(6)hibernate CURD
1. 获取session,SessionFactory sf = new AnnotationConfiguration().configure().buildSessionFactory();
A.Session session = sf.openSession();
B.Session session = sf.getCurrentSession();
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说明：第一种每次都打开一个新连接,要显示关闭.
???????? 第二种，先从上下文查看有没有session,有就用它没有创建一个新的，一旦commit().就会自动关闭连接，在配置文件中hibernate.cfg.xml 要加入?? <property name="current_session_context_class">thread</property>也可能用jta.
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2. save
Session session = sf.openSession();
??session.beginTransaction();
??session.save(s);
??session.getTransaction().commit();
? session.close();
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下面可能看出session的关系:
Teacher t = new Teacher();
??t.setName("王老师");
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??Session session = sf.getCurrentSession();
??session.beginTransaction();
??session.save(t);
??Session session2 = sf.getCurrentSession();
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??System.out.println(session == session2);
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??session.getTransaction().commit(); //提交之后此session关闭
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??Session session3 = sf.getCurrentSession();
??System.out.println(session == session3);
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3. delete
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Teacher t = new Teacher();
??t.setName("Miss Wang");
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??Session session = sf.getCurrentSession();
??session.beginTransaction();
??session.save(t);
??System.out.println(t.getId());
??session.getTransaction().commit();
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??Session session2 = sf.getCurrentSession();
??session2.beginTransaction();
??session2.delete(t);
??session2.getTransaction().commit();
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其实只要Id与DB中的Id对应就可以删除,不用管对象处在哪种状态.
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4.Load
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Session session = sf.getCurrentSession();
??session.beginTransaction();
??Teacher? t = (Teacher)session.load(Teacher.class, 2);
??System.out.println(t.getName());
??session.getTransaction().commit();
??System.out.println(t.getClass());
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查出来的对象是一个代理类，只有去查类中的属性才会真正去查数据库.
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5. Get
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Session session = sf.getCurrentSession();
??session.beginTransaction();
??Teacher t = (Teacher)session.get(Teacher.class, 2);
??session.getTransaction().commit();
??System.out.println(t.getName());
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不会产生廷迟加载，立即查询数据库.
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6. Update
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下面列举4种:
A.? update
Session session = sf.getCurrentSession();
??session.beginTransaction();
??Teacher t = (Teacher)session.get(Teacher.class, 2);
??session.getTransaction().commit();
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??t.setName("李老师");
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??Session session2 = sf.getCurrentSession();
??session2.beginTransaction();
??session2.update(t);
??session2.getTransaction().commit();
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B.
Session session = sf.getCurrentSession();
??session.beginTransaction();
??Teacher t = (Teacher)session.get(Teacher.class, 2);
??t.setName("白老师");
??session.getTransaction().commit();
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C.? HQL
Session session = sf.getCurrentSession();
??session.beginTransaction();
??Query query = session.createQuery("update Teacher set name='小明' where id=2");
??query.executeUpdate();
??session.getTransaction().commit();
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D.? 合并
Session session = sf.getCurrentSession();
??session.beginTransaction();
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??Teacher t = (Teacher)session.get(Teacher.class, 2);
??session.getTransaction().commit();
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??t.setSex("女");
??Session session2 = sf.getCurrentSession();
??session2.beginTransaction();
??session2.merge(t);
??session2.getTransaction().commit();
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说明：如果没有做什么设置，除了C以外，其它的更新操作如果你只是对其中一个字段更新hibernate还是会默认更新所有字段,解决方案有使用B或D，在xx.hbm.xml文件中，加入动态更新设置,如下
<class name="Teacher" dynamic-update="true">
??<id name="id">
???<generator class="native"/>
??</id>
??<property name="name"/>
??<property name="sex"/>
?</class>
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这样只有要更新的字段才会更新，对于D方案还要提一下，当session提交之后对象处于detached,使用merget()方法，它会先去数据库先查一下放在缓存中与对象比较，然后才能判断哪个字段需要更新.
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7. SaveOrUpdate
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Teacher t = new Teacher();
??t.setName("XY");
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??Session session = sf.getCurrentSession();
??session.beginTransaction();
??session.saveOrUpdate(t);
??session.getTransaction().commit();
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??t.setName("JJ");
??Session session2 = sf.getCurrentSession();
??session2.beginTransaction();
??session2.saveOrUpdate(t);
??session2.getTransaction().commit();
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8. Clear 清除缓存
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Session session = sf.getCurrentSession();
??session.beginTransaction();
??Teacher t1 = (Teacher)session.load(Teacher.class, 3);
??System.out.println(t1.getName());
??System.out.println(t1.getSex());
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??session.clear();
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??Teacher t2 = (Teacher)session.load(Teacher.class, 3);
??System.out.println(t2.getName());
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??session.getTransaction().commit();
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?9.Flush
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Session session = sf.getCurrentSession();
??session.beginTransaction();
??Teacher t = (Teacher)session.load(Teacher.class, 2);
??t.setName("ss");
??session.flush();
??t.setName("mm");
??session.getTransaction().commit();
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10. SchemaExport
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new SchemaExport(new AnnotationConfiguration().configure()).create(true, false);
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说明:create(true,false)第一个boolean代表是否输出ddl，第二个，是否同步数据库.
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