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éå®'}]
[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éå®'}]}, 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éå®'}]}]
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