Exception when selecting supervisor of employee

I am using Lightspeed 4.0.1600.21511 (nightly 26 sept 2012) on the Northwind database. I try to select the last name of each employee and the employee he reports to:

dataGridView1.DataSource = uow.Employees.Select(e => new
            {
                e.LastName,
                ReportsTo = e.ReportsTo.LastName
            }).ToList();

I get the following exception:

System.Reflection.TargetInvocationException was unhandled
  Message=Exception has been thrown by the target of an invocation.
  Source=mscorlib
  StackTrace:
       at System.RuntimeMethodHandle._InvokeMethodFast(IRuntimeMethodInfo method, Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeType typeOwner)
       at System.RuntimeMethodHandle.InvokeMethodFast(IRuntimeMethodInfo method, Object target, Object[] arguments, Signature sig, MethodAttributes methodAttributes, RuntimeType typeOwner)
       at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks)
       at System.Delegate.DynamicInvokeImpl(Object[] args)
       at System.Delegate.DynamicInvoke(Object[] args)
       at Mindscape.LightSpeed.Linq.Plan.SingleQueryPlan.<>c__DisplayClass31.<Project>b__30(Object[] v)
       at System.Collections.Generic.List`1.ForEach(Action`1 action)
       at Mindscape.LightSpeed.Linq.Plan.SingleQueryPlan.Project(IUnitOfWork unitOfWork, IDataReader reader, IList`1 projectors)
       at Mindscape.LightSpeed.Linq.Plan.SingleQueryPlan.<>c__DisplayClass1d.<ExecuteProject>b__1c()
       at Mindscape.LightSpeed.Linq.Plan.SingleQueryPlan.ChooseProjectImplementation[T](Func`1 native, Func`1 clientSide)
       at Mindscape.LightSpeed.Linq.Plan.SingleQueryPlan.ExecuteProject(IUnitOfWork unitOfWork)
       at Mindscape.LightSpeed.Linq.Plan.SingleQueryPlan.ExecuteImmediate(IUnitOfWork unitOfWork, Type returnType)
       at Mindscape.LightSpeed.Linq.LinqQueryProvider.Execute(Expression expression)
       at Mindscape.LightSpeed.Linq.LinqQueryProvider.System.Linq.IQueryProvider.Execute(Expression expression)
       at Mindscape.LightSpeed.Linq.LinqQuery`1.GetEnumerator()
       at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
       at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
       at Northwind.Form1.button1_Click(Object sender, EventArgs ea) in D:\Projects\Northwind\Northwind\Form1.cs:line 28
       at System.Windows.Forms.Control.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
       at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.ButtonBase.WndProc(Message& m)
       at System.Windows.Forms.Button.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
       at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.Run(Form mainForm)
       at Northwind.Program.Main() in D:\Projects\Northwind\Northwind\Program.cs:line 18
       at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException: System.NullReferenceException
       Message=Object reference not set to an instance of an object.
       Source=Anonymously Hosted DynamicMethods Assembly
       StackTrace:
            at lambda_method(Closure , Employee )
       InnerException: 

This is because ReportsTo is null for some employees. I expect no exception, however, because SQL would return NULL for a similar query. If an exception is still thrown, I would expect it to be a nullreference exception.

Also, the following code does not throw any exception, but simply returns no data:

dataGridView1.DataSource = uow.Employees.Where(e => e.ReportsTo.LastName == "Fuller").Select(e => new
            {
                e.LastName,
                ReportsTo = e.ReportsTo.LastName
            }).ToList();

I expect this to return all employees that report to Fuller, or, if that is not possible, to throw an exception. It currently returns no data without throwing an exception.

Regarding the throwing of the actual exception, thats a fair request and I have added in an update to throw the inner exception where it is available which will cater for the cases where the exception is being fired from performing a client-side projection giving you better insight as you have suggested. This update will be in the next nightly build.

With the queries you are performing though, ReportsTo is a self-join on Employee and this unfortunately is not supported currently by our LINQ provider (see: http://www.mindscapehq.com/documentation/lightspeed/Appendices/LINQ-Support-Limitations for some high level details about what is not supported) so the query being generated for that will most likely be invalid. In general terms though, if we receive an empty set back from SQL then you will receive an empty collection of entities back and not an exception.

Jeremy