def validate_fields_only(self, val):
        """
        To pass field validation, no required field should be missing.

        This method assumes that the contents of each field have already been
        validated on assignment, so it's merely a presence check.

        FIXME(kelkabany): Since the definition object does not maintain a list
        of which fields are required, all fields are scanned.
        """
        for field_name in self.definition._all_field_names_:
            if not hasattr(val, field_name):
                raise ValidationError("missing required field '%s'" %
                                      field_name)
To pass field validation, no required field should be missing.

        This method assumes that the contents of each field have already been
        validated on assignment, so it's merely a presence check.

        FIXME(kelkabany): Since the definition object does not maintain a list
        of which fields are required, all fields are scanned.