Magento 2 : How to get parent method while we extend the class

Question

I am extending this class : Magento\Sales\Model\Service\InvoiceService

My extended file :

namespace Company\Vendor\Model\Service;

use Magento\Sales\Api\InvoiceManagementInterface;
use Magento\Sales\Model\Order;

class InvoiceService extends \Magento\Sales\Model\Service\InvoiceService implements InvoiceManagementInterface
{

    public function prepareInvoice(Order $order, array $qtys = [])
    {
        $invoice = $this->orderConverter->toInvoice($order);
        $totalQty = 0;
        $qtys = parent::prepareItemsQty($order, $qtys); // modified line
        //$qtys = $this->prepareItemsQty($order, $qtys); // core line
        foreach ($order->getAllItems() as $orderItem) {
            if (!$this->_canInvoiceItem($orderItem)) {
                continue;
            }
            $item = $this->orderConverter->itemToInvoiceItem($orderItem);
            if ($orderItem->isDummy()) {
                $qty = $orderItem->getQtyOrdered() ? $orderItem->getQtyOrdered() : 1;
            } elseif (isset($qtys[$orderItem->getId()])) {
                $qty = (double) $qtys[$orderItem->getId()];
            } elseif (empty($qtys)) {
                $qty = $orderItem->getQtyToInvoice();
            } else {
                $qty = 0;
            }
            $totalQty += $qty;
            $this->setInvoiceItemQuantity($item, $qty);
            $invoice->addItem($item);
        }
        $invoice->setTotalQty($totalQty);
        $invoice->collectTotals();
        $order->getInvoiceCollection()->addItem($invoice);
        return $invoice;
    }
}

I am getting an error here:$this->prepareItemsQty($order, $qtys);

So I am a bit confused about how to call another function of parent functions here.

Note: I don't want to declare code of prepareItemsQty() here (extended class).

Answer 1

Function prepareItemsQty(Order $order, array $qtys = []) is declared as private in the parent class, so you can't access it directly from subclasses. You can declare the private method as protected instead but I not recommend do it with Magento Core files. Or you can use the following code:

public function prepareInvoice(Order $order, array $qtys = [])
{
    $invoice = parent::prepareInvoice($order, $array);

    // To do something

    return $invoice;
}