Question

I’m experimenting with Linq and am having trouble figuring out grouping. I’ve gone through several tutorials but for some reason can’t figure this out.

As an example, say I have a table (SiteStats) with multiple website IDs that stores a count of how many visitors by type have accessed each site in total and for the past 30 days.

╔════════╦═════════════╦════════╦══════╗ ║ SiteId ║ VisitorType ║ Last30 ║ Total║ ╠════════╬═════════════╬════════╬══════╣ ║      1 ║           1 ║     10 ║  100 ║ ║      1 ║           2 ║     40 ║  140 ║ ║      2 ║           1 ║     20 ║  180 ║ ╚════════╩═════════════╩════════╩══════╝ 

In SQL, I can easily get the counts for SiteID 1 with the following:

SELECT SiteId,          SUM(Last30) AS Last30Sum   FROM Sites   WHERE SiteId = 1   GROUP BY SiteId 

and should get a row like…

╔════════╦════════════╗ ║ SiteId ║ Last30Total║ ╠════════╬════════════╣ ║      1 ║         50 ║ ╚════════╩════════════╝ 

However I’m not sure how to get this result using Linq. I’ve tried:

var statsRecord = from ss in db.SiteStats       where ss.SiteId == siteId       group ss by ss.SiteId into ss       select ss; 

but I’m not able to get back the total with something like statsRecord.Last30

Can someone please let me know where I’m going wrong? Any help is appreciated.

Answer 1

Actually, although Thomas’ code will work, it is more succint to use a lambda expression:

var totals = from s in sites group s by s.SiteID into grouped select new {     SiteID = grouped.Key,     Last30Sum = grouped.Sum( s => s.Last30 ) }; 

which uses the Sum extension method without the need for a nested LINQ operation.

as per the LINQ 101 examples – http://msdn.microsoft.com/en-us/vcsharp/aa336747.aspx#sumGrouped