码迷,mamicode.com
首页 > Web开发 > 详细

hibernate学习6_session之clear与flush

时间:2015-01-29 01:19:13      阅读:179      评论:0      收藏:0      [点我收藏+]

标签:

1、session的clear()方法

  hibernate从数据库中get或load记录时,或先去session一级缓存中查找对应数据,如果缓存中没有记录,则去对应数据库中查询,

如果有记录则直接从缓存中获取。

    public void testClear() {
        Session session1 = sf.getCurrentSession();
        session1.beginTransaction();
        Student t1 = (Student) session1.get(Student.class, 45);
        //session1.clear();
        Student t2 = (Student) session1.get(Student.class, 45);
        session1.getTransaction().commit();
    }

执行时只会发出一次查询

Hibernate: select student0_.id as id1_0_0_, student0_.age as age2_0_0_, student0_.name as name3_0_0_ from Student student0_ where student0_.id=?

加上session的clear()方法后,会清空当前session缓存,数据库查询两次,如下:

Hibernate: select student0_.id as id1_0_0_, student0_.age as age2_0_0_, student0_.name as name3_0_0_ from Student student0_ where student0_.id=?
Hibernate: select student0_.id as id1_0_0_, student0_.age as age2_0_0_, student0_.name as name3_0_0_ from Student student0_ where student0_.id=?

 

2、session的flush方法

flush方法会强制同步当前session缓存数据至数据库中,如下:

    @Test
    public void testFlush() {
        Session session1 = sf.getCurrentSession();
        session1.beginTransaction();
        Student t1 = (Student) session1.get(Student.class, 45);
        t1.setAge(30);
        t1.setAge(40);
        session1.getTransaction().commit();
    }

此时数据库中load出对应记录后,虽然前后连续更改了两次属性,数据库只执行一次update

Hibernate: update Student set age=?, name=? where id=?

加上flush后:

    public void testFlush() {
        Session session1 = sf.getCurrentSession();
        session1.beginTransaction();
        Student t1 = (Student) session1.get(Student.class, 45);
        t1.setAge(30);
        session1.flush();
        t1.setAge(40);
        session1.getTransaction().commit();
    }

数据库连续执行两次update

Hibernate: update Student set age=?, name=? where id=?
Hibernate: update Student set age=?, name=? where id=?

 

hibernate学习6_session之clear与flush

标签:

原文地址:http://www.cnblogs.com/toDjlPersonnalBlog/p/4257705.html

(0)
(0)
   
举报
评论 一句话评论(0
登录后才能评论!
© 2014 mamicode.com 版权所有  联系我们:gaon5@hotmail.com
迷上了代码!