hibernate单表查询总结（下）

待我称王封你为后i 2023-10-17 11:31 16阅读 0赞

hibernate单表查询总结（下）  
**本博客接着[hibernate单表查询总结（上）][hibernate]继续就Hibernate的单表查询进行总结**

### 一、分页查询 ###

public void testQuerySingleTable_HQL_PagingPuery() {
        Session session = HbnUtils.getSession();
        try {
            session.beginTransaction();
    
            String hql = "from Student";
            int pageNo = 2;//当前页码
            int pageSize = 3;//每页记录数
            int firstResult =(pageNo - 1) * pageSize;//起始处
            List<Student> list = session.createQuery(hql)
            .setFirstResult(firstResult)
            .setMaxResults(pageSize)
            .list();
    
            for (Student stu : list) {
                System.out.println(stu);
            }
            session.getTransaction().commit();
            } catch (Exception e) {
                e.printStackTrace();
                session.getTransaction().rollback();
            }
        }

### 二、模糊查询 ###

public void testQuerySingleTable_HQL_Vague() {
            Session session = HbnUtils.getSession();
            try {
                session.beginTransaction();
    
                String hql = "from Student where name like:name";
                List<Student> list = session.createQuery(hql)
                                                            .setString("name", "%张%")
                                                            .list();
    
                for (Student stu : list) {
                    System.out.println(stu);
                }
                session.getTransaction().commit();
            } catch (Exception e) {
                e.printStackTrace();
                session.getTransaction().rollback();
            }
        }

### 三、聚合函数查询 ###

public void testQuerySingleTable_HQL_AggregateFunction() {
            Session session = HbnUtils.getSession();
            try {
                session.beginTransaction();
    
                String hql = "select count(id) from Student";
                Long count = (Long) session.createQuery(hql).uniqueResult();
    
                    System.out.println("一共有："+count+"条数据");
                session.getTransaction().commit();
            } catch (Exception e) {
                e.printStackTrace();
                session.getTransaction().rollback();
            }
        }

### 四、映射查询 ###

（只取某几个字段）

public void testQuerySingleTable_HQL_Mapping() {
            Session session = HbnUtils.getSession();
            try {
                session.beginTransaction();
    
                String hql = "select new Student(name,age) from Student";
                // 执行操作
                List<Student> list = session.createQuery(hql)
                        .list();
    
                for (Student stu : list) {
                System.out.println(stu);
                }
                session.getTransaction().commit();
            } catch (Exception e) {
                e.printStackTrace();
                session.getTransaction().rollback();
            }
        }

### 五、分组查询 ###

public void testQuerySingleTable_HQL_Group() {
            Session session = HbnUtils.getSession();
            try {
                session.beginTransaction();
                //查询有几个年龄段
                String hql = "select age from Student gruoup by age";
                // 执行操作
                List<Integer> list = session.createQuery(hql).list();
                // 执行操作
                for (Integer age : list) {
                System.out.println(age);
                }
                session.getTransaction().commit();
            } catch (Exception e) {
                e.printStackTrace();
                session.getTransaction().rollback();
            }
        }

### 六、命名查询 ###

**命名查询是将HQL语句配置到xml文件中，从而提高代码的可维护性，HQL语句可以配置到当前应用的任一xxx.hbm.xml文件中**  
![这里写图片描述][SouthEast]  
具体位置是在class标签后面  
![这里写图片描述][SouthEast 1]

public void testQuerySingleTable_HQL_NamedQuery() {
            Session session = HbnUtils.getSession();
            try {
                session.beginTransaction();
                //getNamedQuery("selectById")参数为配置文件里写的名字
                Student stu = (Student) session.getNamedQuery("selectById").setInteger("id", 3).uniqueResult();
                System.out.println(stu);
                session.getTransaction().commit();
    
            } catch (Exception e) {
                e.printStackTrace();
                session.getTransaction().rollback();
            }
        }

### 七、关于单表查询的效率问题 ###

在[Query接口的List方法和Iterate方法总结][Query_List_Iterate]一文中有详细讲述  
  
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[hibernate]: http://blog.csdn.net/leisure_life/article/details/61192386
[SouthEast]: https://img-blog.csdn.net/20170310152902828?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvbGVpc3VyZV9saWZl/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast
[SouthEast 1]: https://img-blog.csdn.net/20170310153240924?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvbGVpc3VyZV9saWZl/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast
[Query_List_Iterate]: http://blog.csdn.net/leisure_life/article/details/61195202