reference_field.py 文件源码

def validate(self, value):
        # avoiding circular reference
        from motorengine import Document

        if not isinstance(self.reference_type, type) or not issubclass(self.reference_type, Document):
            raise ValueError(
                "The field 'reference_document_type' argument must be a subclass of Document, not '%s'." % (
                    str(self.reference_type)
                )
            )

        if value is not None and not isinstance(value, (self.reference_type, ObjectId)):
            return False

        return value is None or isinstance(value, ObjectId) or (hasattr(value, '_id') and value._id is not None)