Linq query with nullable sum

Question

from i in Db.Items
select new VotedItem
{
    ItemId = i.ItemId,
    Points = (from v in Db.Votes
              where b.ItemId == v.ItemId
              select v.Poi         


        

Answer 1

Just to add another method into the mix :)

Where(q=> q.ItemId == b.ItemId && b.Points.HasValue).Sum(q=>q.Points.Value)

I had a similar scenario but I wasn't comparing an additional field when summing...

Where(q => q.FinalValue.HasValue).Sum(q=>q.FinalValue.Value);

Answer 2

You want to use the nullable form of Sum, so try casting your value to a nullable:

from i in Db.Items
select new VotedItem
{
    ItemId = i.ItemId,
    Points = (from v in Db.Votes
              where b.ItemId == v.ItemId
              select v.Points).Sum(r => (decimal?) r.Points)
}

Your issue is discussed here in more detail:

http://weblogs.asp.net/zeeshanhirani/archive/2008/07/15/applying-aggregates-to-empty-collections-causes-exception-in-linq-to-sql.aspx

Answer 3

I had a similar issue and came up with the solution of getting whatever I was trying to get out of the database, do a count on those and then only if I had anything returned do a sum. Wasn't able to get the cast working for some reason so posting this if anyone else had similar issues.

e.g.

Votes = (from v in Db.Votes
          where b.ItemId = v.ItemId
          select v)

And then check to see if you've got any results so that you don't get null returned.

If (Votes.Count > 0) Then
    Points = Votes.Sum(Function(v) v.Points)
End If

Answer 4

Thought I would throw another solution out there. I had a similar issue and this is how I ended up solving it:

Where(a => a.ItemId == b.ItemId && !b.IsPointsNull()).Sum(b => b.Points)

Answer 5

Assuming "v.Points" is a decimal just use the following:

from i in Db.Items
select new VotedItem
{
    ItemId = i.ItemId,
    Points = (from v in Db.Votes
              where b.ItemId == v.ItemId
              select (decimal?) v.Points).Sum() ?? 0
}

Answer 6

Try to check this out:

var count = db.Cart.Where(c => c.UserName == "Name").Sum(c => (int?)c.Count) ?? 0;

So, the root of the problem is that SQL query like this:

SELECT SUM([Votes].[Value])
FROM [dbo].[Votes] AS [Votes]
WHERE 1 = [Votes].[UserId] 

returns NULL