Could it be possible to throw an exception flag if a user tried to add products that are not in the same category as the items already in their cart? Much the same way that Magento throws a flag if a user tries to add both a Nominal and Regular product to the same cart.

1 Answer 1


I have written the sample code, this link is the actual answer that will work for you:

Create an observer for event checkout_cart_product_add_after




class MagePal_LimitCartProductByCategory_Model_Observer 

    public function cartlimit(Varien_Event_Observer  $observer)
        $category_ids = array();

        $quote = Mage::getSingleton('checkout/session')->getQuote();
        foreach($quote->getAllVisibleItems() as $item){
              $product = Mage::getModel('catalog/product')->load($item->getId());
              $product_category_ids = explode(",", $product->getCategoryIds());
              //$product_category_ids = $product->getCategoryIds();

              array_push($category_ids, $product_category_ids);

        $justAdded = $observer->getQuoteItem();

        $productJustAdded = Mage::getModel('catalog/product')->load($justAdded->getId());

        //total the category id in $category_ids
        //if $productJustAdded->getCategoryIds exist in $category_ids, 
        //then check to see if category id count greater than 3
        // if true then add error msg and try setting the qty to 0

        return $this;
  • Is this complete code? I tried and its not working
    – Indian
    Commented Oct 12, 2017 at 11:31

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