is a bit easier. This entails simply defining a validate method:

class ModelASerializer(serializers.ModelSerializer):
    ...
    def validate(self, data):
        if hasattr(self, 'initial_data'):
            unknown_keys = set(self.initial_data.keys()) - set(self.fields.keys())
            if unknown_keys:
                raise ValidationError("Got unknown fields: {}".format(unknown_keys))
        return data