hibernate-hql 实战小结

Question

查询报名记录

select o.id as id, o.name as org_name from t_sign_up t,
t_student s, t_org o where t.student_id = s.id and s.org_id=o.id

结果如下，可以看到 1 个单位下有 4 条报名记录，另外一个单位下有 2 条：

汇总报名记录，并按照统计次数降序：

select o.id as id, o.name as org_name, count(t.id) as org_count
from t_sign_up t, t_student s, t_org o where t.student_id = s.id
and s.org_id=o.id group by o.name order by org_count desc

效果如下：

如上 sql，在 Mysql 测试成功，移植到 hql 时，需要给经过重名的 orgCount 加上引号，否则会报出现报错，报找不到 orgCount 字段，如下：

select o.id as id, o.name as orgName, count(t.id) as orgCount
from SignUp t, Student s, Org o where t.studentId = s.id
and s.orgId=o.id group by o.name order by 'orgCount' desc

数据比较多的时候，需要进行分页展示，相关的，我们要构建 countQuery 来查询结果总数目，在如上的 sql 上进行统计，如下：

String countQuery = "select count(*) from
(select o.id as id, o.name as orgName, count(t.id) as orgCount
from SignUp t, Student s, Org o where t.studentId = s.id
and s.orgId=o.id group by o.name) as result"

执行过程中，会报错：

九月 08, 2017 3:22:22 下午 org.hibernate.hql.ast.ErrorCounter reportError
严重: line 1:61: unexpected token: count
ERROR 2017 09 08 15:22:22 com.opensymphony.xwork2.util.logging.commons.CommonsLogger.error(CommonsLogger.java:42) Exception occurred during processing request: unexpected token: ( near line 1, column 22 [select count(*) from (select o.id as id, o.name as orgName, count(t.id) as orgCount from com.lmscn.lms.model.SignUp t, com.lmscn.lms.model.Student s, com.lmscn.lms.model.Org o where t.studentId = s.id and s.orgId=o.id group by o.name) as result]; nested exception is org.hibernate.hql.ast.QuerySyntaxException: unexpected token: ( near line 1, column 22 [select count(*) from (select o.id as id, o.name as orgName, count(t.id) as orgCount from com.lmscn.lms.model.SignUp t, com.lmscn.lms.model.Student s, com.lmscn.lms.model.Org o where t.studentId = s.id and s.orgId=o.id group by o.name) as result] 
org.springframework.orm.hibernate3.HibernateQueryException: unexpected token: ( near line 1, column 22 [select count(*) from (select o.id as id, o.name as orgName, count(t.id) as orgCount from com.lmscn.lms.model.SignUp t, com.lmscn.lms.model.Student s, com.lmscn.lms.model.Org o where t.studentId = s.id and s.orgId=o.id group by o.name) as result]; nested exception is org.hibernate.hql.ast.QuerySyntaxException: unexpected token: ( near line 1, column 22 [select count(*) from (select o.id as id, o.name as orgName, count(t.id) as orgCount from com.lmscn.lms.model.SignUp t, com.lmscn.lms.model.Student s, com.lmscn.lms.model.Org o where t.studentId = s.id and s.orgId=o.id group by o.name) as result]
	at org.springframework.orm.hibernate3.SessionFactoryUtils.convertHibernateAccessException(SessionFactoryUtils.java:660)
	at org.springframework.orm.hibernate3.HibernateAccessor.convertHibernateAccessException(HibernateAccessor.java:412)
	at org.springframework.orm.hibernate3.HibernateTemplate.doExecute(HibernateTemplate.java:411)
	at org.springframework.orm.hibernate3.HibernateTemplate.execute(HibernateTemplate.java:339)
	at javacommon.base.BaseHibernateDao$PageQueryUtils.pageQuery(BaseHibernateDao.java:151)
	at javacommon.base.BaseHibernateDao$PageQueryUtils.access$1(BaseHibernateDao.java:147)
	at javacommon.base.BaseHibernateDao.pageQuery(BaseHibernateDao.java:121)

还是 hibernate 解析过程中出了问题，主要是对中间产生的 result 虚拟临时表 没有办法识别，难道这就要放弃，只能使用 JDBC 来进行分页了？
不然！经过思考，我们统计 count 的目的就是为了得到总数，也有一个折中的办法，如下：
使用 distinct 进行去重，这样查到两条记录（也就是说共有两个单位），如下：

select count(distinct o.id) from t_sign_up t, t_student s,
t_org o where t.student_id = s.id and s.org_id=o.id

转换成 hql，如下：

String countQuery = "select count(distinct o.id) from SignUp t, Student s, Org o where t.studentId = s.id and s.orgId=o.id";

结果如下：

可以看到，分页成功了：