Question

I am trying to get the below linq query to return -1 if there isn’t any current value. I was looking at this article on MSDN, here, and it seemed that DefaultIfEmpty() was what I wanted.

Unfortunately, I am getting a The type arguments cannot be inferred from the usage. Try specifying the type arguments explicitly. error.

I guess I am not sure what that means or what it is telling me to do. Can someone explain, please.

 public static int CheckForDRIID(int personID)
    {
        using (var context = ConnectDataContext.Create())
        {
            var masterIndex =
                (from applicationAssociation in context.tblApplicationAssociations
                 where applicationAssociation.ApplicationID == 1 && applicationAssociation.PersonID == personID
                 select applicationAssociation.PersonApplicationID).DefaultIfEmpty(-1).Single();


            return Convert.ToInt32(masterIndex);
        }
    }

Answer 1

-1 is an int and applicationAssociation.PersionApplicationID isn’t, so it doesn’t know what to return. You could replace -1 with the same type as applicationAssociation.PersionApplicationID, “-1”. Or specify the type like DefaultIfEmpty<string>. And a third options is to do the Convert.ToInt32 in the select.