HQL中出现XXX is not mapped的错误

我的代码如下

    @Test
    public void testCollection(){
        String hql = "from Order  where orderItems is not empty";

        Query query =  session.createQuery(hql);

        List<Order> orders = query.list();

        for(Order o:orders){

            System.out.println(o.getCustomer().getName());

            System.out.println(o.getAmount());

        }

    }

由于没有在HQL语句中使用别名，而包里存在一个OrderItem的类，使其编译无法通过，所以将代码改写如下即可运行。

    @Test
    public void testCollection(){
        String hql = "from Order o where o.orderItems is not empty";

        Query query =  session.createQuery(hql);

        List<Order> orders = query.list();

        for(Order o:orders){

            System.out.println(o.getCustomer().getName());

            System.out.println(o.getAmount());

        }

    }