BLToolKit, Linq Query, SQL Not what I expected

Question

I am using BLToolKit in a project of mine and I was trying to get this to work. What I don't like is that I am trying to average a bunch of temps down to the minute, but the select statement that is being generated groups by the minute but then selects the original time. I think I am doing the linq expression correctly (but then again, i am not getting the results i expect). (this is C#, if you care) Anyone know what is going wrong?

                 var test = (from r in db.SensorReadingRaws
                        where r.TimeLogged < DateTime.Now.AddMinutes(-2)
                        group r by new
                        {
                            Sensor = r.SensorNumber,
                            //group time down to the minute
                            Time = r.TimeLogged.AddSeconds(-1 * r.TimeLogged.Second).AddMilliseconds(-1 * r.TimeLogged.Millisecond)
                        } into grouped
                        select new SensorReading
                        {
                            SensorNumber = grouped.Key.Sensor,
                            TimeLogged = grouped.Key.Time,
                            Reading = (int)grouped.Average(x => x.Reading)
                        }).ToList();

            textBox1.Text = db.LastQuery;

and the resulting query is this

SELECT
[r].[SensorNumber],
[r].[TimeLogged],
Avg([r].[Reading]) as [c1]
FROM
[SensorReadingRaw] [r]
WHERE
[r].[TimeLogged] < @p1
GROUP BY
[r].[SensorNumber],
DateAdd(Millisecond, Convert(Float, -DatePart(Millisecond, [r].[TimeLogged])), DateAdd(Second, Convert(Float, -DatePart(Second, [r].[TimeLogged])), [r].[TimeLogged])),
[r].[TimeLogged]

Answer 1

I discovered that

BLToolkit.Data.Linq.Sql.AsSql<T>(T obj)

can be used as a workaround for this case.

When applying this function to the required grouped key properties in select statement you get rid of grouping/selecting an original field.

It may look something like:

_queryStore.Leads().
    GroupBy(x => new {
        x.LeadDate.Hour,
        x.LeadDate.Minute
    }).
    Select(x => new {
        Hour = Sql.AsSql(x.Key.Hour),
        Minute = Sql.AsSql(x.Key.Minute),
        Count = x.Count()
    });

and in your particular case:

                 var test = (from r in db.SensorReadingRaws
                        where r.TimeLogged < DateTime.Now.AddMinutes(-2)
                        group r by new
                        {
                            Sensor = r.SensorNumber,
                            //group time down to the minute
                            Time = r.TimeLogged.AddSeconds(-1 * r.TimeLogged.Second).AddMilliseconds(-1 * r.TimeLogged.Millisecond)
                        } into grouped
                        select new SensorReading
                        {
                            SensorNumber = grouped.Key.Sensor,
                            TimeLogged = Sql.AsSql(grouped.Key.Time),
                            Reading = (int)grouped.Average(x => x.Reading)
                        }).ToList();

Answer 2

I got same issue yesterday. Today I found a workaround. The idea is to write 2 linq queries. First transforming the data and the second grouping the result:

var bandAndDate =
    (from r in repo.Entities
    select new {Band = r.Score / 33, r.StartTime.Date});

var examsByBandAndDay =
    (from r in bandAndDate
    group r by new {r.Band, r.Date } into g
    select new { g.Key.Date, g.Key.Band, Count = g.Count() }).ToList();

Both this queries run one SQL that do the job:

SELECT
    [t1].[c1] as [c11],
    [t1].[c2] as [c21],
    Count(*) as [c3]
FROM
(
    SELECT
        [r].[Score] / 33 as [c2],
        Cast(Floor(Cast([r].[StartTime] as Float)) as DateTime) as [c1]
    FROM
        [Results] [r]
) [t1]
GROUP BY
    [t1].[c2],
    [t1].[c1]