问原则2-可在插入时确认

EN

public function onFlush(OnFlushEventArgs $args)
{
    $em = $args->getEntityManager();
    $uow = $em->getUnitOfWork();

    foreach ($uow->getScheduledEntityInsertions() AS $entity) {
        if ($entity instanceof Versionable) {
            $this->_makeSnapshot($entity);
        }
    }

    foreach ($uow->getScheduledEntityUpdates() AS $entity) {
        if ($entity instanceof Versionable) {
            $this->_makeSnapshot($entity);
        }
    }
}