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When published, any content item usually has at least one location, figured by its URL. Therefore Http cache being bound to URLs, if content A is updated (new version is published), we want Http cache for all its locations to be cleared, so the content itself can appear up-to-date everywhere it is supposed to be displayed. Sometimes, clearing cache for the content's locations is not sufficient. You can for instance have an excerpt of it displayed in a list from the parent location, or from within a relation. In this case, cache for the parent location and/or the relation need to be cleared as well (at least if an ESI is not used).
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Smart Http cache clearing is an event based mechanism. Whenever a content item needs its cache to be cleared, the cache purger service sends an ezpublish.cache_clear.content event (also identified by eZ\Publish\Core\MVC\Symfony\MVCEvents::CACHE_CLEAR_CONTENT constant) and passes a eZ\Publish\Core\MVC\Symfony\Event\ContentCacheClearEvent event object. This object contains the ContentInfo object we need to clear the cache for. Every listener for this event can add location objects to the cache clear list.
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Important: Cache clear listener services must be tagged as ezpublish.http_cache.event_subscriber or ezpublish.http_cache.event_listener. |
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namespace Acme\AcmeTestBundle\EventListener;
use eZ\Publish\API\Repository\LocationService;
use eZ\Publish\Core\MVC\Symfony\Event\ContentCacheClearEvent;
use eZ\Publish\Core\MVC\Symfony\MVCEvents;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
class ArbitraryLocationsListener implements EventSubscriberInterface
{
/**
* @var LocationService
*/
private $locationService;
public function __construct( LocationService $locationService )
{
$this->locationService = $locationService;
}
public static function getSubscribedEvents()
{
return [MVCEvents::CACHE_CLEAR_CONTENT => ['onContentCacheClear', 100]];
}
public function onContentCacheClear( ContentCacheClearEvent $event )
{
// $contentInfo is the ContentInfo object for the content being cleared.
// You can extract information from it (e.g. ContentType from its contentTypeId), using appropriate Repository services.
$contentInfo = $event->getContentInfo();
// Adding arbitrary locations to the cache clear list.
$event->addLocationToClear( $this->locationService->loadLocation( 123 ) );
$event->addLocationToClear( $this->locationService->loadLocation( 456 ) );
}
} |
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parameters:
acme.cache_clear.arbitrary_locations_listener.class: Acme\AcmeTestBundle\EventListener\ArbitraryLocationsListener
services:
acme.cache_clear.arbitrary_locations_listener:
class: %acme.cache_clear.arbitrary_locations_listener.class%
arguments: [@ezpublish.api.service.location]
tags:
- { name: ezpublish.http_cache.event_subscriber }
|