Hibernate学习笔记（第四天）

Hibernate_day04

1.今日任务

·Hibernate查询-HQL语法

·Hibernate查询-Criteria语法

·Hibernate查询优化

·Crm案例练习：为客户列表增加查询条件

2.相关知识

2.1Hibernate查询-HQL语法

2.1.1基本语法

public class TestHql {// 基本语法@Testpublic void fun1() {Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------String hql = " from  cn.itcast.domain.Customer ";// 完整写法String hql2 = " from  Customer "; // 简单写法String hql3 = " from java.lang.Object ";Query query = session.createQuery(hql3);List list = query.list();System.out.println(list);// ----------------------------------------------------tx.commit();session.close();}@Test// 排序public void fun2() {Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------String hql1 = " from  cn.itcast.domain.Customer order by cust_id asc ";// 完整写法String hql2 = " from  cn.itcast.domain.Customer order by cust_id desc ";// 完整写法Query query = session.createQuery(hql2);List list = query.list();System.out.println(list);// ----------------------------------------------------tx.commit();session.close();}@Test// 条件查询public void fun3() {Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------String hql1 = " from  cn.itcast.domain.Customer where cust_id =? ";// 完整写法String hql2 = " from  cn.itcast.domain.Customer where cust_id = :id ";// 完整写法Query query = session.createQuery(hql2);// query.setParameter(0, 2l);query.setParameter("id", 2l);List list = query.list();System.out.println(list);// ----------------------------------------------------tx.commit();session.close();}@Test// 分页查询public void fun4() {Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------String hql1 = " from  cn.itcast.domain.Customer  ";// 完整写法Query query = session.createQuery(hql1);// limit ?,?// (当前页数-1)*每页条数query.setFirstResult(2);query.setMaxResults(2);List list = query.list();System.out.println(list);// ----------------------------------------------------tx.commit();session.close();}@Test// 统计查询// count 计数// sum 求和// avg 平均数// max// minpublic void fun5() {Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------String hql1 = " select count(*) from  cn.itcast.domain.Customer  ";// 完整写法String hql2 = " select sum(cust_id) from  cn.itcast.domain.Customer  ";// 完整写法String hql3 = " select avg(cust_id) from  cn.itcast.domain.Customer  ";// 完整写法String hql4 = " select max(cust_id) from  cn.itcast.domain.Customer  ";// 完整写法String hql5 = " select min(cust_id) from  cn.itcast.domain.Customer  ";// 完整写法Query query = session.createQuery(hql5);Number number = (Number) query.uniqueResult();System.out.println(number);// ----------------------------------------------------tx.commit();session.close();}@Test// 投影查询public void fun6() {Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------String hql1 = " select cust_name from  cn.itcast.domain.Customer  ";String hql2 = " select cust_name,cust_id from  cn.itcast.domain.Customer  ";String hql3 = " select new Customer(cust_id,cust_name) from  cn.itcast.domain.Customer  ";Query query = session.createQuery(hql3);List list = query.list();System.out.println(list);// ----------------------------------------------------tx.commit();session.close();}}

 

2.1.2多表查询语法

 

//学习HQL语法(不常用) - 多表查询语法public class TestHql2 {// 回顾-原生SQL// 交叉连接-笛卡尔积(避免)// select * from A,B// 内连接// |-隐式内连接// select * from A,B where b.aid = a.id// |-显式内连接// 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// 内连接(迫切)// 外连接// |-左外(迫切)// |-右外(迫切)@Test// HQL 内连接 => 将连接的两端对象分别返回.放到数组中.public void fun1() {Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------String hql = " from Customer c inner join c.linkMens ";Query query = session.createQuery(hql);List<Object[]> list = query.list();for (Object[] arr : list) {System.out.println(Arrays.toString(arr));}// ----------------------------------------------------tx.commit();session.close();}@Test// HQL 迫切内连接 => 帮我们进行封装.返回值就是一个对象public void fun2() {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> list = query.list();System.out.println(list);// ----------------------------------------------------tx.commit();session.close();}@Test// HQL 左外连接 => 将连接的两端对象分别返回.放到数组中.public void fun3() {Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------String hql = " from Customer c left join c.linkMens ";Query query = session.createQuery(hql);List<Object[]> list = query.list();for (Object[] arr : list) {System.out.println(Arrays.toString(arr));}// ----------------------------------------------------tx.commit();session.close();}@Test// HQL 右外连接 => 将连接的两端对象分别返回.放到数组中.public void fun4() {Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------String hql = " from Customer c right join c.linkMens ";Query query = session.createQuery(hql);List<Object[]> list = query.list();for (Object[] arr : list) {System.out.println(Arrays.toString(arr));}// ----------------------------------------------------tx.commit();session.close();}}

 

 

2.2Hibernate查询-Criteria语法

2.2.1基本语法

public class TestCriteria {@Test// 基本语法public void fun1() {Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------Criteria c = session.createCriteria(Customer.class);List<Customer> list = c.list();System.out.println(list);// ----------------------------------------------------tx.commit();session.close();}@Test// 条件语法public void fun2() {Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------Criteria c = session.createCriteria(Customer.class);// c.add(Restrictions.idEq(2l));c.add(Restrictions.eq("cust_id", 2l));List<Customer> list = c.list();System.out.println(list);// ----------------------------------------------------tx.commit();session.close();}@Test// 分页语法 - 与HQL一样public void fun3() {Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------Criteria c = session.createCriteria(Customer.class);// limit ?,?c.setFirstResult(0);c.setMaxResults(2);List<Customer> list = c.list();System.out.println(list);// ----------------------------------------------------tx.commit();session.close();}@Test// 排序语法public void fun4() {Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------Criteria c = session.createCriteria(Customer.class);c.addOrder(Order.asc("cust_id"));// c.addOrder(Order.desc("cust_id"));List<Customer> list = c.list();System.out.println(list);// ----------------------------------------------------tx.commit();session.close();}@Test// 统计语法public void fun5() {Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// ----------------------------------------------------Criteria c = session.createCriteria(Customer.class);// 设置查询目标c.setProjection(Projections.rowCount());List list = c.list();System.out.println(list);// ----------------------------------------------------tx.commit();session.close();}}

 

 

2.2.2 离线Criteria

/* * 离线Criteria */public class TestCriteria2 {@Testpublic void fun1(){//Service/web层DetachedCriteria dc  = DetachedCriteria.forClass(Customer.class);dc.add(Restrictions.idEq(6l));//拼装条件(全部与普通Criteria一致)//----------------------------------------------------Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();//----------------------------------------------------Criteria c = dc.getExecutableCriteria(session);List list = c.list();System.out.println(list);//----------------------------------------------------tx.commit();session.close();}}

 

2.3Hibernate查询优化

2.3.1 类级别查询

//懒加载|延迟加载public class TestLazy {@Test// get方法 : 立即加载.执行方法时立即发送sql语句查询结果public void fun1(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();//----------------------------------------------------Customer c = session.get(Customer.class, 2l);System.out.println(c);//----------------------------------------------------tx.commit();session.close();}@Test// load方法(默认):是在执行时,不发送任何sql语句.返回一个对象.使用该对象时,才执行查询.// 延迟加载: 仅仅获得没有使用.不会查询.在使用时才进行查询.// 是否对类进行延迟加载: 可以通过在class元素上配置lazy属性来控制.//lazy:true  加载时,不查询.使用时才查询b//lazy:false 加载时立即查询.public void fun2(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();//----------------------------------------------------Customer c = session.load(Customer.class, 2l);//----------------------------------------------------tx.commit();session.close();System.out.println(c);}}

 

lazy(默认值):true, 查询类时,会返回代理对象.会在使用属性时,根据关联的session查询数据库.加载数据.

lazy:false.load方法会与get方法没有任何区别.调用时即加载数据.

结论:为了提高效率.建议使用延迟加载(懒加载)

注意:使用懒加载时要确保,调用属性加载数据时,session还是打开的.不然会抛出No Session异常

 

2.3.2 关联级别查询

Customer.hbm.xml

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-mapping PUBLIC     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.itheima.domain" ><class name="Customer" table="cst_customer" lazy="false" ><id name="cust_id"  ><generator class="native"></generator></id><property name="cust_name" column="cust_name" ></property><property name="cust_source" column="cust_source" ></property><property name="cust_industry" column="cust_industry" ></property><property name="cust_level" column="cust_level" ></property><property name="cust_linkman" column="cust_linkman" ></property><property name="cust_phone" column="cust_phone" ></property><property name="cust_mobile" column="cust_mobile" ></property><!-- lazy属性: 决定是否延迟加载true(默认值): 延迟加载,懒加载false: 立即加载extra: 极其懒惰fetch属性: 决定加载策略.使用什么类型的sql语句加载集合数据select(默认值): 单表查询加载join: 使用多表查询加载集合subselect:使用子查询加载集合 --> <!-- batch-size: 抓取集合的数量为3. 抓取客户的集合时,一次抓取几个客户的联系人集合.  --><set name="linkMens" batch-size="3"  ><key column="lkm_cust_id" ></key><one-to-many class="LinkMan" /></set></class></hibernate-mapping>

 

LinkMan.hbm.xml

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-mapping PUBLIC     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping package="cn.itcast.domain" ><class name="LinkMan" table="cst_linkman" ><id name="lkm_id"  ><generator class="native"></generator></id><property name="lkm_gender"  ></property><property name="lkm_name"  ></property><property name="lkm_phone"  ></property><property name="lkm_email"  ></property><property name="lkm_qq"  ></property><property name="lkm_mobile"  ></property><property name="lkm_memo"  ></property><property name="lkm_position"  ></property><!-- fetch 决定加载的sql语句select: 使用单表查询join : 多表查询lazy  决定加载时机false: 立即加载proxy: 由customer的类级别加载策略决定. --><many-to-one name="customer" column="lkm_cust_id" class="Customer" fetch="join" lazy="proxy"  ></many-to-one></class></hibernate-mapping>

 

测试代码：

//关联级别 延迟加载 & 抓取策略public class TestLazyFetch {@Test//fetch:select单表查询//lazy:proxy  //customer-true 懒加载public void fun1(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();//----------------------------------------------------LinkMan lm = session.get(LinkMan.class, 3l);Customer customer = lm.getCustomer();System.out.println(customer);//----------------------------------------------------tx.commit();session.close();}@Test//fetch:join多表//lazy: 失效  public void fun3(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();//----------------------------------------------------LinkMan lm = session.get(LinkMan.class, 3l);Customer customer = lm.getCustomer();System.out.println(customer);//----------------------------------------------------tx.commit();session.close();}@Test//fetch:select单表查询//lazy:proxy  //customer-false 立即加载public void fun2(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();//----------------------------------------------------LinkMan lm = session.get(LinkMan.class, 3l);Customer customer = lm.getCustomer();System.out.println(customer);//----------------------------------------------------tx.commit();session.close();}}

 

结论:为了提高效率.fetch的选择上应选择select. lazy的取值应选择 true. 全部使用默认值.

no-session问题解决: 扩大session的作用范围.

2.3.3批量抓取

<!-- batch-size: 抓取集合的数量为3. 抓取客户的集合时,一次抓取几个客户的联系人集合.  --><set name="linkMens" batch-size="3"  ><key column="lkm_cust_id" ></key><one-to-many class="LinkMan" /></set>

 

3.crm练习案例

练习:为客户列表增加查询条件

Servlet层方法：

public String list(HttpServletRequest request, HttpServletResponse response) throws Exception{DetachedCriteria dc = DetachedCriteria.forClass(Customer.class);//获取当期页int currentPage = 1;//如果参数为空 默认显示第一页if (request.getParameter("currentPage")!=null && !request.getParameter("currentPage").equals("")) {currentPage = Integer.parseInt(request.getParameter("currentPage"));}//获取筛选客户名称String cust_name = request.getParameter("cust_name");if (cust_name!=null) {//如果筛选客户名称不为空添加模糊查询条件dc.add(Restrictions.like("cust_name", "%"+cust_name+"%"));}//设置每一页显示几条记录int pageSize = 10;//调用业务层获取客户列表PageBean<Customer> pb = customerService.getCustomerByPage(dc,currentPage,pageSize);request.setAttribute("pb", pb);return "/jsp/customer/list.jsp";}

 

Service层方法：

public PageBean<Customer> getCustomerByPage(DetachedCriteria dc, int currentPage, int pageSize) throws Exception {// 获取客户列表List<Customer> list = customrDao.getCustomerListByPage(dc,currentPage,pageSize);// 获取总数量int count = customrDao.getCount();// 封装到pagebeanPageBean<Customer> pb = new PageBean<>(list, currentPage, pageSize, count);return pb;}

 

Dao层方法：

public List<Customer> getCustomerListByPage(DetachedCriteria dc, int currentPage, int pageSize) {// TODO Auto-generated method stub// 打开会话Session session = HibernateUtils.openSession();Criteria criteria = null;//判断 dc是否为空if (dc==null) {criteria = session.createCriteria(Customer.class);}else{//将dc转换为criteriacriteria = dc.getExecutableCriteria(session);}// 设置分页参数criteria.setFirstResult((currentPage-1)*pageSize);criteria.setMaxResults(pageSize);// 获取客户列表List<Customer> list = criteria.list();// 关闭sessionsession.close();return list;}