很抱歉,如果这是一个愚蠢的问题,但我已经坚持这个问题一整个下午,但找不到解决方案,因为我不熟悉复杂的SQL:
我想找到“从msg发送计数>阈值的表格中发送前3位消息的用户”,这是我的标准:
Criteria c = session.createCriteria(Message.class);
ProjectionList plist = Projections.projectionList();
plist.add(Projections.groupProperty("user"));
plist.add(Projections.rowCount() , "count");
c.setProjection(plist);
c.addOrder(Order.desc("count"));
c.setFirstResult(0);
c.setMaxResults(count);
这是我可以编写的内容,但缺少“过滤行,其中rowCount低于某个阈值”。如何用标准来实现它?非常感谢!
--------------更新------------------------
谢谢@TheStijn,我试过了。我现在可以使用子查询来实现我的目标,但生成的查询不那么聪明!请参阅生成的SQL:
select
this_.fromUser as y0_,
count(*) as y1_
from
Message this_
where
this_.fromUser is not null
and this_.created>?
and this_.created<?
and ? <= (
select
count(*) as y0_
from
Message msg_
where
msg_.fromUser=this_.fromUser
and msg_.fromUser is not null
and msg_.created>?
and msg_.created<?
)
group by
this_.fromUser
order by
y1_ desc limit ?
也就是说,子查询重复了大部分主要查询,我认为这有点多余。是否有任何构建此类SQL查询的条件:
select
this_.fromUser as y0_,
count(*) as y1_
from
Message this_
where
this_.fromUser is not null
and this_.created>?
and this_.created<?
and y1_ > ? // threshold
group by
this_.fromUser
order by
y1_ desc limit ?
非常感谢!
(使用HQL这样做似乎要容易得多,但我对Criteria方式感到好奇)
答案 0 :(得分:2)
您需要一个额外的子查询,例如:
DetachedCriteria subQuery = DetachedCriteria.forClass(Message.class, "msg");
subQuery.add(Restrictions.eqProperty("msg.user", "mainQuerymsg.user"));
subQueryEntriesCount.setProjection(Projections.rowCount());
c.add(Subqueries.lt(1L, subQuery));
mainQuerymsg&lt;您的主要标准是,您需要使用别名createCriteria(MEssage.class, "alias")