Writing a Module

Modules are the basic building blocks that form the foundation of Drupal and are the mechanisms for extending the functionality provided by the off-the-shelf version of Drupal, also known as Drupal core. I often explain to those who are unfamiliar with Drupal that modules are like Lego building blocks. They fit together perfectly by following a predefined set of guidelines, and with a combination of modules, you can build rich and complex solutions.  

There are two general categories of Drupal modules — core and contributed. Core modules are those that are shipped with Drupal and include modules such as polls, menus, taxonomy, search, feed aggregator, and forums. Contributed modules are all of the modules created by the community that extend and enhance the functional footprint of Drupal core. There are literally thousands of contributed modules available for download at http://drupal.org/project/modules and span everything from simple single task modules, such as displaying the current date and time, to complex solutions, such as an e-commerce storefront.  

In this chapter, I will show you how to build a custom module from scratch. As you build the module, you’ll learn about the standards to which modules must adhere. I need a realistic goal, so let’s focus on the real-world problem of annotation. When looking through the pages of a Drupal web site, you may want to write a note about that page. We could use Drupal’s comments feature to accomplish this, but comments are typically viewable by anyone visiting the site, or authenticated users. Annotations, on the other hand, are viewable only by the node’s author.