handling a null in linq to sql query

Question

I have an object like this:

public class MyObject{

  public int Prop1 {get;set;}
}

I'm doing a linq to sql query that returns a list of MyObject like this:

var TheQuery = from ....
               where ....
               select new MyObject()
               {

                 Prop1 = (...... ).Sum( d => d)

               }.ToList();

The problem is that Prop1 is a sum of a subquery and sometimes there might be nothing returned and the Sum is null, which can't be assigned to Prop1 because it's an int.

What's a good way around this.

Thanks for your suggestions.

You already asked this question stackoverflow.com/questions/6164875/… — juharr
– juharr, Commented May 29, 2011 at 3:30

BrokenGlass · Accepted Answer · 2011-05-29 03:55:36Z

1

how about using a range variable:

var TheQuery = from ....
               where ....
               let subquery = (...... )
               select new MyObject()
               {

                 Prop1 = subquery!=null ? (subquery.Sum( d => d) ?? 0) : 0;

               }.ToList();

edited May 29, 2011 at 3:55

answered May 29, 2011 at 3:23

BrokenGlass

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8 Comments

juharr Over a year ago

I could be wrong, but I think frenchie is saying that Sum returns null, not that the subquery he runs Sum on is null.

BrokenGlass Over a year ago

@juharr: according to msdn Sum() should always return a value, 0 for an empty collection.

frenchie Over a year ago

Yes, the sum returns null; the sub query could still have elements in it

BrokenGlass Over a year ago

well then indeed this question is a duplicate, you should just use Prop1 = subquery.Sum( d => d) ?? 0 - what did you not like about the previous answer? Also this means you are not using the Standard Linq Sum method, what are you using?

juharr Over a year ago

@BrokenGlass but what if this is linq-to-sql it would translate into a SQL Sum that would return null if all the values in the sum are null.

|

Anthony Pegram · Accepted Answer · 2011-05-29 03:28:32Z

1

I would simply promote your property to an int?. You have the sum of nothing, it's best to represent that as a null. The rationale is that it should be possible to have an actual sum that is 0. In this case, you do not have a sum of actual values, so keeping the null result allows you to preserve this difference.

Otherwise, you might consider (assuming the query returns the value as a nullable) invoking .GetValueOrDefault() on the result, which would normalize a null value to 0 in the case of a numeric type.

answered May 29, 2011 at 3:28

Anthony Pegram

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