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I need to detect whenever the inventory level of a product changes. I've had some success using the cataloginventory_stock_item_save_after event which is triggered when inventory is changed in the backend, or when an order is cancelled on the frontend (via Paypal), but is not triggered when a product is purchased from the frontend.

I'm hooking into the cataloginventory_stock_item_save_after event like this:

<global> <events> <cataloginventory_stock_item_save_after> <observers> <cataloginventory_stock_item_save_after_handler> <type>model</type> <class>stockchange/observer</class> <method>stockChange</method> </cataloginventory_stock_item_save_after_handler> </observers> </cataloginventory_stock_item_save_after> </events> 

<?php class FashionBunker_StockChange_Model_Observer { public function stockChange(Varien_Event_Observer $observer) {

Do I need to use another event to capture the inventory change when a customer purchases something, or is there something wrong with the way I've hooked into the event?

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2 Answers 2

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28

It has been some time ago that I build something for this, I had to listen to multiple observers because they where not all handled by the save of the cataloginventory, I have to following code:

 <events> <cataloginventory_stock_item_save_commit_after> <observers> <genmato_stockupdate> <class>genmato_stockupdate/observer</class> <method>catalogInventorySave</method> </genmato_stockupdate> </observers> </cataloginventory_stock_item_save_commit_after> <sales_model_service_quote_submit_before> <observers> <genmato_stockupdate> <class>genmato_stockupdate/observer</class> <method>subtractQuoteInventory</method> </genmato_stockupdate> </observers> </sales_model_service_quote_submit_before> <sales_model_service_quote_submit_failure> <observers> <genmato_stockupdate> <class>genmato_stockupdate/observer</class> <method>revertQuoteInventory</method> </genmato_stockupdate> </observers> </sales_model_service_quote_submit_failure> <sales_order_item_cancel> <observers> <genmato_stockupdate> <class>genmato_stockupdate/observer</class> <method>cancelOrderItem</method> </genmato_stockupdate> </observers> </sales_order_item_cancel> <sales_order_creditmemo_save_after> <observers> <genmato_stockupdate> <class>genmato_stockupdate/observer</class> <method>refundOrderInventory</method> </genmato_stockupdate> </observers> </sales_order_creditmemo_save_after> </events>

And in the observer the following code:

public function catalogInventorySave(Varien_Event_Observer $observer) { if ($this->isEnabled()) { $event = $observer->getEvent(); $_item = $event->getItem(); if ((int)$_item->getData('qty') != (int)$_item->getOrigData('qty')) { $params = array(); $params['product_id'] = $_item->getProductId(); $params['qty'] = $_item->getQty(); $params['qty_change'] = $_item->getQty() - $_item->getOrigData('qty'); } } } public function subtractQuoteInventory(Varien_Event_Observer $observer) { if ($this->isEnabled()) { $quote = $observer->getEvent()->getQuote(); foreach ($quote->getAllItems() as $item) { $params = array(); $params['product_id'] = $item->getProductId(); $params['sku'] = $item->getSku(); $params['qty'] = $item->getProduct()->getStockItem()->getQty(); $params['qty_change'] = ($item->getTotalQty() * -1); } } } public function revertQuoteInventory(Varien_Event_Observer $observer) { if ($this->isEnabled()) { $quote = $observer->getEvent()->getQuote(); foreach ($quote->getAllItems() as $item) { $params = array(); $params['product_id'] = $item->getProductId(); $params['sku'] = $item->getSku(); $params['qty'] = $item->getProduct()->getStockItem()->getQty(); $params['qty_change'] = ($item->getTotalQty()); } } } public function cancelOrderItem(Varien_Event_Observer $observer) { if ($this->isEnabled()) { $item = $observer->getEvent()->getItem(); $qty = $item->getQtyOrdered() - max($item->getQtyShipped(), $item->getQtyInvoiced()) - $item->getQtyCanceled(); $params = array(); $params['product_id'] = $item->getProductId(); $params['sku'] = $item->getSku(); $params['qty'] = $item->getProduct()->getStockItem()->getQty(); $params['qty_change'] = $qty; } } public function refundOrderInventory(Varien_Event_Observer $observer) { if ($this->isEnabled()) { $creditmemo = $observer->getEvent()->getCreditmemo(); foreach ($creditmemo->getAllItems() as $item) { $params = array(); $params['product_id'] = $item->getProductId(); $params['sku'] = $item->getSku(); $params['qty'] = $item->getProduct()->getStockItem()->getQty(); $params['qty_change'] = ($item->getQty()); } } }

Hope this is a bit what you are looking for.

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  • When I used this as is, it produced a 500 server error when canceling orders and placing orders didn't work. I had to delete the if ($this->isEnabled()) condition from the functions for this to work. Any reason why this is the case? Is it because I'm using the singleton type? Thanks Commented Sep 6, 2017 at 23:28
  • @MoustafaElqabbany its a method you would have to implement, just remove the clause from the methods and the If-Brackets and you're fine. Commented Jul 16, 2020 at 9:38
5

You cannot use any event related to the stock item model, because Magento uses an optimized SQL query to decrease stock for all ordered items at once, bypassing the model.

I solved this with a rewrite of Mage_CatalogInventory_Model_Stock where I added an additional event:

<?php /** * Add events to observe stock qty change * * @author Fabian Schmengler * */ class SGH_ShippingExpress_Model_CatalogInventory_Stock extends Mage_CatalogInventory_Model_Stock { const EVENT_CORRECT_STOCK_ITEMS_QTY_BEFORE = 'cataloginventory_stock_item_correct_qty_before'; const EVENT_CORRECT_STOCK_ITEMS_QTY_AFTER = 'cataloginventory_stock_item_correct_qty_after'; /** * (non-PHPdoc) * @see Mage_CatalogInventory_Model_Stock::registerProductsSale() */ public function registerProductsSale($items) { Mage::dispatchEvent(self::EVENT_CORRECT_STOCK_ITEMS_QTY_BEFORE, array( 'stock' => $this, 'items_obj' => (object)array('items' => &$items), 'operator' => '-' )); $result = parent::registerProductsSale($items); Mage::dispatchEvent(self::EVENT_CORRECT_STOCK_ITEMS_QTY_AFTER, array( 'stock' => $this, 'items' => $items, 'fullsave_items' => $result, 'operator' => '-' )); return $result; } /** * (non-PHPdoc) * @see Mage_CatalogInventory_Model_Stock::revertProductsSale() */ public function revertProductsSale($items) { Mage::dispatchEvent(self::EVENT_CORRECT_STOCK_ITEMS_QTY_BEFORE, array( 'stock' => $this, 'items_obj' => (object)array('items' => &$items), 'operator' => '+' )); $result = parent::revertProductsSale($items); Mage::dispatchEvent(self::EVENT_CORRECT_STOCK_ITEMS_QTY_AFTER, array( 'stock' => $this, 'items' => $items, 'fullsave_items' => $result, 'operator' => '+' )); return $result; } }

Then the observer for cataloginventory_stock_item_correct_qty_after can look like this:

 /** * @var $items array array($productId => array('qty'=>$qty, 'item'=>$stockItem)) */ $items = $observer->getItems(); foreach ($items as $productId => $item) { $stockItem = $item['item']; $product = $stockItem->getProduct(); // Do anything you need with $stockItem and $product here }

I recommend not to do heavy processing or additional database calls (which are necessary to detect if the product is out of stock for example), but to add the products to a queue that is processed by a cronjob, to minimize additional load time for the user.

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  • $stockItem->canSubtractQty() is not working in the observer nor is $stockItem->getId().. any tips? Seems I cannot access the methods Commented Aug 23, 2016 at 19:23
  • Fabian, what is the purpose of adding custom events here as you can add the feature with the overwritten function itself? is this only to decouple? Please guide. Commented Dec 23, 2017 at 10:31
  • @MagentoLearner yes, it made it easier for me to reuse and add different features. Technically you could also introduce a private method instead Commented Dec 23, 2017 at 17:48
  • This may involve rewriting a core class, but it's still the most complete solution here. Sometimes you just have to add your own events on M1 :P Commented Sep 13, 2018 at 14:42

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