今天做一个稍微复杂的查询,是用来统计的,但是报错:
Cannot create TypedQuery for query with more than one return using requested result type
代码如下:
1. NamedQuery:
@NamedQuery(name = "Detect.CountByUnitAndResultDx", query = "select " + "a.detectUnitId, " + "count(*) as total, " + "(select count(*) from Detect a where a.resultDx = 1 and a.detectUnitId =:detectUnitId) as good, " + "(select count(*) from Detect a where a.resultDx = 0 and a.detectUnitId =:detectUnitId) as bad " + "from Detect a " + "where a.detectUnitId = :detectUnitId")
2. 查询代码:
TypedQuery<DetectCountOfUnit> query = em.createNamedQuery("Detect.CountByUnitAndResultDx", DetectCountOfUnit.class);//这句报错 query.setParameter("detectUnitId", id); List<DetectCountOfUnit> counts = query.getResultList(); if(counts !=null ){ detectCountOfUnit = counts.get(0); }
网上找原因,找了一圈,在StackOverflow上面找到了答案,原因如下:
在TypedQuery里面,指定了DetectCountOfUnit.class这个类,但是在查询语句中,返回的却是不同的几个字段:
a.detectUnitId,
count(*) as tatal,
(select .....,
所以会报错,也就是返回类型并不匹配,Hibernate无法将分散的字段拼起来填到一个类中。那怎样才能匹配呢?
如果要改查询语句,那至少要改成如下形式:
select a from DetectCountOfUnit a ...
如果要改查询代码,那么改法大致如下:
Query query = em.createNamedQuery("Detect.CountByUnitAndResultDx"); query.setParameter("detectUnitId", id); object = query.getSingleResult();这个返回的object,在服务器端没法处理,直接返回给客户端好了,是字符串数组的形式,例如:[160105, 40, 35, 5],也就是和数据库里查出来的结果集形式一致。
如果返回多行记录,那么就用Object[]