hibernate_day04_05_hql查询（排序查询）和06_hql查询（分页查询和投影查询）

排序查询
1 hql排序语句写法
（1）from 实体类名称 order by 实体类属性名称 asc/desc

//Query query = session.createQuery("from Customer order by cid asc");//默认升序Query query = session.createQuery("from Customer order by cid desc");

 

//排序@Testpublic void testSelect4(){SessionFactory sessionFactory = null;Session session = null;Transaction tx = null;try{sessionFactory = HibernateUtils.getSessionFactory();session = sessionFactory.openSession();tx = session.beginTransaction();//1 创建query对象//Query query = session.createQuery("from Customer order by cid asc");//默认升序Query query = session.createQuery("from Customer order by cid desc");//2调用方法得到结果List<Customer> list = query.list();for (Customer customer : list) {System.out.println(customer.getCid()+":::"+customer.getCustName());}tx.commit();}catch(Exception e){tx.rollback();}finally{session.close();sessionFactory.close();}}

06_hql查询（分页查询和投影查询）

1 mysql实现分页

（1）使用关键字 limit实现

 

2在hql中实现分页

（1）在hql操作中，在语句里面不能写limit，hibernate的Query对象封装两个方法实现分页操作

//1 创建query对象Query query = session.createQuery("from Customer");//2 设置分页数据//2.1 设置开始位置query.setFirstResult(3);//2.2 设置每页记录数query.setMaxResults(3);//3调用方法得到结果List<Customer> list = query.list();

//分页@Testpublic void testSelect5(){SessionFactory sessionFactory = null;Session session = null;Transaction tx = null;try{sessionFactory = HibernateUtils.getSessionFactory();session = sessionFactory.openSession();tx = session.beginTransaction();//1 创建query对象Query query = session.createQuery("from Customer");//2 设置分页数据//2.1 设置开始位置query.setFirstResult(3);//2.2 设置每页记录数query.setMaxResults(3);//3调用方法得到结果List<Customer> list = query.list();for (Customer customer : list) {System.out.println(customer.getCid()+":::"+customer.getCustName());}tx.commit();}catch(Exception e){tx.rollback();}finally{session.close();sessionFactory.close();}}

投影查询

1 投影查询：查询不是所有字段值，而是部分字段的值


2 投影查询hql语句写法：
（1）select 实体类属性名称1, 实体类属性名称2  from 实体类名称
（2）select 后面不能写 * ，不支持的


3 具体实现
 

//投影@Testpublic void testSelect6(){SessionFactory sessionFactory = null;Session session = null;Transaction tx = null;try{sessionFactory = HibernateUtils.getSessionFactory();session = sessionFactory.openSession();tx = session.beginTransaction();//1 创建query对象Query query = session.createQuery("select custName from Customer");//2调用方法得到结果List<Object> list = query.list();for (Object object : list) {System.out.println(object);}tx.commit();}catch(Exception e){tx.rollback();}finally{session.close();sessionFactory.close();}}