Question

When Executing the following linq to sql statement:

    var stuff = from l in _db.SqlLinks                 select new                            {                                Link = l,                                Rating = (from v in l.SqlLinkVotes                                          where v.Tag == tagId                                                && v.VoteDate >= since                                          select v.Vote).Sum(),                                NumberOfVotes = (from v in l.SqlLinkVotes                                                 where v.Tag == tagId                                                       && v.VoteDate >= since                                                 select v.Vote).Count(),                                NumberOfComments = (from v in l.SqlLinkVotes                                                    where v.Tag == tagId                                                          && v.VoteDate >= since                                                          && v.Comment != ''                                                    select v.Vote).Count()                            }; 

I get a System.InvalidOperationException (null value cannot be assigned to Int32).

Through debugging I’ve seen that this comes from the Rating property of the dynamic object.

When there are no SqlLinkVotes for a particular link the Sum() results in a null value, but Rating is an int, and linq to sql thinks the Sum() will result in an int, not a nullable int.

I could easily write a stored procedure to get around this, but I thought it was a good way for me to understand linq to sql more.

Please help!

Answer 1

There’s a Connect thread about this which suggests that you cast the result of Sum() to a nullable type (int? in your case). I suspect if you want the rating to be non-nullable, you can then use the null-coalescing operator:

Rating = ((int?) (from v in l.SqlLinkVotes                   where v.Tag == tagId                      && v.VoteDate >=                    select v.Vote).Sum()) ?? 0 

It’s worth a try, anyway.