Doctrine\ORM\EntityManager::transactional PHP Method

    public function transactional(Closure $func)
    {
        $this->conn->beginTransaction();
        try {
            $func($this);
            $this->flush();
            $this->conn->commit();
        } catch (Exception $e) {
            $this->close();
            $this->conn->rollback();
            throw $e;
        }
    }

 /**
  * @param float $discount
  */
 public function apply($discount)
 {
     $this->entityManager->transactional(function () use($discount) {
         foreach ($this->items->findAll() as $item) {
             $item->applyDiscount($discount);
         }
     });
     $this->entityManager->clear();
 }