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 pop(self, key, default=None):
        value = self._collection.pop(key, default)
        return self._to_python(value)