Linq to NHibernate: Select multiple sums at once - sql

Question

Is there a way to select multiple sums at once using Linq to NHibernate?
Now I have
int? wordCount = (from translation in session.Query<TmTranslation>()
where translation.SatisfiesCondition
select translation.TranslationUnit)
.Sum(x => (int?)(x.WordCount + x.NumberCount)) ?? 0;
int? tagCount = (from translation in session.Query<TmTranslation>()
where translation.SatisfiesCondition
select translation.TranslationUnit)
.Sum(x => (int?)(x.TagCount)) ?? 0;
int? characterCount = (from translation in session.Query<TmTranslation>()
where translation.SatisfiesCondition
select translation.TranslationUnit)
.Sum(x => (int?)(x.CharacterCount)) ?? 0;
which generates three different SQL queries. In SQL I can grab them all three at once, but is there a way to do this in Linq to NHibernate?
Thank you.

Answer 1

this should help get you started with QueryOver way...
ResultDTO dtoAlias = null; //placeholder alias variable
var dto = session.OueryOver<TmTranslation>()
.Where(x => x.SatisfiesCondition)
//Change this to the actual type of Translation property
.JoinQueryOver<Translation>(x => x.Translation)
.SelectList(list => list
//we can sum these columns individually to keep query simple,...add them together later
.SelectSum(x => x.WordCount).WithAlias(() => dtoAlias.WordCountTotal)
.SelectSum(x => x.NumberCount).WithAlias(() => dtoAlias.NumberCountTotal)
//add more select sums to the select list
)
.TransformUsing(Transformers.AliasToBean<ResultDTO>())
.SingleOrDefault<ResultDTO>();

Answer 2

Having multiple aggregate functions within a Select() call works and results in a single SQL command sent to the database. For example:
var result = session.Query<TmAssignment>()
.Select(a => new
{
Words = session.Query<TmTranslation>().Where(s => s.Assignment == a).Sum(u => (int?) u.WordCount) ?? 0,
Others = session.Query<TmTranslation>().Where(s => s.Assignment == a).Sum(u => (int?)(u.TagCount + u.NumberCount)) ?? 0,
}).ToList();

Answer 3

A potentially simpler solution I use is to do an artificial GroupBy then project to an anonymous object:
eg.
session.Query<TmTranslation>()
.Where(o => o.SatisfiesCondition)
.Select(o => o.TranslationUnit)
.GroupBy(o => 1)
.Select(o => new
{
WordCount = o.Sum(x => (int?)(x.WordCount + x.NumberCount)) ?? 0,
TagCount = o.Sum(x => (int?)(x.TagCount)) ?? 0,
CharacterCount = o.Sum(x => (int?)(x.CharacterCount)) ?? 0
})
.Single();
This also produces just a single SQL statement and reduces the duplication nicely.