Drupal 7 Module Development

Chapter 1
While one could imagine that comments are merely a type of node (and, in fact, there
are modules that do this), Drupal developers have chosen to implement comments
as a separate type. The comment module contains the majority of the comment code.
However, again, as with the node system, it provides numerous hooks, and thus
many other modules interact with the comment system.
Fields and entities
In previous versions of Drupal, the node system was really the only system for
creating structured pieces of textual content. (Comments are too focused to be
generally useful for extension.) In order to extend node content beyond simple title
and body fields, one needed to either write custom node types or use the Content
Construction Kit (CCK) to build node types.
However, Drupal 7 introduces two substantial subsystems that change this:
• The fields system brings most of CCK's functionality into core
• The entities system makes it possible to define other structured data types
that are not nodes
Already these new systems are making waves among Drupal developers, with the
Drupal Commerce module leading the way in defining sophisticated entities that
are not nodes.
These two subsystems are new, important, and also complex. So we will cover them
in detail in Chapter 6.
Forms API
Another remarkable subsystem that is provided in Drupal's core is the Forms API
(FAPI). This system provides a robust programmatic tool for defining, displaying,
validating, and submitting forms. It takes much of the busy-work out of developing
forms, and also adds a layer of security. FAPI is so integral to Drupal that we use it
numerous times throughout the book.
Installation Profiles
More sophisticated Drupal use-cases may benefit from the ability to customize the
installation process. Drupal provides an installation profile subsystem that can be
leveraged to create a custom installer.
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