• HIbernate——hibernate中的各种查询


    一、通过oid查询

    @Test
    public void func1(){
    
        Session session = HibernateUtils.openSession();
    
        Transaction tx = session.beginTransaction();
    
        // ----------------------------------------
    
        Customer cs = session.get/load(Customer.class, 1L);  // load是,等到用的时候才知晓
    
        System.out.println(cs);
    
        // ----------------------------------------
    
            tx.commit();
            session.close();
    }
    

    二、HQL查询

    1、基本查询

    @Test
    public void func1(){
    
        Session session = HibernateUtils.openSession();
    
        Transaction tx = session.beginTransaction();
    
        // ----------------------------------------
    
        String hql = "from Customer";
    
        Query query = session.createQuery(hql);
    
        List<Customer> list = query.list();      // 获取所有数据
        //Customer cs = (Customer) query.uniqueResult();  // 获取单条数据(只有一条才能使用)
    
        System.out.println(list);
    
        // ----------------------------------------
    
            tx.commit();
            session.close();
    }
    

    2、条件查询

    @Test
    public void func1(){
    
        Session session = HibernateUtils.openSession();
    
        Transaction tx = session.beginTransaction();
    
        // ----------------------------------------
    
        String hql1 = "from Customer where cust_id=?";      // ?占位符
        String hql2 = "from Customer where cust_id=:id";    // 命名占位符
    
        Query query = session.createQuery(hql2);
    
        // query.setParameter(0,2L);
        query.setParameter("id",2L);
    
        // List<Customer> list = query.list();      // 获取所有数据
        Customer cs = (Customer) query.uniqueResult();  // 获取单条数据(只有一条才能使用)
    
        System.out.println(cs);
    
        // ----------------------------------------
    
            tx.commit();
            session.close();
    }
    

    3、排序

    @Test
    public void func1(){
    
        Session session = HibernateUtils.openSession();
    
        Transaction tx = session.beginTransaction();
    
        // ----------------------------------------
    
        String hql1 = "from Customer order by cust_id asc";      // 正序排
        String hql2 = "from Customer order by cust_id desc";      // 逆序排
    
        Query query = session.createQuery(hql1);
    
        List<Customer> list = query.list();
    
        System.out.println(list);
    
    
        // ----------------------------------------
    
            tx.commit();
            session.close();
    }
    

    4、分页查询

    @Test
    public void func1(){
    
        Session session = HibernateUtils.openSession();
    
        Transaction tx = session.beginTransaction();
    
        // ----------------------------------------
    
        String hql = "from Customer";
    
        Query query = session.createQuery(hql);
    
        query.setFirstResult(1);
        query.setMaxResults(3);
    
        List<Customer> li = query.list();
    
        System.out.println(li);
    
    
        // ----------------------------------------
    
            tx.commit();
            session.close();
    }
    

    5、聚合查询

    @Test
    public void func1(){
    
        Session session = HibernateUtils.openSession();
    
        Transaction tx = session.beginTransaction();
    
        // ----------------------------------------
    
        String hql1 = "select count (*) from Customer ";        // 返回影响数(row)
        String hql2 = "select max (cust_id) from Customer ";    // 最大值
        String hql3 = "select min (cust_id) from Customer ";    // 最小值
        String hql4 = "select avg (cust_id) from Customer ";    // 平均值
        String hql5 = "select sum (cust_id) from Customer ";    // 求和
    
        Query query = session.createQuery(hql4);
    
        Number num = (Number) query.uniqueResult();
    
        System.out.println(num);
    
    
        // ----------------------------------------
    
            tx.commit();
            session.close();
    }
    

    6、投影查询

    @Test
    public void func1(){
    
        Session session = HibernateUtils.openSession();
    
        Transaction tx = session.beginTransaction();
    
        // ----------------------------------------
    
        String hql = "select cust_id,cust_name from Customer ";
    
        Query query = session.createQuery(hql);
    
        List li = query.list();
    
        System.out.println(li);
    
    
        // ----------------------------------------
    
            tx.commit();
            session.close();
    }
    

    7、多表查询

    SQL的多表查询

    交叉连接-笛卡尔积(最好不要用,会查出重复数据)
    
    内连接
      |-隐式内连接
    		select * from A,B where b.aid=a.id
      |-显示内连接
    		select * from A inner join B on b.aid=a.id
    		
    外连接
      |-左外
    		select * from A left [outer] join B on b.aid=a.id
      |-右外
    		select * from A right [outer] join B on b.aid=a.id

    HQL的多表查询(一般不用,还不如用原生SQL呢)

    1、内连接

    @Test
    public void func1(){
    
        Session session = HibernateUtils.openSession();
    
        Transaction tx = session.beginTransaction();
    
        // ----------------------------------------
    
        String hql = "from Customer c inner join c.linkMens";
    
        Query query = session.createQuery(hql);
    
        List<Object[]> li = query.list();
    
        for(Object[] o : li){
    
            System.out.println(Arrays.toString(o));
        }
    
    
        // ----------------------------------------
    
            tx.commit();
            session.close();
    }
    

    [Customer [cust_id=1, cust_name=鑫哥论文], LinkMan{lkm_id=5, lkm_name='tom'}]
    [Customer [cust_id=1, cust_name=鑫哥论文], LinkMan{lkm_id=6, lkm_name='计震宇'}]
    [Customer [cust_id=1, cust_name=鑫哥论文], LinkMan{lkm_id=7, lkm_name='计震宇'}]

    2、内连接迫切

    查询语句上多了个fetch,返回的是Customer对象

    public void func1(){
    
        Session session = HibernateUtils.openSession();
    
        Transaction tx = session.beginTransaction();
    
        // ----------------------------------------
    
        String hql = "from Customer c inner join fetch c.linkMens";
    
        Query query = session.createQuery(hql);
    
        List<Customer> li = query.list();
    
        System.out.println(li);
    
        // ----------------------------------------
    
            tx.commit();
            session.close();
    }
    

    [Customer{cust_id=1, cust_name='百度公司', linkMens=[LinkMan{lkm_id=1, lkm_name='于佳鑫'}, LinkMan{lkm_id=6, lkm_name='计震宇'}]}, Customer{cust_id=2, cust_name='谷歌公司', linkMens=[LinkMan{lkm_id=3, lkm_name='张宝岩'}]}, Customer{cust_id=3, cust_name='360', linkMens=[LinkMan{lkm_id=4, lkm_name='tom'}]}, Customer{cust_id=4, cust_name='快播', linkMens=[LinkMan{lkm_id=5, lkm_name='tom'}]}, Customer{cust_id=1, cust_name='百度公司', linkMens=[LinkMan{lkm_id=1, lkm_name='于佳鑫'}, LinkMan{lkm_id=6, lkm_name='计震宇'}]}]

    3、左/右 外连接(迫切)

    @Test
    public void func1(){
    
        Session session = HibernateUtils.openSession();
    
        Transaction tx = session.beginTransaction();
    
        // ----------------------------------------
    
        String hql = "from Customer c left join c.linkMens";
    
        Query query = session.createQuery(hql);
    
        List<Object []> li = query.list();
    
        for (Object [] o : li){
    
            System.out.println(Arrays.toString(o));
        }
    
    
    
        // ----------------------------------------
    
            tx.commit();
            session.close();
    }

    三、Criteria查询

    1、基本查询

    public void func1(){
    
        Session session = HibernateUtils.openSession();
    
        Transaction tx = session.beginTransaction();
    
        // ----------------------------------------
    
        Criteria criteria = session.createCriteria(Customer.class);
    
        List list = criteria.list();
    
        System.out.println(list);
    
        // ----------------------------------------
    
            tx.commit();
            session.close();
    }
    

    2、条件查询

    public void func1(){
    
        Session session = HibernateUtils.openSession();
    
        Transaction tx = session.beginTransaction();
    
        // ----------------------------------------
    
        Criteria criteria = session.createCriteria(Customer.class);
    
        criteria.add(Restrictions.eq("cust_id",2L));     // 添加查询条件
    
        //List list = criteria.list();
        Customer result = (Customer) criteria.uniqueResult();
    
        System.out.println(result);
    
        // ----------------------------------------
    
            tx.commit();
            session.close();
    }
    

    3、分页查询

    public void func1(){
    
        Session session = HibernateUtils.openSession();
    
        Transaction tx = session.beginTransaction();
    
        // ----------------------------------------
    
        Criteria criteria = session.createCriteria(Customer.class);
    
        criteria.setFirstResult(2);
        criteria.setMaxResults(3);
    
        List<Customer> list = criteria.list();
    
        System.out.println(list);
    
        // ----------------------------------------
    
            tx.commit();
            session.close();
    }
    

    4、排序

    public void func1(){
    
        Session session = HibernateUtils.openSession();
    
        Transaction tx = session.beginTransaction();
    
        // ----------------------------------------
    
        Criteria criteria = session.createCriteria(Customer.class);
    
        criteria.addOrder(Order.asc("cust_id"));    // 正序
        criteria.addOrder(Order.desc("cust_id"));   // 逆序
    
        List<Customer> list = criteria.list();
    
        System.out.println(list);
    
        // ----------------------------------------
    
            tx.commit();
            session.close();
    }
    

    5、聚合运算

    public void func1(){
    
        Session session = HibernateUtils.openSession();
    
        Transaction tx = session.beginTransaction();
    
        // ----------------------------------------
    
        Criteria criteria = session.createCriteria(Customer.class);
    
        criteria.setProjection(Projections.rowCount());     // 查询总和
    
        Number num = (Number) criteria.uniqueResult();
    
        System.out.println(num);
    
        // ----------------------------------------
    
            tx.commit();
            session.close();
    }
    

    离线查询

    非离线

    离线(dao层可以不用变,我们在前面构造好查询条件就行了)

    代码实现

     

    四、查询优化

    load方法,当使用时,才进行SQL查询

    实际上,load方法是将Customer对象变成超级Customer对象,可以查询数据库,当调用后(查询数据库后),变成了普通的Customer对象

    public void func1(){
    
        Session session = HibernateUtils.openSession();
    
        Transaction tx = session.beginTransaction();
    
        // ----------------------------------------
    
        Customer load = session.load(Customer.class, 2L);
    
        System.out.println(load);
    
        // ----------------------------------------
    
            tx.commit();
            session.close();
    }
    

    它实际上也是依赖session的,所以session.close()后,就会报错

    所以我们可以使用 filter 来解决

    动态代理:(打印对象时有$就是代理对象)

    给对象搞代理的目的:对方法改造或增强

    连接池:
    目的:改变连接对象的关闭方法(不能让连接真的关闭 应该放回连接池),对connection进行代理

    解决中文乱码:
    对request对象进行代理,改造getParameterMap()...方法,变成没有乱码的

    类级别 延迟加载:
    将Customer对象变成超级Customer对象,可以查询数据库

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  • 原文地址:https://www.cnblogs.com/x54256/p/8470045.html
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