public void Delete(Produto obj) throws Exception {
   try {
     transaction = manager.getTransaction();
     transaction.begin();
     manager.remove(obj);
     transaction.commit();
   } catch (Exception ex) {
     transaction.rollback();
     throw ex;
   }
 }
 public Produto Open(int id) throws Exception {
   try {
     return manager.find(Produto.class, id);
   } catch (Exception ex) {
     throw ex;
   }
 }