I'm trying to create a query along the line of

select
new ReportItem(
count(case when date - getdate() > 10 then 1 else 0 end)
count(case when date - getdate() > 20 then 1 else 0 end)
count(case when date - getdate() > 30 then 1 else 0 end)
...
)
from class
group by classid

but apparently hql doesn't support "case when" in "select", what's my alternate for queries like these, I thought about using a iif UDF but that will kill the performance, subqueries will make the hql statement very lengthly, is there any other options?

After a little digging around I found that there is no support for subquery in select either, therefore that option is out.

hibernate implemented "select case when" as mentioned in HHH-467, any chance that nhibernate can do the same thing in the near future?

Hmm, it's a Hibernate 3 feature, so I doubt about the near future. But please create an issue in JIRA so that we know it's wanted.