NHibernate query for most recent records

Question

Ok, this should be really simple. I'm new to NHibernate, but everywhere I've searched has given me conflicting answers on this, and none of them seem to work. Basically, I need to implement the following SQL query into my code. It simply returns the most recent records for a specific participant.

select *
from result
where ParticipantId = 1
and ResultDate = (select MAX(resultDate)
                  from Result
                  where ParticipantId = 1)

I'm using Fluent NHibernate with NHibernate 3.3. I can pull back the data without the "and" in the where clause using the code below, but when I try to restrict it to the most recent records, nothing's working.

var resultSet = session.Query<Result>()
.Where(r => r.Participant.ParticipantId == 1);

Also including my domain and mapping files here for completeness. Let me know if more info is needed.

public class Result
{
    public virtual int ResultId { get; set; }
    public virtual Participant Participant { get; set; }
    public virtual ResultType ResultType { get; set; }
    public virtual float? ResultValue { get; set; }
    public virtual string ResultText { get; set; }
    public virtual DateTime ResultDate { get; set; }
    public virtual int? Systolic { get; set; }
    public virtual int? Diastolic { get; set; }
    public virtual DateTime? DateAdded { get; set; }
    public virtual string AddedBy { get; set; }
    public virtual DateTime? DateChanged { get; set; }
    public virtual string ChangedBy { get; set; }
}

public ResultMap() 
{
    Table("Result");
    LazyLoad();
    Id(x => x.ResultId).GeneratedBy.Identity().Column("ResultId");
    References(x => x.Participant).Column("ParticipantId");
    References(x => x.ResultType).Column("ResultTypeId");
    Map(x => x.ResultValue).Nullable();
    Map(x => x.ResultText).Nullable().Length(100);
    Map(x => x.ResultDate).Nullable();
    Map(x => x.Systolic).Nullable();
    Map(x => x.Diastolic).Nullable();
    Map(x => x.DateAdded).Nullable();
    Map(x => x.AddedBy).Nullable().Length(100);
    Map(x => x.DateChanged).Nullable();
    Map(x => x.ChangedBy).Nullable().Length(100);
}

Any thoughts on an easy solution to get the recent data? Bonus points for letting me know how to get the last 2 dates, as I'll need them soon for comparing improvements. Thanks in advance!

Answer 1

To get that same query via QueryOver...

var maxResultDate = QueryOver.Of<Result>()
    .Where(x => x.Participant.ParticipantId  == 1)
    .Select(Projections.Max<Result>(x => x.ResultDate));

var rslt = s.QueryOver<Result>()
    .Where(x => x.Participant.ParticipantId == 1)
    .WithSubquery.WhereProperty(x => x.ResultDate).Eq(maxResultDate)
      //or to get the "last" 2 rows...
      //.OrderBy(x => x.ResultDate).Desc
      //.Take(2)
    .List();