NHibernate QueryOver subquery to return only newest record - nhibernate

Question

I have a query in Nhibernate QueryOver which brings back a collection of episode objects (episode being a spell of care) which in turn has a collection of episode statuses as a property of each episode. However I want to change this so that each episode only brings back the latest status update for that episode instead of all of them.
The SQL to do this is as follows:
SELECT *
FROM DIPEpisode e
INNER JOIN DIPEpisodeStatus s on s.EpisodeID = e.SequenceID
WHERE e.ClientID = '1000001'
AND s.SequenceID IN (
SELECT TOP 1 SequenceID
FROM DIPEpisodeStatus s
WHERE s.EpisodeID = e.SequenceID
ORDER BY StatusRecordedDate DESC
)
I have written the following query which gives me almost exactly what I need
var statuses =
QueryOver.Of<DIPEpisodeStatus>()
.OrderBy(x => x.StatusRecordedDate).Desc
.Select(x => x.Id).Take(1);
DIPEpisodeStatus statusAlias = null;
return
session.QueryOver<DIPEpisode>()
.JoinQueryOver(x => x.DIPEpisodeStatuss, () => statusAlias)
.Fetch(x => x.AgencyID).Eager
.Fetch(x => x.DIPEpisodeStatuss).Eager
.Where(e => e.ClientID.Id == this.clientId)
.WithSubquery.WhereProperty(x => x.Id).Eq(statuses)
.List();
This generates the following SQL:
SELECT *
FROM DIPEpisode this_
inner join DIPEpisodeStatus statusalia1_
on this_.SequenceID = statusalia1_.EpisodeID
WHERE statusalia1_.ClientID = '1000001' /* #p0 */
and statusalia1_.SequenceID = (SELECT TOP (1 /* #p1 */) this_0_.SequenceID as y0_
FROM DIPEpisodeStatus this_0_
ORDER BY this_0_.StatusRecordedDate desc)
As you can see, the only thing missing is the where clause from the subquery. What changes do I need to make to the query in order to generate this extra where clause and pull back only the most recent status update?
Thanks
Ben

Answer 1

the collection DIPEpisodeStatuss is always initialized with all entities because it would break changetracking otherwise. you could either define a filter for the collection or return a DTO with what you want. Also the fetch will be ignored because it can not eager load and filter in one sql statement.
NHibernate filters are explained here
defining Filters in FNH
how it would be done with a DTO
// assuming SequneceID and StatusRecordedDate correlates
var subquery = QueryOver.Of<DIPEpisode>()
.Where(e => e.ClientID.Id == this.clientId)
.JoinAlias(e => e.DIPEpisodeStatuss, () => statusAlias)
.Select(Projections.Max(() => statusAlias.SequenceID));
// or as in question
var subquery = QueryOver.Of<DIPEpisode>()
.Where(e => e.ClientID.Id == this.clientId)
.JoinAlias(e => e.DIPEpisodeStatuss, () => statusAlias)
.OrderByDescending(() => statusAlias.StatusRecordedDate)
.Select(() => statusAlias.SequenceID)
.Take(1);
DIPEpisodeDto dto = null;
DIPEpisodeStatus statusAlias = null;
return session.QueryOver<DIPEpisode>()
.Where(e => e.ClientID.Id == this.clientId)
.JoinQueryOver(e => e.DIPEpisodeStatuss, () => statusAlias)
.WithSubquery.WhereProperty(estatus => estatus.Id).Eq(statuses)
.SelectList(list => list
.Select(e => e.Whatever).WithAlias(() => dto.Whatever)
.Select(() => statusAlias.SquenceId).WithAlias(() => dto.StatusId)
...
)
.TransFormUsing(Transformers.AliasToBean<DIPEpisodeDto>())
.List();
or using LINQ
var query = from e in session.Query<DIPEpisode>()
from s in e.DIPEpisodeStatuss
where e.ClientID.Id == this.clientId
where s.Id == (
from e2 in session.Query<DIPEpisode>()
from s2 in e2.DIPEpisodeStatuss
orderby s2.StatusRecordedDate descending
select s2.Id)
.First()
select new DIPEpisodeDto
{
e.Prop1,
Status = s,
};
return query.List<DIPEpisodeDto>();