Criteria查询

最新推荐文章于 2021-02-16 02:51:03 发布

最新推荐文章于 2021-02-16 02:51:03 发布 · 348 阅读

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Hibernate的三种查询方式

1.HQL (Hibernate Query Lanuage) 语句，这是类似SQL语句的一种对象化查询语句.

2.使用Criteria对象，进行按条件查询(Query by Criteria，简称QBC)和按示例查询(Query by Example 简称QBE).

3.生成原生的sql(Native SQL)语句.

Criteria的基本使用

Transaction tx = session.beginTransaction();
Criteria criteria = session.createCriteria(Testbook.class);
List<Testbook> list=criteria.list();
tx.commit();

查询Testbook 中所有的数据，然后返回

Criteria 接口的核心方法

add()      增加一个代表查询条件的Criterion对象
addOrder()    增加一个代表排序的Criterion对象
createAlias()    创建关联查询，为所关联的持久化类建立别名
createCriteria()   在相互关联的持久化类之间建立条件约束
setFirstResult()   设定要获取的第一条记录的位置
setMaxResults()    设定要获取的记录的最大数量
list()     获取满足查询条件的记录的集合
uniqueResult()    获取满足查询条件的唯一记录

对查询结果进行排序

Transaction tx = session.beginTransaction();
Criteria criteria = session.createCriteria(Testbook.class).add(
Restrictions.like("name","任%")).add(Restrictions.between("id",1000,1010));
criteria.addOrder(Order.desc("id")).addOrder(Order.asc("createdTime"));
List<Testbook> list=criteria.list();
tx.commit();

实现分页显示数据

Transaction tx = session.beginTransaction();
Criteria criteria = session.createCriteria(Testbook.class).add(
Restrictions.like("name","任%"));
criteria.addOrder(Order.desc("id"));
criteria.setMaxResults(30);
criteria.setFirstResult(10);//setFirstResult()从0开始计数
List<Testbook> list=criteria.list();
tx.commit();

只查询一条记录

Transaction tx = session.beginTransaction();
Criteria criteria = session.createCriteria(Testbook.class).add(
Restrictions.like("name","任%"));
criteria.addOrder(Order.desc("id"));
criteria.setMaxResults(1);
Testbook tb=(Testbook)criteria.uniqueResult();
tx.commit();

Restrictions类

<----------------------------------------------------------------------------------------------------------->

条件"或"方式组合查询条件

Transaction tx = session.beginTransaction();
Criteria criteria=session.createCriteria(Testbook.class);
Criterion criterion1=Restrictions.or(Restrictions.like("name","任%"),
Restrictions.between("id",1000,1010));
criteria.add(criterion1);
List<Testbook> list=criteria.list();
tx.commit();

使用原生SQL语句设定查询条件

Transaction tx = session.beginTransaction();
Criteria criteria=session.createCriteria(Testbook.class);
criteria.add(Restrictions.sqlRestriction("{alias}.name=?","Narcissus",Hibernate.STRING));
List<Testbook> list=criteria.list();
tx.commit()

统计函数查询

Transaction tx = session.beginTransaction();
Criteria criteria=session.createCriteria(Testbook.class);
criteria.setProjection(Projections.max("price"));
Double maxValue=(Double)criteria.uniqueResult();
tx.commit();
System.out.println(maxValue);

统计函数组合查询条件

Transaction tx = session.beginTransaction();
Criteria criteria=session.createCriteria(Testbook.class);
criteria.setProjection(Projections.max("price"));
Double maxValue=(Double)criteria.uniqueResult();
tx.commit();
System.out.println(maxValue);

获取多个统计函数的值

Transaction tx = session.beginTransaction();
Criteria criteria=session.createCriteria(Testbook.class);
ProjectionList proList=Projections.projectionList();
proList.add(Projections.max("price"));
proList.add(Projections.min("price"));
proList.add(Projections.avg("price"));
proList.add(Projections.sum("price"));
proList.add(Projections.count("price"));
proList.add(Projections.countDistinct("price"));
proList.add(Projections.rowCount());
criteria.setProjection(proList);
Object values[]=(Object[])criteria.uniqueResult();
tx.commit();

分组查询

Transaction tx = session.beginTransaction();
Criteria criteria=session.createCriteria(Testbook.class);
criteria.setProjection(Projections.groupProperty("price"));
List<Double> list=criteria.list();
tx.commit();

分组统计

Transaction tx = session.beginTransaction();
Criteria criteria=session.createCriteria(Testbook.class);
ProjectionList proList=Projections.projectionList();
proList.add(Projections.rowCount());//商品的个数
proList.add(Projections.sum("price"));
proList.add(Projections.groupProperty("name"));
criteria.setProjection(proList);
List<Double> list=criteria.list();
tx.commit();

投影查询
在一个表中有很多个字段，投影查询只是查询某一个或多个字段，也称局部查询

Transaction tx = session.beginTransaction();
Criteria criteria=session.createCriteria(Testbook.class);
criteria.setProjection(Property.forName("price"));
criteria.add(Restrictions.gt("price",new Double(40.0)))
List<Double> list=criteria.list();
tx.commit();

使用Property类的forName()方法实现分组统计

Transaction tx = session.beginTransaction();
Criteria criteria=session.createCriteria(Testbook.class);
ProjectionList proList=Projections.projectionList();
proList.add(Projections.forName("price").max());
proList.add(Projections.forName("price").min());
proList.add(Projections.forName("price").avg());
proList.add(Projections.forName("category.id").group().as("c"));
criteria.setProjection(proList);
criteria.addOrder(Order.desc("c"));
List<Object[]> list=criteria.list();
tx.commit();

使用DetachedCriteria对象实现离线查询

//在表现层，构造DetachedCriteria对象，保存用户动态的查询条件
DetachedCriteria detchedCriteria=DetachedCriteria.forClass(Testbook.class);
detchedCriteria.add(Restrictions.like("name","任%")).add(Restrictions.between("id",new Integer(1),new Integer(10)));
detchedCriteria.addOrder(Order.desc("id"));

//在业务逻辑层，DetachedCriteria对象与当前的Session对象进行绑定，获取查询结果
Session session=HibernateSessionFactoryUtil.getSessionFactory().getCurrentSession();
Transaction tx=detchedCriteria.getExecutableCriteria(session);
List<Testbook> list=criteria.list();
tx.commit();

根据示例对象进行查询

先定义一个模板然后把这个模板的样式传进去，查询，例如这里定义的Testbook中的名字为Narcissus的字段，进行查询，条件可以为一个也可以为多个，对应的就是where中的条件

Testbook tb=new Testbook();
tb.setName("Narcissus");
Session session=HibernateSessionFactoryUtil.getSessionFactory().getCurrentSession();
Transaction tx = session.beginTransaction();
Criteria criteria=session.createCriteria(Testbook.class);
Criteria.add(Example.creaate(tb));
List<Testbook> list=criteria.list();
tx.commit();