I recently had fun with an all-to-common issue with SQL driven websites: hierarchical data. For those who don’t like big words, think trees. Other people have already discussed storage methods, and I would actually highly suggest you read the writeup if you haven’t already.

While it is fairly straightforward to deal with, in our case we use HTML_QuickForm to handle our forms and are using QuickForm’s hierselect to select a category.

The issue starts showing its face in 2 distinct areas: (1) the client is not yet sure how deep they need their categories to go, and (2) the hierselect requires a very specific format of data to be passed in.