As you may be aware, all through the previous chapters, we never touch the core VirtueMart files. This is important in order to avoid headaches when we need to upgrade VirtueMart. If we modified the core files, they would be overwritten when upgrading and all our customizations will be lost. Obviously, this restriction limits our possibility of adding more useful functions to VirtueMart. Yet, we have to comply with this unless we would rather not do any upgrades or be willing to go to the trouble of updating our code whenever a new VirtueMart version comes out.
Starting from version 1.1.4, VirtueMart adds a new feature to allow us to write our own VirtueMart classes. This great enhancement is very similar to the templating system which allows us to supply our own template. As you may recall from Chapter 1, The VirtueMart Engine, VirtueMart classes are used to connect to the database and to provide underlying functions. Writing our own classes means we can...