Update hooks

At the beginning of this chapter, we defined two tables using hook_schema(), which got installed together with the module. To reiterate, if the module had already been installed, we could have triggered the schema installation using the drupal_install_schema() function. However, what if we needed to add another column later on, say to the teams table? Our module is installed, and so is the schema; we cannot exactly uninstall it on production just to trigger the schema creation again. Luckily, there is a system in place for this, namely, update hooks—hook_update_N()—where N represents the schema version. These are sequentially named hook implementations that go inside the module *.install file and that are triggered when running the updates, either by going to /update.php or by using the drush updatedb command.

The main purpose of these update hooks is to make schema alterations to existing database tables.

Note

If you remember, when we were talking...