Sum of a subquery in NHibernate - sql

Question

I am using NHibernate 3.3.1.4000.
Here's what I would like to achieve:
SELECT sum(tr_time)
FROM (SELECT seg.translation_time as tr_time
FROM "TRANSLATION" seg
WHERE seg.translation_time > 0 and seg.fk_id_language = 34
ORDER BY seg.translation_time ASC
LIMIT 1000) as subquery
The easiest way, using LINQ to NHibernate, fails with a NotSupportedException:
session.Query<Translation>()
.Where(s => s.Language == language && s.TranslationTime > 0)
.OrderBy(s => s.TranslationTime)
.Take(1000)
.Select(s => s.TranslationTime)
.Sum(s => s);
I was able to produce this SQL:
SELECT sum(this_.translation_time) as y0_
FROM "TRANSLATION" this_
WHERE this_.id in (SELECT this_0_.id as y0_
FROM "TRANSLATION" this_0_
WHERE this_0_.fk_id_language = 34
and this_0_.translation_time > 0
ORDER BY this_0_.translation_time asc
LIMIT 1000)
with the following query:
session.QueryOver<Translation>(() => translationAlias)
.WithSubquery.WhereProperty(s => s.Id)
.In(QueryOver.Of<Translation>(() => translationSubAlias)
.Where(s => s.Language == language)
.Where(s => s.TranslationTime > 0)
.Select(s => s.Id)
.OrderBy(s => s.TranslationTime).Asc
.Take(1000))
.Select(Projections.ProjectionList()
.Add(Projections.Sum(Projections.Property(() => translationAlias.TranslationTime))))
.FutureValue<Int32>();
However, that's obviously not ideal as the WHERE ... IN clause is not necessary.
I tried things like
session.QueryOver<Translation>(() => translationAlias)
.Select(Projections.ProjectionList()
.Add(Projections.Sum(
Projections.Alias(
Projections.SubQuery(
QueryOver.Of<Translation>(() => translationSubAlias)
.Where(() => translationSubAlias.Language == language)
.Where(() => translationSubAlias2.TranslationTime > 0)
.Select(Projections.Property("TranslationTime"))), "tr_time"))))
.FutureValue<Int32>()
but it generates this SQL:
SELECT sum((SELECT this_0_.translation_time as y0_
FROM "TRANSLATION" this_0_
WHERE this_0_.fk_id_language = 34 and this_0_.translation_time > 0)) as y0_
FROM "TRANSLATION" this_
which the database server rejects with the following error message: more than one row returned by a subquery used as an expression
I don't really care which method I would eventually use (LINQ, QueryOver, Criteria API) as long as it allows future queries.

Answer 1

Any chance it is not returning any values? If that is the case, you need to make TranslationTime nullable:
session.Query<Translation>()
.Where(s => s.Language == language && s.TranslationTime > 0)
.OrderBy(s => s.TranslationTime)
.Take(1000)
.Select(s => s.TranslationTime)
.Sum(s => (int?) s);
Notice the "int?" cast, assuming TranslationTime is of type int.