Question

I have a table that has the following 3 columns, ID, ShortCode, UploadDate.

I want to use LINQ to group the results by shortcode (and keep all the results) then order those groups and return a list.

I have the following:

 rawData.Provider.CreateQuery<PDFDocument>(qb.rootExperession)
.ToList<PDFDocument>().
GroupBy(b=>b.ShortCode)
.SelectMany(b=>b).ToList<PDFDocument>()

I want to return all results, grouped by ShortCode, the items within each group sorted by UploadDate and the groups sorted so the one that has the most recent document in it first.

Does anyone know if this is even possible?

Answer 1

Try

rawData.Provider.CreateQuery<PDFDocument>(qb.rootExperession)
    .AsEnumerable()
    .OrderByDescending(d => d.UploadDate)
    .GroupBy(d => d.ShortCode)
    .SelectMany(g => g)
    .ToList();

This should

• Order the items by upload date (descending so newest first)
• Then group them by short code – so within each group the items are still sorted
• The groups are still in descending order, so no need to order again
• Finally concatenate the results into a single list

If performance is an issue you many be better off doing

rawData.Provider.CreateQuery<PDFDocument>(qb.rootExperession)
    .AsEnumerable()
    .GroupBy(d => d.ShortCode)
    .Select(g => g.OrderByDescending(d => d.UploadDate))
    .OrderByDescending(e => e.First().UploadDate)
    .SelectMany(e => e)
    .ToList();

which sorts the contents of each group separately rather than sorting everything first and then grouping.