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1、HQL 查询及语法HQL:Hibernate Query LanguageHQL 是完全面向对象的查询语言，因此可以支持继承和多态等特征。HQL 查询依赖于 Query 类，每个 Query 实例对应一个查询对象，使用 HQL 查询按如下步骤进行：(1)获取 Hibernate Session 对象；(2)编写 HQL 语句；(3)以 HQL 语句作为参数，调用 Session 的 createQuery 方法创建查询对象；(4)如果 HQL 语句包含参数，调用 Query 的 setXxx 方法为参数赋值；(5)调用 Query 对象的 list 等方法遍历查询结果。查询示例：public
2、class HqlQuerypublic static void main(String args) throws Exception HqlQuery mgr = new HqlQuery();/调用查询方法mgr.findPersons();/调用第二个查询方法mgr.findPersonByHappenDate();HibernateUtil.sessionFactory.close();/第一个查询方法private void findPersons() /获得 Hibernate SessionSession sess = HibernateUtil.currentSession()
3、;/开始事务Transaction tx = sess.beginTransaction();/以 HQL 语句创建 Query 对象/执行 setString 方法为 HQL 语句的参数赋值/Query 调用 list 方法访问查询的全部实例List p1 = sess.createQuery(“from Person p where o.myEvents.title = :eventTitle“).setString(“eventTitle“, “很普通事情“).list();/遍历查询的全部结果for (Iterator pit = p1.iterator(); pit.haxNext(
4、); )Person p = (Person)pit.next();System.out.println(p.getName();/提交事务mit();HibernateUtil.closeSession();/第二个查询方法private void findPersonByHappenDate() throws Exception Session sess = HibernateUtil.currentSession();Transaction tx = sess.beginTransaction();/解析出 Date 对象SimpleDateFormat sdf = new Simple
5、DateFormat(“yyyy-MM-dd“);Date start = sdf.parse(“2007-11-27“);System.out.println(“系统开始通过日期查找人“ + start);/通过 Session 的 createQuery 方法创建 Query 对象/设置参数/返回结果集List pl = sess.createQuery(“from Person p where p.myEvents.happenDate between :firstDateand :endDate“).setDate(“firstDate“, start).setDate(“endDat
6、e“, new Date().list();/遍历结果集for (Iterator pit = pl.iterator(); pit.hasNext(); )Person p = (Person)pit.next();System.out.println(p.getName();mit();HibernateUtil.closeSession();$下面介绍 HQL 语句的语法1.from 子句from Person表明从 Person 持久化类中选出全部的实例。推荐：from Person as p2.select 子句select p.name from Person as pselect
7、 p.name.firstName from Person as pselect new list(p.name, p.address) from Person as pselect new ClassTest(p.name, p.address) from Person as p (有前提)select p.name as personName from Person as pselect new map(p.name as personName) from Person as p (与 new map()结合更普遍)3.聚集函数avg,count,max,min,sumselect cou
8、nt(*) from Personselect max(p.age) from Person as pselect p.name | “ | p.address from Person as p4.多态查询from Person as pfrom java.lang.Object ofrom Named as n5.where 子句from Person where name like “tom%“from Person as p where p.name like “tom%“from Cat cat where cat.mate.name like “kit%“select * from
9、cat_table as table1 cat_table as table2 where table1.mate =table2.id and table1.name like “kit%“from Foo foo where foo.bar.baz.customer.address.city like “fuzhou%“from Cat cat, Cat rival where cat.mate = rival.mateselect cat, matefrom Cat cat, Cat matewhere cat.mate = matefrom Cat as cat where cat.i
10、d = 123from Cat as cat where cat.mate.id = 69from Person as personwhere person.id.country = AUand person.id.medicareNumber = 123456from Account as accountwhere account.owner.id.country = AUand account.owner.id.medicareNumber = 123456from Cat cat where cat.class = DomesticCatfrom Account as a where a
11、.person.name.firstName like “dd%“ / 正确from Account as a where a.person.name like “dd%“ / 错误6.表达式from DomesticCat cat where cat.name between A and Bfrom DomesticCat cat where cat.name in (Foo, Bar, Baz)from DomesticCat cat where cat.name not between A and Bfrom DomesticCat cat where cat.name not in (
12、Foo, Bar, Baz)from DomesticCat cat where cat.name is nullfrom Person as p where p.address is not nulltrue 1, false 0from Cat cat where cat.alive = truefrom Cat cat where cat.kittens.size 0from Cat cat where size(cat.kittens) 0from Calendar cal where maxelement(cal.holidays) current datefrom Order or
13、der where maxindex(order.items) 100from Order order where minelement(order.items) 10000/操作集合元素select mother from Cat as mother, Cat as kitwhere kit in elements(foo.kittens)/p 的 name 属性等于集合中某个元素的 name 属性select p from NameList list, Person pwhere p.name = some elements(list.names)/操作集合元素from Cat cat w
14、here exists elements(cat.kittens)from Player p where 3 all elements(p.scores)from Show show where fizard in indices(show.acts)/items 是有序集合属性，items0代表第一个元素from Order order where order.items0.id = 1234/holidays 是 map 集合属性，holidaysnational day是代表其中第一个元素select person from Person person, Calendar calenda
15、rwhere calendar.holidaysnational day = person.birthDayand person.nationality.calendar = calendar/下面同时使用 list 集合和 map 集合属性select item from Item item, Order orderwhere order.itemsorder.deliveredItemIndices0 = item and order.id = 11select item from Item item, Order orderwhere order.itemsmaxindex(order.
16、items) = item and order.id = 11select item from Item item, Order orderwhere order.itemssize(order.items) - 1 = itemselect custfrom Product prod,Store storeinner join store.customers custwhere prod.name = widgetand store.location.name in Melbourne, Sydneyand prod = all elements(cust.currentOrder.lineItems)SELECT cust.name, cust.address, cust.phone, cust.id, cust.current_orderFRO
