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

 

转载于:https://www.cnblogs.com/x54256/p/8470045.html

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