Question

Here is a cut down version of my linq query;

 var list = from inv in db.Inventories
                       where inv.InventoryCode.StartsWith("005")
                       select
                       new
                       {
                           inv.InventoryCode,
                           inv.InventoryMedias.Where(im => im.MediaType == 0).FirstOrDefault().Synopsis,
                           inv.InventoryMedias.Where(im => im.MediaType == 0).FirstOrDefault().InventoryID
                       };

…because an inventory record does not have to have any rows in InventoryMedia, i have added the .FirstOrDefault(), which then returns a null and linq is smart enough not to throw an ONSTIOO error, but i do get this error.

The cast to value type ‘Int32’ failed
because the materialized value is
null. Either the result type’s generic
parameter or the query must use a
nullable type

Now i understand that i could just change the anonymous type to a class and define this integer as a nullable type, but i dont want to do that. I have also tried using the if null command “?? 0”, but that is not supported on reference types like int. I know i can use .DefaultIfEmpty() and set a default value for the anonymous type, but how can i set a default value for the integer or is there another alternative?

Answer 1

Try projecting to the desired properties first then use FirstOrDefault(). That way you won’t have to deal with the possibility of a null reference exception and the type will be whatever is appropriate for the property. Cast to nullable if necessary.

var list = from inv in db.Inventories
           where inv.InventoryCode.StartsWith("005")
           select
           new
           {
               inv.InventoryCode,
               Synopsis = inv.InventoryMedias
                             .Where(im => im.MediaType == 0)
                             .Select(im => im.Synopsis)
                             .FirstOrDefault(),
               InventoryID = inv.InventoryMedias
                                .Where(im => im.MediaType == 0)
                                .Select(im => im.InventoryID)
                                .FirstOrDefault(),
           };