def getall(self):
        try:
            spec = {'data': {'$exists': 1}}
            fields = {'_id': 0}
            sort = [('tid', 1)]
            cur = self.db.docs.find(spec, fields, sort=sort)
        except Exception as e:
            raise DatabaseException(e)
        return [Document(**row) for row in cur]
def __init__(self, root, transforms=None):

        super().__init__(root=root)
        self.transforms = transforms

        self._flow_list = []
        self._image_list = []