浅谈Hibernate--Hibernate查询(Query Language) (转)

1.查询对象：Query有org.hibernate.query和javax.persistence.query,用法如下

如果按条件查找
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2.占位符：比如下面的例子：min 和：max,和query.setParameter(key,value);

链式的也可以，同时这里setParameter("","")是会自动设置参数的值，如果知道传入的类型可以setInteger..
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3.分页效果：
通过query.setMaxResult(n).setFirstResult(m)取出m~n之间的记录
setFirstResult(m):选择从第几行开始取，默认是row0
setMaxResult(n):决定取出多少条记录，默认是往后所有rows
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和下面普通的ql语句实现一样
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4.获取子属性
Query query=session.createQuery("from Score s where s.xxx.id=..")
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同时也可以把临时对象取出来放到Object或者自己建立的辅助类里去
1.Query query=session.createQuery("select s.name,c.name from Student s,Course c where s.id=.. and c.id=..")
2.Query query=session.createQuery("select new VObj(s.name,c.name) from Student s,Course c where s.id=.. and c.id=..")
取出部分属性封装成一个新的对象是不可取的，最好完整的取出整个属性以保证他逻辑的关联性；
如果要取出就这样取
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5.单个对象匹配
如果你知道取出的是唯一的一个对象，那么就不用query.list(),要用query.uniqueResult();效率比较高
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count(*)返回的是一个long类型
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in
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Group by
select avg(s.age) from Student group by s.col;
having
select count(*)  from Student s where group by s.col having count(*)>3;
空值Empty：下面是学生类(Student)中有Set<Course> courses属性(学生所选课程) 选出哪些选课为空的学生
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Like: %多个 ; _ 一个
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distinct
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6.可以把QL语句放在一起，以便维护修改用@NamedQueries和@NamedQuery，调用的时候用session.getNamedQuery(QueryName)
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7.使用数据库自身语言
如果用hql解决不了问题，那就用sql语言来解决，通过createSQLQuery()来搜索表，并用addEntity(xx.Class)转换成对象
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当然这也可以用命名的Query
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8.批量删除：通过query.executeQuery();return一个int类型，返回update和delete成功的行数
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原文：http://www.cnblogs.com/cornucopia/p/4540120.html