Question

The linq query below is not returning results that have been ordered by the sequence field in decending order. Instead the results are returned without regard to the orderby:

var qr = from l in reports.layouts
    where l.job == jobNumber
    orderby l.sequence descending
    group l by l.filename;

However the code below is able to return the results grouped by the filename field, and ordered decending by the sequence field:

var qr = reports.layouts
   .Where(l => l.job == jobNumber)
   .OrderBy(l => l.filename)
   .GroupBy(l => l.filename, (l, c) => c.OrderByDescending(x => x.sequence));

Can anyone offer any insight as to how the first query should be written to return the results in the desired descending sequence?

Answer 1

Grouping destroys the order. Your two queries are not the same.

The first translates into something more like:

var qr = reports.layouts
   .Where(l => l.job == jobNumber)
   .OrderByDescending(l => l.sequence)
   .GroupBy(l => l.filename);

Since the GroupBy happens after the ordering, it effectively destroys the ordering.

Personally, this is one case where I find the method chain syntax you’ve used much more clear in terms of intent than an equivalent query syntax.