@Override
 public Student getByName(String name, String surname) throws RepositoryException {
   for (Student st : students) {
     if (st.getName().equals(name) && st.getName().equals(surname)) return st;
   }
   return null;
 }
 @Override
 public void update(Student obj) {
   Student st = this.getByID(obj.getID());
   st.setDb(null);
   try {
     st.setName(obj.getName());
   } catch (RepositoryException e) {
     // TODO Auto-generated catch block
     e.printStackTrace();
   }
   st.setDb(this.db);
 }