lock product qty increase while adding to cart

Question

I found a problem using a custom "gift" extension for magento. It let the user choose a gift product in the checkout cart page. So the user will find under the cart a product grid and can select max 1 product to get as gift and then add it to cart.

My problem is that after the user add product he's still able to edit the qty. So he can order 10 items of product as gift.

I need to force user to don't edit the product quantity for the "gift" products in cart.

The products listed as "Gifts" can be also purchased as regular products so that rule has to be applied on the "Gift" situation.

Actually the function "add cart" of the extension is this one:

public function addAction()
{   
    if ($this->getRequest()->isGet()) {
        $gift_id = $this->getRequest()->getParam('gift', 0);
        if($gift_id){
            if(!Mage::helper('gifts')->isGiftUsed() && in_array($gift_id, Mage::helper('gifts')->getGiftsIds())){
                $quote = Mage::getSingleton('checkout/session')->getQuote();
                $cart = Mage::getModel('checkout/cart');
                $product = new Mage_Catalog_Model_Product();
                $product->load($gift_id);

                $cart->addProduct($product, 1);
                $cart->save();

                foreach ($quote->getAllItems() as $item) {

                    if ($item->getProductId() == $gift_id) {
                        $item->setCustomPrice(0);
                        $item->setOriginalCustomPrice(0);
                        //$item->setOption('inventory_max_sale_qty',1);
                    }
                }

                $cart->init();
                $cart->save();          

                Mage::getSingleton('checkout/session')->setCartWasUpdated(true);
            }
        }
    }
    $this->_redirect('checkout/cart');
}

thank you

Answer 1

Try editing the product that is the gift.

On the 'Inventory' tab check the 'Maximum Qty Allowed in Shopping Cart' value. Try setting this value to '1' for the gift product.

UPDATE:

To only restrict the quantity if it is a gift:

if ($item->getProductId() == $gift_id) {
    $item->setMaxSaleQty(1);
    $item->setCustomPrice(0);
    $item->setOriginalCustomPrice(0);
}

UPDATE It occurred to me you may also need to modify the setUseConfigMaxSaleQty parameter like this (although I haven't tested so I'm not sure):

$item->setUseConfigMaxSaleQty(1);
$item->setMaxSaleQty(1);