def insert(self, doc, synced=False):
        doc.id = self.get_next_id()
        doc.synced = synced
        try:
            self.db.docs.insert(doc)
        except Exception as e:
            raise DatabaseException(e)
        return doc
def __init__(self, root, transforms=None):

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

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