一、通过oid查询
@Testpublic 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
@Testpublic 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
@Testpublic 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
@Testpublic 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
@Testpublic 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
@Testpublic 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
@Testpublic 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
@Testpublic 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=‘è??é?????‘}]
[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=‘è??é?????‘}]}, 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=‘è??é?????‘}]}]
3、左/右 外连接（迫切）
@Testpublic 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
HIbernate——hibernate中的各种查询
原文地址：https://www.cnblogs.com/x54256/p/8470045.html