MediaWiki Hook for Installing Extension - mediawiki

Question

I did some research on MediaWiki hooks.
To the best of my knowledge, the only hook for adding/updating database tables is https://www.mediawiki.org/wiki/Manual:Hooks/LoadExtensionSchemaUpdates.
However, I need a hook that fires on installing a new extension. How do I achieve that? I'd like to execute a CREATE TABLE statement only once - when the extension is installed. Installing an extension doesn't require a MediaWiki update, which is why the above hook does not suit my needs.
EDIT
To clarify: I'm developing an extension that requires access to a custom table in the database. That's why I need to execute the CREATE TABLE statement whenever this extension is installed.

Answer 1

First: As you have noticed, there is no such hook. You will need to do the check for installed extensions by a cron job (if it's your server), or on, say, each 100th request to the wiki, using the job queue (if you are doing this in an extension).
From there, you have a few options, depending on if you need to catch every single extension, or just most of them:
Check for registered extensions, with something like: $registry = ExtensionRegistry::getInstance();$extensions = $registry->loaded();This will work extensions using the new style. For older versions, check the global variable $wgExtensionCredits for registered extensions. Note that nothing prevents an extensions from running without registering. In fact, there are a lot of extensions like that.
Parse LocalSettings.php, and check for old and new style extension loading with a regex. Very dirty, but it's actually the way e.g. the maintainance script getConfiguration.php does it. You need to check for lines like this:wfLoadExtension( 'FooBar' );and this:wfLoadExtensions( ['Foo', 'Bar'] );and this:require_once "$IP/extensions/Foo/Bar.php"; Note however that it is possible to use other directories for extensions, and that modern skins in fact behave like extensions too.
If you need to track a certain family of extensions, and you can make sure they all use Composer, the parse $IP/composer.json for installed extensions.

Answer 2

I did some more research (https://www.mediawiki.org/wiki/Manual:Update.php#Details) and found out that the LoadExtensionSchemaUpdates hook is exactly what I am looking for.
# Schema updates for update.php
$wgHooks['LoadExtensionSchemaUpdates'][] = 'fnMyHook';
function fnMyHook( DatabaseUpdater $updater ) {
$updater->addExtensionTable( 'tablename',
__DIR__ . '/table.sql' );
return true;
}
When running $ php update.php for the first time after installing the extension, the script executes the CREATE TABLE statement. Then, for consecutive executions, the update script just notes that the table already exists.