Question

Came across a problem whereby I wanted the last time data was imported to show failures. I ended up resorting to HQL because I had to execute two queries can anyone see why this doesn’t work (properly) in Linq to NHibernate, is it a known bug in 3.1?

The sql I would write.

select JobImport.* from 
JobImportResult
inner join (
    select Max(JobImportResultId) as JobImportResultId 
    from JobImportResult
    group by JobImportId
)as tbl on tbl.JobImportResultId = JobImportResult.JobImportResultId
inner join JobImport on JobImport.JobImportId = JobImportResult.JobImportId
where ImportFailureReasonId is not null

The HQL I ended up writing.

select jir.JobImport from JobImportResult jir where jir.Id in 
(select max(mjir.Id) from JobImportResult mjir group by mjir.JobImport)
and jir.ImportFailureReason is not null

The Linq that works(but I think will break after 2000 rows)

var innerQuery = Query<JobImportResult>()
    .GroupBy(jir=>jir.JobImport)
    .Select(jir=>jir.Max(jr=>jr.Id));

var innerQueryListed = innerQuery.ToList();

var resultQuery = Query<JobImportResult>()
    .Where(jir => innerQueryListed.Contains(jir.Id) && jir.ImportFailureReason != null)
    .Select(jir => jir.JobImport);

The Linq that doesn’t work 🙁

var innerQuery = Query<JobImportResult>()
.GroupBy(jir=>jir.JobImport)
.Select(jir=>jir.Max(jr=>jr.Id));

var resultQuery = Query<JobImportResult>()
.Where(jir => innerQuery.Contains(jir.Id) && jir.ImportFailureReason != null)
.Select(jir => jir.JobImport);

Answer 1

Are you using .NET 4? If so, try this:

var innerQuery = Query<JobImportResult>()
    .GroupBy(jir=>jir.JobImport)
    .Select(jir=>jir.Max(jr=>jr.Id))
    .ToList();

var resultQuery = Query<JobImportResult>()
    .Where(jir => innerQuery.Any(j => j == jir.Id)
        && jir.ImportFailureReason != null)
    .Select(jir => jir.JobImport)
    .ToList(); //only use this if you want to resolve the query

Or .NET 3.5 change the resultQuery part to be:

var resultQuery = Query<JobImportResult>()
    .Where(jir => innerQuery.Count(j => j == jir.Id) > 0
        && jir.ImportFailureReason != null)
    .Select(jir => jir.JobImport)
    .ToList(); //only use this if you want to resolve the query