Hi,

I've encountered a strange exception:

I'm trying to do a rather innocent sum:

decimal total = myEntity.Lines.Sum(l => l.Amount.GetValueOrDefault());

This throws an exception:

L'exception System.InvalidCastException s'est produite
  Message="Unable to cast null value to System.Decimal; use System.Decimal? instead."
  Source="Xtensive.Core"
  StackTrace:
       à Xtensive.Core.Tuples.Tuple.GetValueOrDefault[T](Int32 fieldIndex)
       à lambda_method(ExecutionScope , Object[] , Tuple , ItemMaterializationContext )
       à System.DelegateBindExtensions.<>c__DisplayClassa`4.<Bind>b__9(T2 arg2, T3 arg3)
       à Xtensive.Storage.Linq.Materialization.MaterializationHelper.<>c__DisplayClass4`1.<Materialize>b__3(Tuple tuple)
       à System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
       à System.EnumerableExtensions.<Batch>d__27`1.MoveNext()
       à System.EnumerableExtensions.<ApplyBeforeAndAfter>d__2f`1.MoveNext()
       à Xtensive.Storage.TransactionalExtensions.<ToTransactional>d__0`1.MoveNext()
       à System.Linq.Enumerable.<SelectManyIterator>d__14`2.MoveNext()
       à System.Linq.Enumerable.First[TSource](IEnumerable`1 source)
       à lambda_method(ExecutionScope , Object[] , IEnumerable`1 , Dictionary`2 , ParameterContext )
       à System.DelegateBindExtensions.<>c__DisplayClass13`5.<Bind>b__12(T2 arg2, T3 arg3, T4 arg4)
       à Xtensive.Storage.Linq.TranslatedQuery`1.Execute(ParameterContext parameterContext)
       à Xtensive.Storage.Linq.QueryProvider.Execute[TResult](Expression expression)
       à System.Linq.Queryable.Sum[TSource](IQueryable`1 source, Expression`1 selector)

I've tried to create a small sample but naturally the sample runs just fine... ;)

Any thought on this problem?

Updated at 04.05.2010 7:36:49

Hello,

Here is the file version of Xtensive.Storage : 1.0.4870.60138 (latest 4.2 release)

For the model, I will try to build a model reproducing the bug, but I've not been successful for now.

Regards,

Updated at 04.05.2010 7:58:26

Ok, I found the problem: it happens when doing the sum of an empty Entiset<t> on a Nullable type column

Model:

[Serializable]
  [HierarchyRoot]
  public class MyEntity : Entity
  {
    [Field, Key]
    public int Id { get; private set; }

    [Field, Association(PairTo = "Owner")]
    public EntitySet<Line> Lines { get; private set; }
  }

  [HierarchyRoot]
  public class Line : Entity
  {
    [Field, Key]
    public int Id { get; private set; }

    [Field]
    public MyEntity Owner { get; set; }

    [Field]
    public decimal? Amount { get; set; }
  }

Test code:

using (Session.Open(domain))
      {
        using (var transactionScope = Transaction.Open())
        {
          var myEntity = new MyEntity();
          transactionScope.Complete();
        }
      }

      using (Session.Open(domain))
      {
        using (var transactionScope = Transaction.Open())
        {
          MyEntity myEntity = Query.All<MyEntity>().FirstOrDefault();
          Console.WriteLine("Sum = " + myEntity.Lines.Sum(l => l.Amount.GetValueOrDefault()));
          transactionScope.Complete();
        }
      }

Updated at 04.05.2010 8:23:59

Yes this helps : but I disagree with your solution.

First problem: myEntity.Lines.Sum(l => l.Amount.GetValueOrDefault()) is of type decimal. So I can't use the ?? operator (decimal can not contains null)

Second problem: This is inconsistent with the behavior of standard LinqToObject Sum()

Sample:

class Test
    {
      public decimal? Amount { get; set; }
    }

I create an empty list of objects and sum it (like previous sample but without DO)

List<Test> emptyList = new List<Test>();
      decimal sum2 = emptyList.Sum(l => l.Amount.GetValueOrDefault());
      Console.WriteLine("Sum (decimal) = " + sum2);

The result is 0.

For me this is a (minor) bug, and you should correct this particular case to get a true complete LINQ implementation. Do you agree?

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