Apply ISNULL like SQL in LINQ

Question

I have the next LINQ where o.Value and p.Value are decimal types

from o in dbContext.Ammounts
where o.Value > (from p in dbContext.Payments select p).Sum(p => p.Value))

The inner LINQ from p in dbContext.Payments select p).Sum(p => p.Value) can be return a NULL value and I need to apply a ISNULL(linq_sentence, 0)

I try with this:

from o in dbContext.Ammounts
where o.Value > ((from p in dbContext.Payments select p).Sum(p => p.Value)) ?? 0m)

But I get this message error:

Operator '??' cannot be applied to operands of type 'decimal' and 'decimal'

Answer 1

When the collection is empty in Linq2SQL the aggregate returns null. If the value being aggregated is non nullable this will throw an exception. To solve the problem, cast the value being aggregated to a nullable type.

from o in dbContext.Ammounts
where o.Value > ((from p in dbContext.Payments select p)
                .Sum(p => (decimal?)p.Value)) ?? 0m);

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