protected function prepareExpression(DataControllerCallContext $callcontext, AbstractRequest $request, $datasetName, $columnName, $columnDataType) {
        $proxy = new DateTimeProxy();

        $dt = new DateTime();
        $dt->setDate(
            $proxy->getYear(),
            DateTimeProxy::getFirstMonthOfQuarter($proxy->getQuarter()),
            1);

        return $this->prepareExpressionImpl($callcontext, $request, $datasetName, $columnName, $columnDataType, $this->formatDate($dt));
    }