hibernate--session的CRUD方法, delete, load,get,update,saveorupdate, clear, flush

• 删除方法:

新建的对象立马被删除

@Test
	public void testDelete() {

		Teacher t = new Teacher();
		t.setName("t1");
		t.setTitle("middle");
		t.setBirthDate(new Date());

		Session session = sessionFactory.getCurrentSession();
		session.beginTransaction();
		session.save(t);
		System.out.println(t.getId());
		session.getTransaction().commit();

		Session session2 = sessionFactory.getCurrentSession();
		session2.beginTransaction();
		session2.delete(t);
		session2.getTransaction().commit();
	}

　

删除指定ID的对象:

	@Test
	public void testDelete2() {

		Teacher t = new Teacher();
		t.setId(2);

		Session session2 = sessionFactory.getCurrentSession();
		session2.beginTransaction();
		session2.delete(t);
		session2.getTransaction().commit();
	}

　　

• load, get区别:

load返回的代理对象, 真正用到对象时才发出sql语句,

get直接从数据库加载,发出sql语句, 不会延迟.

所以load必须在commit之前执行getName方法的操作.

但是get放在commit之前之后都可以.

@Test
	public void testLoad() {

		Session session = sessionFactory.getCurrentSession();
		session.beginTransaction();
		Teacher t = (Teacher)session.load(Teacher.class, 1);  //此数字是ID

		System.out.println(t.getName());
		session.getTransaction().commit();
		//System.out.println(t.getClass());
	}

	@Test
	public void testGet() {

		Session session = sessionFactory.getCurrentSession();
		session.beginTransaction();
		Teacher t = (Teacher)session.get(Teacher.class, 1);

		session.getTransaction().commit();
		//System.out.println(t.getClass());
		System.out.println(t.getName());
	}

update:

第一种情况: 用给的detached对象来更新persistent对象.

@Test
	public void testUpdate1() {

		Session session = sessionFactory.getCurrentSession();
		session.beginTransaction();
		Teacher t = (Teacher)session.get(Teacher.class, 1);  //persistent

		session.getTransaction().commit();

		t.setName("zhanglaoshi");  //commit后, detached

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

		session2.getTransaction().commit();
	}

第二种情况:更新transient对象会报错

@Test
	public void testUpdate2() {
		Teacher t = new Teacher();
		t.setName("zhanglaoshi");
		Session session2 = sessionFactory.getCurrentSession();
		session2.beginTransaction();
		session2.update(t);
		session2.getTransaction().commit();
	}

第三种情况, 手动设置ID后update, 数据库有对应记录

@Test
	public void testUpdate3() {
		Teacher t = new Teacher();
		t.setId(3);
		t.setName("zhanglaoshi");

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

		session2.getTransaction().commit();
	}

　　

第四种情况: 我们在update的时候, 没有设置别的字段, 但是控制台把所有字段都输出了,效率低下.

一个persistent状态的对象只要设定不同字段,  就会更新:

@Test
　　public void testUpdate4() {
	Session session = sessionFactory.getCurrentSession();
	session.beginTransaction();
	Teacher t = (Teacher)session.get(Teacher.class, 1);  //Persistent状态
	t.setName("zhangsan2");  //缓存和数据库内容不一致, commit时统一
	session.getTransaction().commit();
　　}

　　

最后都没有得到我们想要的效果: 只更新想改变的字段, 有3种方法:

1. xml和annotation设置

annotation方法:Teacher.java里不想更新的字段的get方法前,加入@Column(updatable=false)

xml方法:  <property name="title" update=false> </property>

2. 使用xml的dynamic-update,

<hibernate-mapping>
	<class name="com.bjsxt.hibernate.Student" dynamic-update="true">

3. 推荐!!!  HQL (EJBQL)

注意: update后面的Student是对象, 不是表名

@Test
　　public void testUpdate7() {
	Session session = sessionFactory.getCurrentSession();
	session.beginTransaction();
	Query q = session.createQuery("update Student s set s.name='z5' where s.id = 1");
	q.executeUpdate();
	session.getTransaction().commit();
　　}

　　

saveorupdate:

@Test
	public void testSaveOrUpdate() {

		Teacher t = new Teacher();
		t.setName("t3");
		t.setTitle("middle");
		t.setBirthDate(new Date());

		Session session = sessionFactory.getCurrentSession();
		session.beginTransaction();
		session.saveOrUpdate(t);  //没有id所以执行的是save

		session.getTransaction().commit();

		t.setName("t7");

		Session session2 = sessionFactory.getCurrentSession();
		session2.beginTransaction();
		session2.saveOrUpdate(t);  //将上面插入的t3update成t7
		session2.getTransaction().commit();

	}

clear方法: 清除缓存, 不喝数据库打交道.  如果不用clear的话, getName就调用一次select语句, 因为缓存已经存在了

不管get还是load都会先查一级缓存, 缓存没有才会去数据库查找, 所以clear就是清除session缓存

@Test
	public void testClear() {

		Session session = sessionFactory.getCurrentSession();
		session.beginTransaction();
		Teacher t = (Teacher)session.load(Teacher.class, 4);
		System.out.println(t.getName());

		session.clear();

		Teacher t2 = (Teacher)session.load(Teacher.class, 4);
		System.out.println(t2.getName());
		session.getTransaction().commit();	

	}

　　

flush方法: 强制内存到数据库的同步

	@Test
	public void testFlush() {

		Session session = sessionFactory.getCurrentSession();
		session.beginTransaction();
		Teacher t = (Teacher)session.load(Teacher.class, 4);
		t.setName("tt");		

		session.flush();
		t.setName("ttt");
		session.getTransaction().commit();
	}