help converting sql to linq expression with count

Question

I am trying to convert the following SQL into a LINQ expression

SELECT    COUNT(ID) AS Count, MyCode
FROM      dbo.Archive
WHERE     DateSent>=@DateStartMonth AND DateSent<=@DateEndMonth
GROUP BY  MyCode

and I have been trying to follow this webpage as an example:
http://stackoverflow.com/questions/606124/converting-sql-containing-top-count-group-and-order-to-linq-2-entities

I got this so far but I am stuck on understanding the new part

var res = (from p in db.Archives
           where (p.DateSent>= dateStartMonth) && (p.DateSent< dateToday)
           group p by p.MyCode into g
           select new { ??????MyCode = g.something?, MonthlyCount= g.Count() });

Thanks in advance for helping greatly appreciated Philip

Answer 1

The LINQ statement below should work:

var res = from archive in db.Archives
          where archive.DateSent >= dateStartMonth &&
                archive.DateSent < dateToday
          group archive by archive.MyCode into archiveGrp
          select new 
          { 
               MyCode = archiveGrp.Key, 
               MonthlyCount = archiveGrp.Count() 
          };

Notice that the Key property will contain the value of the property that you group on, in this case MyCode.

Answer 2

from p in archive
where p.DateSent >= dateStartMonth && p.DateSent < dateToday
group p by p.MyCode into g
select new { Count = g.Count(), MyCode = g.Key  }

produces the same output as your Sql in Linqpad

Answer 3

can you explain what g.Key is? I dont understand where that variable came from or what it is referring too? I mean what if I group on 4 different things? How would I refer to each one?

var res = from archive in db.Archives where archive.DateSent >= dateStartMonth && archive.DateSent < dateToday group archive by archive.MyCode, archive.Extra into archiveGrp select new { MyCode = archiveGrp.Key, Extra = archiveGrp.??? MonthlyCount = archiveGrp.Count() };