hibernate在evict()后为什么还会同步数据库

[Rick____]

Student s = new Student("stu1");
		SessionFactory sf = HibernateUtils.getSessionFactory();
		Session session = sf.openSession();
		session.beginTransaction();
		session.save(s);
		session.evict(s);
		session.getTransaction().commit();
		session.close();
		sf.close();

evict看文档的意思是在session缓存里把persistent状态对象移除,之后事务commit()中flush()会同步session缓存中所有对象,但为什么以上代码还会产生insert语句,并持久化到数据库中?