Group by hour in IQueryable

Question

In my project I receive some data from an SPS all x seconds. Every y minutes I archive the current Data in a database so I\'m able to show statistics.

The data I r

Answer 1

The key part of the GroupBy can easily be made translatable by avoiding new DateTime(...) and using either anonymous type

.GroupBy(d => new { d.ArchiveTime.Date, d.ArchiveTime.Hour })

or Date property + AddHours:

.GroupBy(d => d.ArchiveTime.Date.AddHours(d.ArchiveTime.Hour))

Unfortunately currently (EF Core 2.2) does not translate nested First / FirstOrDefault / Take(1) to SQL and uses client evaluation. For First() it is forced in order to emulate the LINQ to Objects throwing behavior, but for the other two patterns it's caused by the lack of proper translation.

The only server side solution I see for your concrete query is to not use GroupBy at all, but correlated self antijoin, something like this:

var onePerHour = dataLastWeek.Where(d => !dataLastWeek.Any(d2 =>
    d2.ArchiveTime.Date == d.ArchiveTime.Date &&
    d2.ArchiveTime.Hour == d.ArchiveTime.Hour &&
    d2.ArchiveTime < d.ArchiveTime));