Eccube\Service\CsvExportService::exportData PHP Method

    public function exportData(\Closure $closure)
    {
        if (is_null($this->qb) || is_null($this->em)) {
            throw new \LogicException('query builder not set.');
        }
        $this->fopen();
        $query = $this->qb->getQuery();
        foreach ($query->getResult() as $iteratableResult) {
            $closure($iteratableResult, $this);
            $this->em->detach($iteratableResult);
            $query->free();
            flush();
        }
        $this->fclose();
    }