求解：hibernate session.get(Class clazz,Serializable id)返回空值

public static void testUpdate1() {

Session session = sessionFactory.getCurrentSession();
session.beginTransaction();
Teacher t = (Teacher)session.get(Teacher.class, 1);
System.out.println(t);//t返回为空；为什么》？？？
session.getTransaction().commit();

t.setName("zhanglaoshi");

Session session2 = sessionFactory.getCurrentSession();
session2.beginTransaction();
session2.update(t);

session2.getTransaction().commit();
}

希望高手指点，谢谢

public static void testUpdate1() {

Session session = sessionFactory.getCurrentSession();
session.beginTransaction();
Teacher t = (Teacher)session.get(Teacher.class, 1);//谁知道 你的ID 有没有 1的
System.out.println(t);//t返回为空；为什么》？？？
session.getTransaction().commit();//查询用不着事务

t.setName("zhanglaoshi");

Session session2 = sessionFactory.getCurrentSession();
session2.beginTransaction();
session2.update(t);

session2.getTransaction().commit();
}