Doctrine listener for audit log functionality

StudentChangeSubscriber.php

<?php

namespace Acme\StudentBundle\Listener;

use Doctrine\Common\EventSubscriber,
    Doctrine\ORM\Events,
    Doctrine\ORM\Event\OnFlushEventArgs,
    Doctrine\ORM\EntityManager,
    DoctrineExtensions\Versionable\Entity\ResourceVersion;

use Acme\StudentBundle\Entity\Student;
use Acme\StudentBundle\Entity\ActivityLog;

/**
 * Listens for changes on Student entity and reacts accordingly when certain
 * properties are changed.
 *
 * @author johnkary
 */
class StudentChangeSubscriber implements EventSubscriber
{
    public function getSubscribedEvents()
    {
        return array(Events::onFlush);
    }

    /**
     * @param OnFlushEventArgs $args
     */
    public function onFlush(OnFlushEventArgs $args)
    {
        /* @var $em \Doctrine\ORM\EntityManager */
        $em = $args->getEntityManager();
        /* @var $uow \Doctrine\ORM\UnitOfWork */
        $uow = $em->getUnitOfWork();

        /* @var $resourceClass Doctrine\ORM\Mapping\ClassMetadata */
        $resourceClass = $em->getClassMetadata('Acme\StudentBundle\Entity\ActivityLog');

        foreach ($uow->getScheduledEntityUpdates() as $entity) {
            if ($entity instanceof Student) {
                $entityClass = $em->getClassMetadata(get_class($entity));

                // Cannot use multi-column identifier
                $studentId = $entityClass->getIdentifierValues($entity);
                if (1 === count($studentId) && current($studentId)) {
                    $studentId = current($studentId);
                } else {
                    throw new \RuntimeException('A single identifier column is required.');
                }

                $oldValues = array_map(function($changeSetField) {
                    return $changeSetField[0];
                }, $uow->getEntityChangeSet($entity));

                // Don't need old ID anymore
                unset($oldValues[$entityClass->getSingleIdentifierFieldName()]);

                // Has the status field been changed?
                if ($this->hasChanged('status', $oldValues, $entity->getStatus())) {
                    $typeRepository = $em->getRepository('Acme\StudentBundle\Entity\ActivityLogType');
                    $statusChangeType = $typeRepository->findOneRootNodeByTitle('Status Change');
                    $manualType = $typeRepository->findOneChildByTitleWithDirectParent('Manual', $statusChangeType);

                    $message = sprintf('Status changed to "%s"', $entity->getStatus());

                    $activityLog = new ActivityLog();
                    // @TODO: Provide way to specify this or inject a subtype of ActivityLog to set below values on
                    $activityLog->setType($manualType);
                    $activityLog->setOccurredAt(new \DateTime('now'));
//                    $activityLog->setWho($currentUser);
                    $activityLog->setWho('Admin');
                    $activityLog->setDescription($message);

                    $em->persist($activityLog);

                    // Necessary instead of $em->flush() because we're already in flush process
                    $uow->computeChangeSet($resourceClass, $activityLog);
                }
            }
        }
    }

    /**
     * Checks if a given entity property has changed.
     *
     * @param string $propertyName  Name of entity property (e.g. $this->status should use 'status')
     * @param array $oldValues      Old values before they were changed
     * @param mixed $newValue       New value on the entity
     * @return boolean
     */
    private function hasChanged($propertyName, array $oldValues, $newValue)
    {
        if (!array_key_exists($propertyName, $oldValues)) {
            return false;
        }

        return $oldValues[$propertyName] != $newValue;
    }
}