Magento 2: Observer add product to cart?

Question

I've read some other post about adding products to cart, but nothing seems to fit.

I've an observer for checkout_cart_update_items_before that adds another product in same qty if specific product is added.

So quantity for product A and B should always be same.

Observer:

public function execute(Observer $observer): void
{
    /** @var \Magento\Framework\DataObject $info */
    $info = $observer->getInfo();
    /* @var \Magento\Quote\Model\Quote $quote */
    $quote = $observer->getCart()->getQuote();
    $cartItems = $quote->getAllItems();

    $update = false;
    $newQty = 0;

    foreach ($cartItems as $item) {
        if ($this->helper->isDepositProduct($item->getProduct())) {
            $newQty += $info[$item->getId()]['qty'];
            $item->setQty($info[$item->getId()]['qty']);
            $update = true;
        }
    }

    if ($update) {
        $addItem = $this->helper->getDepositProduct();
        if ($addItem && $addItem->getId()) {
            $addQuoteItem = $quote->getItemByProduct($addItem);
            if ($addQuoteItem) {
                if ($newQty <= 0) {
                    $quote->removeItem($addQuoteItem->getId());
                    $quote->save();
                } else {
                    $addQuoteItem->setQty($newQty);
                    $observer->getCart()->save();
                }
            }
        }
    }
}

Works:

Luma theme ... update from mini-cart popup works.

Doesn't Works:

• update quantity in cart
• update quantity in "product options" edit (pen icon in cart/popup)

It only updates qty count next to cart icon in header, but totals and qty input fields do not get changed on the cart page.

This code was ported from M1 and worked there w/o problems :(. So, what is the difference between updating via mini-cart-popup and in checkout cart?

Is there any problems with $observer->getCart()->save();?

Answer 1

If I remember correct, that observer event gets quote before it is saved. So you taking quote, that is not yet saved in database (if added +1 quantity, it wont be in that observer quote). Saving quote is done after that event. So I think it is not good for you in general, because you will miss real quantity. I suggest to use plugin for it. Also, for adding product to quote you can use event checkout_cart_add_product_complete. There will be info about added product, so you know what was added and do what you need. For updating quantity I suggest to write plugin for execute function maybe vendor/magento/module-checkout/Controller/Cart/UpdatePost.php. Updating is done in in function _updateShoppingCart(), but it is protected, so you cannot write plugin. If you want you can even rewrite it, your choice. Just do your stuff after $this->cart->updateItems($cartData)->save();. This way you won't do some save before magento did its own stuff and wont ruin quote data and totals.