ObjectSet<Persona> set =
    db.queryByExample(new Persona(null, "A", 0));
    //db.queryByExample(new Persona(null, null, 30));
    //db.queryByExample(new Persona(null, null, 0));

    for (Persona p : set) {
        System.out.println(p.nom);
        db.delete(p);
   }

    db.close();