How to get simple product qty via configurable using Observer?

Question

I’m using the observer event called checkout_cart_product_add_after, but when I use this method below to get the quantity in stock I just can get the configurable product stock quantity, my simple product is working though.

$quoteItem = $observer->getEvent()->getQuoteItem();
$product = $quoteItem->getProduct();
$typeId = $product->getTypeId();

$productStockData = $product->getExtensionAttributes()->getStockItem(); 

$productQty = (int) $productStockData->getQty();

$message = __(
   '%1 may require a lead time.',
    $product->getName()
);
if ($product->getManageStock() && $productQty <= 0) {
    $this->messageManager->addWarningMessage($message);
}

Answer 1

First add the this in your construct:

public function __construct(
    ...
    \Magento\CatalogInventory\Api\StockRegistryInterface $stockRegistry
) {
    ...
    $this->_stockRegistry = $stockRegistry;
}

In my case, I created a method to use it:

public function getStockItem($productId){
    return $this->_stockRegistry->getStockItem($productId);
}

Then, you can use the method getCustomOption to get when it’s a configured product:

    $quoteItem = $observer->getEvent()->getQuoteItem();
    $product = $quoteItem->getProduct();
    $typeId = $product->getTypeId();

    if ($typeId == \Magento\ConfigurableProduct\Model\Product\Type\Configurable::TYPE_CODE) {
        $simpleProductSelected = $product->getCustomOption('simple_product')->getProductId();
        $productStockData = $this->getStockItem($simpleProductSelected);
    } else {
        $productStockData = $product->getExtensionAttributes()->getStockItem();
    }

    $productQty = (int) $productStockData->getQty();

    $message = __(
        '%1 may require a lead time.',
        $product->getName()
    );
    if ($this->stockMessaging->isEnable()) {
        $outOfStockQty = (int) $this->stockMessaging->getOutOfStockNumber($product);
        if ($productQty <= $outOfStockQty) {
            $this->messageManager->addWarningMessage($message);
        }
    } elseif ($product->getManageStock() && $productQty <= 0) {
        $this->messageManager->addWarningMessage($message);
    }