C# – NHibernate Aggregate Subquery

cnetnhibernatesql server

I have a problem with NHibernate that I don't seem to be able to find a simple way around.

I have the following database:

Game: ID, Score, Match_ID

Match: ID

A match consists of 3 games.

I want to find out what the maximum Match score is, so the following SQL would do the trick:

select max(a.total) from 
  (select Match.ID, sum(Game.Score) as total 
     from Game inner join Match
     on Game.Match_ID = Match.ID
     group by Match.ID) a

In NHibernate, this appears to be a bit trickier. Apparently, HQL does not allow subqueries in the from clause, so I can't really use this.

I'm pretty sure that it can be done with ICriteria, but I've only just started using NH so I can't seem to figure it out. I've basically got to the following:

Session.CreateCriteria<Game>()
    .SetProjection(Projections.ProjectionList()
        .Add(Projections.GroupProperty("Match"))
        .Add(Projections.Sum("Score"))).List();

After that I've played around with various assortments of DetachedCriteria, but just seem to be going round in circles.

Best Answer

For the HQL world a single query does the trick...

var maxScore = session.CreateQuery(@"select sum(game.Score) 
                                     from Game game 
                                     group by game.Match
                                     order by sum(game.Score) desc")
                      .SetMaxResults(1)
                      .UniqueResult<long>();

Hope this helps..

Update: And for the Criteria world, may be there is a better result transformation but this just works :)

var max = (int)session.CreateCriteria<Game>("game")
    .SetProjection(Projections.ProjectionList()
                       .Add(Projections.GroupProperty("game.Match"))
                       .Add(Projections.Sum("game.Score"), "total"))
    .AddOrder(Order.Desc("total"))
    .SetMaxResults(1)
    .SetResultTransformer(Transformers.AliasToEntityMap)
    .UniqueResult<IDictionary>()["total"];
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