Cheltenham Web Design and Drupal Development | Tigerfish Interactive

Recently we created a Drupal 6 store using Ubercart 2, but we just wanted users to be able to purchase one item at a time. This posed an interesting, but not insurmountable, problem.

The main issue here is that by default, the user may visit his or her shopping cart and choose any quantity of items. In order to restrict the user to force him or her to just buy one, we had a few options:

• Hide the shopping cart but this is not very robust and an advanced user could easily get to it again. Also, because a message such as 'X has been added to your shopping cart' appears at the top of the user's screen, and the 'shopping cart' part is a link to the cart, this wouldn't work.
• Use the uc_restrict_qty module to restrict the quantities. The uc_restrict_qty module is great and offers a simple menu-driven approach to restricting quantities, but this would rely on the site's administrator remembering to restrict quantities on each product in the store. We wanted all products to be restricted to a single item, so this seemed prone to human error.
• Disable the quantity field on the checkout pane but although this seemed like a sensible option, it turned out that overriding Ubercart's default display of the checkout was not easy, as it did not seem to abide by the usual Drupal theme functions. We didn't want to hack Ubercart core, because this would hinder future upgrades, so we sought a simpler solution.
• hook_form_alter the form responsible for the shopping cart which is uc_cart_view_form, and alter the #theme callback for all the quantity fields. By setting this to check_plain($element['#value']) it is possible to prevent the user from changing the value at all.

In the end, we utilised an Ubercart hook called hook_cart_item() which fires each time the cart is loaded. It checks the quantities of each item in the cart, and sets the quantity to 1 if it's not already 1. It's not the most elegant solution, but it does the job. Our implementation of the hook looked something like this:

It should be noted that this does not cater to the needs of the users, who will need to know that the shop imposes a 1-item limit. This will simply reset the quantity to 1 even if the user chooses more items, so unless there is a message to this effect somewhere on the site, the user might conclude that the site is not working properly.

We chose to implement a custom checkout pane with a special message to give the users some guidance, although perhaps that's a topic for an entirely separate article!