inanzzz | Logging field changes with a trigger like event listener for auditing purposes

Example below acts like pre-update database triggers where we log all activities made by users for auditing, reporting or security reasons. If someone changes the value from X to Y in a controller or a service class, this event listener records everything in another table in database.

Listeners.yml

services:
    application_backend.event_listener.user_entity_audit:
        class: Application\BackendBundle\EventListener\UserEntityAuditListener
        arguments: [ @security.context ]
        tags:
            - { name: doctrine.event_listener, event: preUpdate }
            - { name: doctrine.event_listener, event: postFlush }

UserEntityAuditListener

namespace Application\BackendBundle\EventListener;

use Application\BackendBundle\Entity\User;
use Application\BackendBundle\Entity\UserAudit;
use Doctrine\ORM\Event\PostFlushEventArgs;
use Doctrine\ORM\Event\PreUpdateEventArgs;
use Symfony\Component\Security\Core\SecurityContextInterface;

class UserEntityAuditListener
{
    private $securityContext;
    private $fields = ['username', 'password'];
    private $audit = [];

    public function __construct(SecurityContextInterface $securityContextInterface)
    {
        $this->securityContext = $securityContextInterface;
    }

    public function preUpdate(PreUpdateEventArgs $args) // OR LifecycleEventArgs
    {
        $entity = $args->getEntity();

        if ($entity instanceof User) {
            foreach ($this->fields as $field) {
                if ($args->getOldValue($field) != $args->getNewValue($field)) {
                    $audit = new UserAudit();
                    $audit->setField($field);
                    $audit->setOld($args->getOldValue($field));
                    $audit->setNew($args->getNewValue($field));
                    $audit->setUser($this->securityContext->getToken()->getUsername());

                    $this->audit[] = $audit;
                }
            }
        }
    }

    public function postFlush(PostFlushEventArgs $args)
    {
        if (! empty($this->audit)) {
            $em = $args->getEntityManager();

            foreach ($this->audit as $audit) {
                $em->persist($audit);
            }

            $this->audit = [];
            $em->flush();
        }
    }
}