Question

EDIT: Simplified problem and clarified question.

I am trying to convert this Stored Procedure into a LINQ statement:

SELECT UserID, MAX(RowID) as RowID into #tempa
FROM Users
WHERE Approved = 1 
GROUP BY UserID

SELECT (bunch of columns)
FROM Users INNER JOIN #tempa
ON (Users.UserID = #tempa.UserID AND Users.RowID = #tempa.RowID)
DROP TABLE #tempa

When I run this SPROC I get 292 rows. When I try to convert it to LINQ I do the following:

IQueryable<User> userQuery = db.Users.Where(x => x.Approved == true);
        userQuery = userQuery.Where((x => x.RowID ==
                        db.Users.Where(u => u.UserID == x.UserID).Max(u => u.RowID)
           ));
         IList<User> users = userQuery.ToList();

Result is 293 rows…

Now I change the SPROC to (it’s a bitmask where value 2 is active):

SELECT UserID, MAX(RowID) as RowID into #tempa
FROM Users
WHERE Approved = 1 AND (UserAttribtues & 2) = 2
GROUP BY UserID

SELECT (bunch of columns)
FROM Users INNER JOIN #tempa
ON (Users.UserID = #tempa.UserID AND Users.RowID = #tempa.RowID)
DROP TABLE #tempa

I get 289 rows with the sproc.

Try the following with LINQ:

 IQueryable<User> userQuery = db.Users.Where(x => (x.UserAttributes & Convert.ToInt32(UserAttributes.Active)) == Convert.ToInt32(UserAttributes.Active) && x.Approved == true);
        userQuery = userQuery.Where((x => x.RowID ==
                        db.Users.Where(u => u.UserID == x.UserID).Max(u => u.RowID)
           ));

Result is 127 rows….

At first I thought it was my use of .Max in the subquery, which AD.NET corrected me below, but the numbers are way off still, what am I missing here? I’m not understanding something…

Answer 1

Something like this should work, you can refactor out some predicates from this too.

 predicate = predicate.And((x => x.RowId == 
                                        db.Users
                                             .Where(u=>u.UserId ==x.UserId)
                                             .Max(u=>u.RowId)
                           ));

You can try something like this:

var result = from u in db.Users
let max = db.Users.Where(au=>au.UserId == u.UserId).Max(au=>au.RowId)
let maxUId = db.Users.Where(au=>au.UserId == u.UserId && au.RowId == max).Select(au=>au.UserId).FirstOrDefault()
where u.RowId == max && u.UserId == maxUId
select u

Check that against the sql (strip out any other conditions please for debugging).
I think I missed the userId part, you’ll need to match the userId as well, otherwise it should not work properly. I am sure you can make the query a bit better, for example, use let to keep the whole user object which has the highest rowid and then you can use the object to match both rowid and userid.