@Override
 public StudentDocumentModel saveDocument(StudentDocumentModel model) throws ServiceException {
   // TODO Auto-generated method stub
   if (model.getId() == null) {
     model.setPostTime(new Date());
     studentDocumentDAO.saveOrUpdate(model);
   } else {
     model.setPostTime(new Date());
     studentDocumentDAO.merge(model);
   }
   return model;
 }