Hibernater学习笔记（六）

一、对象导航查询

之前的客户和联系人的关系是一 对多的关系：一对多

场景：根据客户id查询客户，在查出该客户的所有联系人

 @Test
    public void selectTest(){
        SessionFactory sessionFactory = null;
        Session session = null;
        Transaction transaction = null;
        try{
            sessionFactory = HibernateUtils.getSessionFactory();
            session = sessionFactory.openSession();
            transaction = session.beginTransaction();
            //根据c_id 查询出该客户
            Customer customer = session.get(Customer.class,1);
            //然后查询出该客户联系人
            Set<Salesperson> set  = customer.getSalespersonSet();
            Iterator<Salesperson> it = set.iterator();
            while (it.hasNext()) {
                Salesperson str = it.next();
                System.out.println(str.getS_name());
            }
            transaction.commit();
        }catch (Exception e){
            transaction.rollback();
            e.printStackTrace();
        }finally{
            session.close();
            sessionFactory.close();
        }
    }

二、HQL查询

• 查询所有客户信息
  • 创建Query对象，写出hql语句
  • 调用query对象里面的方法得到结果
  • 查询所有 from+实体类名称

    @Test
    public void selectTest(){
        SessionFactory sessionFactory = null;
        Session session = null;
        Transaction transaction = null;
        try{
            sessionFactory = HibernateUtils.getSessionFactory();
            session = sessionFactory.openSession();
            transaction = session.beginTransaction();
            //创建query对象
              Query query =  session.createQuery("from Customer");

             //调用方法得到结果
            List<Customer> list = query.list();
            for (Customer customer: list) {
                System.out.println(customer.getC_id()+"-"+customer.getC_name());
            }
            transaction.commit();
        }catch (Exception e){
            transaction.rollback();
            e.printStackTrace();
        }finally{
            session.close();
            sessionFactory.close();
        }
    }

• 条件查询
  • 语句：from 实体类名称 where 实体类属性=？ and 实体类名称

@Test
    public void selectByCidAndCnameTest(){
        SessionFactory sessionFactory = null;
        Session session = null;
        Transaction transaction = null;
        try{
            sessionFactory = HibernateUtils.getSessionFactory();
            session = sessionFactory.openSession();
            transaction = session.beginTransaction();
            //创建query对象
            Query query =  session.createQuery("from Customer where c_id = ? and c_name = ?");
            query.setParameter(0,1);
            query.setParameter(1,"李客户");
            //调用方法得到结果
            List<Customer> list = query.list();
            for (Customer customer: list) {
                System.out.println(customer.getC_id()+"-"+customer.getC_name());
            }
            transaction.commit();
        }catch (Exception e){
            transaction.rollback();
            e.printStackTrace();
        }finally{
            session.close();
            sessionFactory.close();
        }
    }

条件查询

• 排序查询
  • 语句：from 实体类名称 order by 实体类名称 asc/desc

@Test
    public void selectOrderByTest(){
        SessionFactory sessionFactory = null;
        Session session = null;
        Transaction transaction = null;
        try{
            sessionFactory = HibernateUtils.getSessionFactory();
            session = sessionFactory.openSession();
            transaction = session.beginTransaction();
            //创建query对象
            Query query =  session.createQuery("from Customer order by  c_id desc ");
            //调用方法得到结果
            List<Customer> list = query.list();
            for (Customer customer: list) {
                System.out.println(customer.getC_id()+"-"+customer.getC_name());
            }
            transaction.commit();
        }catch (Exception e){
            transaction.rollback();
            e.printStackTrace();
        }finally{
            session.close();
            sessionFactory.close();
        }
    }

• 分页查询

 @Test
    public void selectLimitTest(){
        SessionFactory sessionFactory = null;
        Session session = null;
        Transaction transaction = null;
        try{
            sessionFactory = HibernateUtils.getSessionFactory();
            session = sessionFactory.openSession();
            transaction = session.beginTransaction();
            //创建query对象
            Query query =  session.createQuery("from Customer");
            //设置分页数据
            query.setFirstResult(0);
            query.setMaxResults(2);
            //调用方法得到结果
            List<Customer> list = query.list();
            for (Customer customer: list) {
                System.out.println(customer.getC_id()+"-"+customer.getC_name());
            }
            transaction.commit();
        }catch (Exception e){
            transaction.rollback();
            e.printStackTrace();
        }finally{
            session.close();
            sessionFactory.close();
        }
    }

• 投影查询
  • 语句：select * from 实体类属性名称一，实体类属性名称二， from 实体类名称
  • select 后面不能写 * 号，不支持

 @Test
    public void selectSomeTest(){
        SessionFactory sessionFactory = null;
        Session session = null;
        Transaction transaction = null;
        try{
            sessionFactory = HibernateUtils.getSessionFactory();
            session = sessionFactory.openSession();
            transaction = session.beginTransaction();
            //创建query对象
            Query query =  session.createQuery("select c_name from Customer");
            //调用方法得到结果
            List<Object> lists = query.list();
            for (Object list: lists) {
                System.out.println(list);
            }
            transaction.commit();
        }catch (Exception e){
            transaction.rollback();
            e.printStackTrace();
        }finally{
            session.close();
            sessionFactory.close();
        }
    }

image.png

• 聚集函数使用
  • count ，sum , avg , mac , min
  • 语句：select count(*) from 实体类名称

@Test
    public void selectHanshuTest(){
        SessionFactory sessionFactory = null;
        Session session = null;
        Transaction transaction = null;
        try{
            sessionFactory = HibernateUtils.getSessionFactory();
            session = sessionFactory.openSession();
            transaction = session.beginTransaction();
            //创建query对象
            Query query =  session.createQuery("select count(*) from Customer");
            //调用方法得到结果
            Object count = query.uniqueResult();
            //先转换成long类型，再转换为int
            Long co = Long.parseLong(count.toString());
            System.out.println(co.intValue());
            transaction.commit();
        }catch (Exception e){
            transaction.rollback();
            e.printStackTrace();
        }finally{
            session.close();
            sessionFactory.close();
        }
    }

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