Session.load()

最新推荐文章于 2022-07-03 14:35:48 发布

stonor

最新推荐文章于 2022-07-03 14:35:48 发布

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分类专栏： hibernate 文章标签： session integer hibernate exception 数据库 cache

本文链接：https://blog.youkuaiyun.com/stonor/article/details/1697236

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本文探讨了Hibernate中load与get方法的区别，特别是在处理数据库中存在与不存在的记录时的行为差异。通过示例展示了这两种方法如何与Session缓存交互。

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1。load一条不存在的记录
    Employee employee2 = (Employee) session.load(Employee.class, new Integer(100));
        会抛出net.sf.hibernate.ObjectNotFoundException。
    如果不想抛出该Exception, 应该使用session.get(Class clazz, Serializable id);

2. load一条数据库存在的记录
    1）如果session的Cache中存在，那么直接返回该引用。
    Session session = HibernateSessionFactory.currentSession();
        Transaction tx = session.beginTransaction();
        Employee employee1 = new Employee();
        employee1.setAge((byte)10);
        employee1.setBirthDay(new Date());
        employee1.setEmployeeName("HairRoot");
        employee1.setGender('m');
        employee1.setMarried(false);
        session.save(employee1);
        System.out.println(employee1);

        //employ1 已经被保存
    Employee employee2 = (Employee) session.load(Employee.class, new Integer(/*employee1.getId()*/100));
        System.out.println(employee2);
        tx.commit();
        session.close();

可以发现employee1和employee2是同一个引用。打开show_sql=true也会发现，hibernate并没有发送一条select语句给数据库。

    2）如果session的Cache中不存在，那么会立即发送一条select。
        Session session = HibernateSessionFactory.currentSession();
        Transaction tx = session.beginTransaction();
        Employee employee = (Employee) session.load(Employee.class, new Integer(100));
        System.out.println(employee);
        tx.commit();
        session.close();

后台:Hibernate: select employee0_.id as id0_, employee0_.age as age0_, employee0_.birthDay as birthDay0_, employee0_.employeeName as employee4_0_, employee0_.gender as gender0_, employee0_.married as married0_ from MWS_TEST_EMPLOYEE employee0_ where employee0_.id=?