Zen Cart Rule #3: Don’t Over-Prepare

 hints, php, troubleshoot, zen-cart  Comments Off on Zen Cart Rule #3: Don’t Over-Prepare
Oct 312015

When you’re performing database manipulations, it’s important to prepare your textual input so that there aren’t any stray single- (‘) or double-quotes  (“) that will wreck havoc with your MySQL queries.  Zen Cart provides methods (the functions zen_db_input and $db->prepare_input) that will help, but you need to have a plan for what method you’re going to use to insert or update that data to prevent over-preparation.

Zen Cart provides two methods for inserting and updating database information:

  1. class-based, using the $db->Execute function.
  2. function-based, using the zen_db_perform function.

The class-based method allows you full control over the formatting of a MySQL query while the function-based method uses an associative input-array to map each database field to its associated value.  The function-based method’s strength is its ease in creating or updating an entire database table record, while the class-based method is more suitable to a quick update of a couple of fields in a record.

When you use the class-based method, it’s very important to prepare any text input prior to sending that data to the database, i.e. escaping any quotes within the data.  Failure to do this can result in a whitescreen (with associated myDEBUG*.log) intermittently … based on the data input.

When you use the function-based method, that function automatically prepares all input — in fact, it treats all input as strings.  If you’ve also prepared the input, the resultant database field will include unwanted slashes (e.g. o/’Toole instead of o’Toole).  That’s because the function has prepared (via call to $db->prepare_input) data that you’ve already prepared, resulting in the slashes themselves being escaped … a result of over-preparation!

Zen Cart makes it easy to perform your database manipulations, but the onus is on you to first choose the method that you’re going to use and then perform any input-preparations needed based on the method you’ve chosen.

Zen Cart Rule #2: Additional Images’ Names

 hints, troubleshoot, zen-cart  Comments Off on Zen Cart Rule #2: Additional Images’ Names
Sep 292015

From “Animal Farm”, by George Orwell:

All animals are equal, but some are more equal than others.

You’ve got your Zen Cart set up and have been placing all your products’ images in the base images’ folder (/images). It’s getting hard to maintain all those images in a single folder (and it’s surely increasing your page-load times), so you’ve decided to move all the product images into manufacturer-based sub-directories.

Good plan! Now you’ve updated each of the products’ database records to properly point to the primary image that’s now in an images’ sub-directory (e.g. images/microsoft) and have copied all those additional product images as well. You fire up your store with those relocated images and … what the heck … many of your additional images have “gone missing”. You re-check that the additional-image files have, in fact, been copied to their manufacturer sub-directory — they’re there!

One of the “problem” products uses base image name of my_image.jpg and it’s got two additional images: my_image-01.jpg and my_image-02.jpg. There’s the issue — all additional images are equal, but some are more equal than others!

The additional-images’ handling (/includes/modules/additional_images.php) uses different criteria when the base image is in a sub-directory than in the main /images directory!  When a main product image is in a sub-directory, its additional images’ file-names are of the form base_suffix.ext; when the main image is in the root /images directory, no intervening underscore is required.

So, given the example above, the file my_image-01.jpg is a perfectly-acceptable additional image for the file my_image.jpg … when the main image is in the /images directory itself … but not when the main image is in a sub-directory.  The file my_image_01.jpg is a valid additional image for my_image.jpg, regardless the directory in which the main image resides.

Now that you know the additional-images’ naming rules, it’s easier to play the game! Happy Zenning!

Zen Cart Rule #1: Shipping Module Names

 hints, php, troubleshoot, zen-cart  Comments Off on Zen Cart Rule #1: Shipping Module Names
Aug 282015

There are rules everywhere.  In the kitchen, my #1 rule is “Never try to catch a falling knife“; it apparently applies to investments, too!  In Zen Cart, my current #1 rule (having spent an inordinate amount of time debugging its misuse) is “Never use an underscore (_) in a shipping module’s name“.

A shipping module (unlike a payment or order-total module) can have multiple methods that it supports, so the built-in Zen Cart processing uses an underscore (_) to record both the Shipping Module and Shipping Method chosen for an order as a single string value.  For example, using Zen Cart v1.5.4, the Store Pickup shipping module supports multiple stores.  When the customer chooses the first store location, the id associated to the shipping selection is storepickup_storepickup0.

Once the shipping selection is made, the Zen Cart processing maps that selection back to the Store Pickup module (storepickup.php) and its storepickup0 method by splitting (via the PHP explode function) that id value at the (presumed single) underscore.  If there’s an underscore in the shipping module’s name, the association between the shipping module and selected method can never be resolved so the customer is always redirected back to the checkout_shipping page (with no message).

Repeat after me:  I will never (again) use an underscore in a shipping module’s name.