fields.py 文件源码

def validate(self, value):

        if not isinstance(value, (self.document_type, DBRef)):
            self.error('A ReferenceField only accepts DBRef or documents')

        if isinstance(value, Document) and value.id is None:
            self.error('You can only reference documents once they have been '
                       'saved to the database')

        if self.document_type._meta.get('abstract') and \
                not isinstance(value, self.document_type):
            self.error(
                '%s is not an instance of abstract reference type %s' % (
                    self.document_type._class_name)
            )