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Events

When to Use

When you need to hook into the facets processing pipeline without creating a full custom processor.

Decision: Available Events

Event Constant Class When Dispatched Use Case
QUERY_STRING_CREATED QueryStringCreated After building URL query string Modify URL parameter format
ACTIVE_FILTERS_PARSED ActiveFiltersParsed After parsing URL parameters Override active filter detection
URL_CREATED UrlCreated After building facet link URL Modify individual link destinations
POST_BUILD_FACET PostBuildFacet After complete BUILD stage Final modifications to rendered facet
GET_FACET_CACHE_CONTEXTS GetFacetCacheContexts During cache metadata collection Add/override cache contexts
GET_FACET_CACHE_MAX_AGE GetFacetCacheMaxAge During cache metadata collection Override cache max age
GET_FACET_CACHE_TAGS GetFacetCacheTags During cache metadata collection Add/override cache tags

Pattern: Subscribing to Events

# my_module.services.yml
services:
  my_module.facets_subscriber:
    class: Drupal\my_module\EventSubscriber\FacetsSubscriber
    tags:
      - { name: event_subscriber }

namespace Drupal\my_module\EventSubscriber;

use Drupal\facets\Event\FacetsEvents;
use Drupal\facets\Event\QueryStringCreated;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;

class FacetsSubscriber implements EventSubscriberInterface {

  public static function getSubscribedEvents(): array {
    return [
      FacetsEvents::QUERY_STRING_CREATED => 'onQueryStringCreated',
    ];
  }

  public function onQueryStringCreated(QueryStringCreated $event): void {
    // Modify the query string parameters.
    $filter_params = $event->getFilterParameters();
    // ... modify $filter_params
    $event->setFilterParameters($filter_params);
  }

}

Common Mistakes

  • Writing a custom processor just to tweak a URL format — Subscribe to QUERY_STRING_CREATED or URL_CREATED instead — no plugin boilerplate needed.

See Also