for (User organizer : formEvent.getOrganizers()) {
organizersInDb.add(User.findById(organizer.id));
}
formEvent.getOrganizers().clear();
formEvent.getOrganizers().addAll(organizersInDb);
formEvent.saveManyToManyAssociations("organizers");
formEvent.update();
} else {
// Mise à jour d'un événement