Hello,

We are migrating our application to DataObjects 4.0.5 and I've a problem with abstract classes: I'm getting NullReference exceptions when trying to use an object with it's abstract base class.

Am I doing something wrong?

Persistent classes :

[HierarchyRoot]
  public abstract class Trigger : Entity
  {
    [Field, Key]
    public long Id { get; private set; }

    public abstract string ToText();
  }

  public class SimpleTrigger : Trigger
  {
    [Field]
    public TimeSpan Delay { get; set; }

    public override string ToText()
    {
      return Delay.ToString();
    }
  }

Code (without domain build)

using (Session.Open(domain))
      using(TransactionScope transactionScope = Transaction.Open())
      {
        new SimpleTrigger { Delay = TimeSpan.FromSeconds(1.0) };
        transactionScope.Complete();
      }

      using (Session.Open(domain))
      using (TransactionScope transactionScope = Transaction.Open())
      {
        SimpleTrigger myTrigger = Query<SimpleTrigger>.All.First<SimpleTrigger>();
        Console.WriteLine(myTrigger.ToText()); // working as expected
        transactionScope.Complete();
      }

      using (Session.Open(domain))
      using (TransactionScope transactionScope = Transaction.Open())
      {
        Trigger myTrigger = Query<Trigger>.All.First<Trigger>();
        Console.WriteLine(myTrigger.ToText()); // NullReferenceException
        transactionScope.Complete();
      }

Exception below :

System.NullReferenceException was unhandled
  Message="La référence d'objet n'est pas définie à une instance d'un objet."
  Source="Xtensive.Core"
  StackTrace:
       à Xtensive.Core.Tuples.Tuple.GetValueOrDefault[T](Int32 fieldIndex)
       à Xtensive.Storage.Internals.DefaultFieldAccessor`1.GetValue(Persistent obj, FieldInfo field)
       à Xtensive.Storage.Persistent.GetFieldValue[T](FieldInfo field)
       à Xtensive.Storage.Persistent.GetFieldValue[T](String fieldName)
       à TestDO4.SimpleTrigger.get_Delay()
       à TestDO4.Program.Main(String[] args) dans Visual Studio 2008\Projects\TestDO4\TestDO4\Program.cs:ligne 35
       à System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args)
       à System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       à Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       à System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       à System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       à System.Threading.ThreadHelper.ThreadStart()
  InnerException:

Regards,

Updated at 11.09.2009 13:37:01

After some more investigation, this problem occurs also with virtual methods.

Class not abstract, but with an overridden virtual method.

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

    public virtual string ToText()
    {
      return null;
    }
  }

  public class SimpleTrigger : Trigger
  {
    [Field]
    public TimeSpan Delay { get; set; }

    public override string ToText()
    {
      return Delay.ToString();
    }
  }

When calling Trigger.ToText() I get the same null reference exception on Delay.

Regards,

Updated at 11.09.2009 14:27:38

Thanks for your really fast answer: I'll use your work around, it is much better than mine.

Regards,

This thread was imported from our support forum. The original discussion may contain more detailed answer.