Drupal hooks

Hooks are little blocks of functionality, called functions, that contain PHP code. These blocks of code run when they are called upon. During the bootstrapping process, especially when the final “which page?” question is asked, hooks are called. Whenever an event happens in Drupal, like deleting a page, hooks are called. Inside those hooks, there is code that alters functionality, and it runs as soon as the hook is called. Almost anything you want Drupal to do has a hook doing it.

Drupal relies on naming conventions to call hooks when the time is right for them to run. While building the menu, Drupal looks for hooks with “_menu” in the name. When a page is deleted, hooks with the name “_delete” are called.• Drupal already does what you want it to do because the necessary hooks, with the necessary code, run by default.

• Drupal provides an administrative interface for you to turn it on or change it.

• A module or theme already has been written, calling or adding the hooks (with the necessary code inside them) that you need.

• Custom code must be written (using or creating hooks and adding code to them). The time and effort required here varies widely, from three quickly written lines of code to months of programming, creating multiple contributable modules.

• Custom database tables must be created. At this level of complexity, the code still will rely on hooks but begins to run outside of what Drupal does natively; therefore, it is (sometimes) more complex than adding code alone.

• Necessary data comes from other Web sites, or your site’s new feature requires communicating with other sites (for example, credit-card processing). The time and effort to do this also varies widely and can be as easy as adding a module (that already handles this communicating) or as hard as writing a separate application that runs when the appropriate hook is called. What your site will do with the data and the load it puts on the system greatly influences the complexity as well.

• Your tasks can’t run on page load, a special process has to be written to accomplish them. Sometimes, this is a quick addition (a simple cron job using hook_cron), and sometimes this is complicated. Often, this approach is used when data processing would slow page load down (or take down the site), so it is handled out of sync and saved (cached), serving the cached version when the page loads and the question is asked.

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