javax.persistence.NoResultException:No entity Found for query 异常的解决办法

        Query query = getEntityManager().createQuery("from DataFile d where d.fileName=:fileName");
        query.setParameter("fileName", fileName);
         return (DataFile) query.getSingleResult();

 

        Query query = getEntityManager().createQuery("from DataFile d where d.fileName=:fileName");
        query.setParameter("fileName", fileName);
        if (query.getResultList().size() == 0) {
            return null;
        } else {
            return (DataFile) query.getSingleResult();
        }