Eccube\Service\CartService::downProductQuantity PHP 메소드

    public function downProductQuantity($productClassId)
    {
        $quantity = $this->getProductQuantity($productClassId) - 1;
        if ($quantity > 0) {
            $this->setProductQuantity($productClassId, $quantity);
        } else {
            $this->removeProduct($productClassId);
        }
        return $this;
    }