gistfile1.txt

class DDC1020OrderEventListener
{
    public function preUpdate(LifecycleEventArgs $args)
    {
        $order = $args->getEntity();
        $order->tax = 100;
        $em = $args->getEntityManager();
        $uow = $em->getUnitOfWork();
        $uow->recomputeSingleEntityChangeSet(
            $em->getClassMetadata(get_class($order)),
            $args->getEntity()
        );
    }
}