Question

I have

var result =  (from rev in Revisions 
   join usr in Users on rev.UserID equals usr.ID
    join clc in ChangedLinesCounts on rev.Revision equals clc.Revision
    select new {rev.Revision, 
    rev.Date, usr.UserName, usr.ID, clc.LinesCount}).Take(6);

I make a couple of joins on different tables, not relevant for this question what keys are, but at the end of this query my result “table” contains

{Revision, Date, UserName, ID, LinesCount}

Now I execute e GroupBy in order to calculate a total lines count per user.

So..

from row in result group row by row.ID into g  {1}
    select new { 
        g.Key,
        totalCount = g.Sum(count=>count.LinesCount)
    };

So I get a Key=ID, and totalCount=Sum, but

Confusion

I would like to have also other fields in final result.
In my understanding “table” after {1} grouping query consist of

{Revision, Date, UserName, ID, LinesCount, TotalCount}

If my assumption is correct, why I can not do something like this:

from row in result group row by row.ID into g  {1}
        select new { 
            g.Key,
                g.Revision //Revision doesn't exist ! Why ??
            totalCount = g.Sum(count=>count.LinesCount)
        };

but

from row in result group row by row.ID into g  {1}
            select new { 
                g.Key,
                    Revision = g.Select(x=>x.Revision), //Works !
                totalCount = g.Sum(count=>count.LinesCount)
            };

Works !, but imo, sucks, cause I execute another Select.

Infact looking on LinqPad SQL output I get 2 SQL queries.

Question

Is there any elegant and optimal way to do this, or I always need to run Select
on groupped data, in order to be able to access the fields, that exists ?

Answer 1

The problem is, that you only group by ID – if you’d do that in SQL, you couldn’t access the other fields either…

To have the other fields as well, you have to include them in you group clause:

from row in result group row by new { row.ID, row.Revision } into g
    select new { 
        g.Key.ID,
        g.Key.Revision
        totalCount = g.Sum(count=>count.LinesCount)
    };