(Photo: Speed Limit 14 MPH by bredgur)

Sometimes the client will ask that the quantity of items you can add to the cart be limited to some number, say 14 like in the photo above. 🙂

Often people will implement this by putting in checks throughout the JSP.  But this is not the best solution because it is more labor intensive and you may miss something.

Another solution is to deal with the issue in the CartModifierFormHandler by extending the doAddItemsToOrder method.  Simply check the quantity of each AddCommerceItemInfo item and make sure that its quantity plus the quantity of the same item already in the cart does not go over the limit.  If it does modify the quantity in the AddCommerceItemInfo item appropriately.

Here is how I implemented this.

    @Override
    protected void doAddItemsToOrder(DynamoHttpServletRequest pRequest,
            DynamoHttpServletResponse pResponse) throws ServletException,
            IOException {

        // fetch the order
        Order order = getOrder();
        if (order == null) {
            String msg = formatUserMessage(MSG_NO_ORDER_TO_MODIFY, pRequest,
                    pResponse);
            throw new ServletException(msg);
        }

        // iterate through the add commerce item infos, making sure that adding
        // any of them will not result in a quantity greater than LIMIT
        AddCommerceItemInfo[] addCommerceItemInfos = getItems();
        for (int ii = 0; ii < addCommerceItemInfos.length; ii++) {

            // see if there is a commerce item already in the order for the next
            // add commerce item info
            AddCommerceItemInfo addCommerceItemInfo = addCommerceItemInfos[ii];
            String catalogRefId = addCommerceItemInfo.getCatalogRefId();
            CommerceItem commerceItem = findCommerceItemByCatalogRefId(order,
                    catalogRefId);
            if (commerceItem == null) {
                continue;
            }

            // check that the quantity we add won't result in a total quantity
            // greater than LIMIT
            long addQty = addCommerceItemInfo.getQuantity();
            long qty = commerceItem.getQuantity();
            if (qty >= LIMIT) {
                addCommerceItemInfo.setQuantity(0);
            } else if (qty + addQty > LIMIT) {
                long newAddQty = LIMIT - qty;
                addCommerceItemInfo.setQuantity(newAddQty);
            }
        }

        super.doAddItemsToOrder(pRequest, pResponse);
    }

    protected CommerceItem findCommerceItemByCatalogRefId(Order pOrder,
            String pCatalogRefId) {
        for (int ii = 0; ii < numCommerceItems; ii++) {
            CommerceItem commerceItem = (CommerceItem) commerceItems.get(ii);
            String catalogRefId = commerceItem.getCatalogRefId();
            if (catalogRefId.equals(pCatalogRefId))
                return commerceItem;
        }
        return null;
    }