LINQ expression return null

Question

I have the following query in LINQ. "Symbol" doesn't exist, and the query is null, but I got an error, of casting and the program crashes.

decimal x = from cie in m_entities.Cie
            where cie.symbol.Equals(Symbol)
            select cie.cie_id;

Or can I have a null in x?

Answer 1

I don't think x will ever be null -- you'll just get an empty IQueryable<T> (or is it IEnumrable<T>?), where T is the datatype of cie_id.

The casting error is because you're attempting to cast the collection to a decimal.

Answer 2

Assuming that cie_id is a decimal, then try this:

decimal x = (from cie in m_entities.Cie
                     where cie.symbol.Equals(Symbol)
                     select cie.cie_id).FirstOrDefault()

Your current code tries to assign IEnumerable<decimal> to decimal, which won't work. FirstOrDefault will select the first match, if any, otherwise 0.

If you know there will be either 1 or 0 matches, you could consider SingleOrDefault instead of FirstOrDefault.