@Listen("onClick = #addBtn")
public void add() throws InterruptedException {
Node node = nodeList.getSelectedItem().getValue();
node = nodeDao.loadById(node.getId());
AbstractQuestionRelation p = (AbstractQuestionRelation) getParent();
node.getGroups().addAll((p.getQuestion().getAvailableGroups()));
nodeDao.save(node);
// update interface
p.refreshWholePage();
}