How to get product Notify Qty by product id in magento 2?

Question

$productId = $orderItem->getProductId();

Answer 1

Would something like this work? This should return the notify stock quantity value for the first stock item found for a given product ID.

/**
 * @param StockItemCriteriaInterfaceFactory $stockItemCriteriaFactory
 * @param StockItemRepositoryInterface $stockItemRepository
 */
public function __construct(
    \Magento\CatalogInventory\Api\StockItemCriteriaInterfaceFactory $stockItemCriteriaFactory,
    \Magento\CatalogInventory\Api\StockItemRepositoryInterface $stockItemRepository
) {
    $this->stockItemCriteriaFactory = $stockItemCriteriaFactory;
    $this->stockItemRepository = $stockItemRepository;
}

/**
 * @param int $productId
 * @return float|null
 */
public function getNotifyStockQtyFromProductId(int $productId): ?float
{
    $criteria = $this->stockItemCriteriaFactory->create();
    $criteria->setProductsFilter($productId);
    $stockItemCollection = $this->stockItemRepository->getList($criteria);
    $stockItems = $stockItemCollection->getItems();

    if (empty($stockItems)) {
        // No stock item found for product.
        return null;
    }

    /** @var \Magento\CatalogInventory\Api\Data\StockItemInterface $stockItem */
    $stockItem = reset($stockItems);
    return $stockItem->getNotifyStockQty();
}

Answer 2

May be you should know little: Low stock notification alert the merchant that the salable quantity of a stock has reached a critical threshold.

The Notify Quantity fields (Catalog > Products > specific product > Assigned Sources section) override all other settings. The merchant can assign a different threshold for each source for the specific product.

So, the Notify Qty is the API interface method StockConfiguration.php Model as:

$this->stockConfiguration->getNotifyStockQty($this->getStoreId());