Linq - how to check if row exist if only one column is seleted in select statement

Question

Lets assume we have table as below. AlbumID and CoverType are integers with 0 as default value. In addition to AlbumID and CoverType there are other 100+ columns.

AlbumID     CoverType
1           0
2           0
3           1
4           8
6           0

In the example below, AlbumId which equals 400 do not exist.

var coverType = 
(
    from a in Albums 
    where 
        a.AlbumId == 400
    select a.CoverType
).FirstOrDefault();

As you can see I am selecting only one column and therefore var coverType is equal to zero. How I can check if this is because coverType is really zero or because row was not found? I need to distinguish between those situations

I know I can do following

var covertType = 
(
    from a in Albums 
    where 
        a.AlbumId == 400
    select a
).FirstOrDefault();

if (coverType == null)
{
}

but I would like to keep only one column in select statement (performance) and not the whole row (100+ columns). The only solution at the moment I can think about is to select at least two columns and check if coverType is null or not. However I would like to know if this is also possible with only one column selected?

Answer 1

FirstOrDefault() will give you the default value for the type you're selecting when no value is present. Since your ID column isn't nullable, that default value is 0. You could cast it to a nullable value instead.

var coverType = 
(
    from a in Albums 
    where 
        a.AlbumId == 400
    select (int?)a.CoverType
).FirstOrDefault();

Or you could select an object that only has this one field on it as a property.

var result = 
(
    from a in Albums 
    where 
        a.AlbumId == 400
    select new { a.CoverType }
).FirstOrDefault();
if (result != null)
{
    var coverType = result.CoverType;
    ...
}