HQL: Aggregate function on single column, list returned

d.trilsbeek · **Joined:** Wed Sep 13, 2006 4:12 am **Posts:** 10

Hello everyone,

i'm trying to retrieve a single datetime value using an hql query:

Code:

select min(Answers.Created) from Answers aw where aw.Contactid.Id = 10 and aw.Formid.Id = 1002

executed via ISession.CreateQuery().UniqueResult() this query throws an NonUniqueResultException. When executed by ISession.CreateQuery().List() i get a collection of Answers-Objects (all objects that fit into the where-clause). Shouldn't i just get a single object of type DateTime when selecting a single property? The selected Property is mapped as a simple Property of type DateTime, not nullable.

Any suggestions?

jta · **Posted:** Wed Mar 12, 2008 8:14 am

Lets se the CreateQuery and UniqueResult parts of the query, code like below should work fine:

Code:

DateTime dt = s.CreateQuery("select min(a.Created) from Answer a").UniqueResult<DateTime>();

d.trilsbeek · **Joined:** Wed Sep 13, 2006 4:12 am **Posts:** 10

sorry, this still leads to an NHibernate.NonUniqueResultException. I think i'm going to make a short workaround for this and investigate my problem within a small sample project. Maybe there is something about my mapping or class definitions that causes this behavior.

wolli · **Posted:** Wed Mar 12, 2008 10:03 am

Try it with aw.Created instead of Answers.Created. I ran into a similar problem a few days ago and found out that you have to use the alias in the select if you specify one in the from clause. Otherwise you get the object instead of the selected properties.

Code:

select min(aw.Created) from Answers aw where aw.Contactid.Id = 10 and aw.Formid.Id = 1002

I can't remember reading that explicitly in the documentation, but that my rather be due to my reading ... ;-)

d.trilsbeek · **Joined:** Wed Sep 13, 2006 4:12 am **Posts:** 10

thats it, using the alias within the aggregate function works. I wonder if this behavior is intended.

Thank you!