protected function addChange($calendarId, $objectUri, $operation)
    {
        $stmt = $this->pdo->prepare('INSERT INTO '.$this->calendarChangesTableName.' (uri, synctoken, calendarid, operation) SELECT ?, synctoken, ?, ? FROM '.$this->calendarTableName.' WHERE id = ?');
        $stmt->execute([
            $objectUri,
            $calendarId,
            $operation,
            $calendarId,
        ]);
        $stmt = $this->pdo->prepare('UPDATE '.$this->calendarTableName.' SET synctoken = synctoken + 1 WHERE id = ?');
        $stmt->execute([
            $calendarId,
        ]);
    }