Exceptions using Lynq queries in a lightswitch button _execute method.

Question

I'm not sure if this is a LightSwitch or a ComponentOne FlexGrid issue so I'm reporting it on both sites.The following _Execute fails if I use the Dispatch with the Lynq query.
private readonly List<Int32> DebitGPAccountRowindices = new List<int>();
partial void SetAllDebitGPAccounts_Execute()
Dispatchers.Main.BeginInvoke
() =>
//Modify the Column Values for collected Row Indices
foreach (var t in DebitGPAccountRowindices)
var MyAcct = from g in this.DataWorkspace.SPDCData.GPAccounts
where ( g.ConceptID == ConceptId
&& g.ApplicationId == 1
&& g.GLDepartment == Department
&& g.GLAccount == TargetGLAccount)
select g;
var MyRowToUpdate = MyAcct.FirstOrDefault();
if (MyRowToUpdate != null)
_flex[t, "DebitGLAccountId"] = GLAccountId;
If I use the dispatch I get a System.InvalidOperationException at the line -->var MyRowToUpdate = MyAcct.FirstOrDefault();
{System.InvalidOperationException: It is not valid to execute the operation on the current thread.
   at Microsoft.LightSwitch.Threading.DispatcherExtensions.VerifyAccess(IDispatcher dispatcher)
   at Microsoft.LightSwitch.DataServiceQueryable.ScalarImpl[T](IDataServiceQueryable`1 source, Int32 takeCount, Func`2 scalarFunction)
   at Microsoft.LightSwitch.DataServiceQueryable.FirstOrDefault[TSource](IDataServiceQueryable`1 source)
   at LightSwitchApplication.DepartmentFeeFlexibleGrid.<SetAllDebitGPAccounts_Execute>b__1()
   at Microsoft.LightSwitch.Threading.ClientGenerated.Internal.MainDispatcher.<>c__DisplayClass2.<BeginInvoke>b__0()}
If I remove the dispatch and just run it I get the following error at the line -->_flex[t, "DebitGLAccountId"] = GLAccountId;"
{System.UnauthorizedAccessException: Invalid cross-thread access.
   at MS.Internal.XcpImports.CheckThread()
   at System.Windows.DependencyObject.GetValueInternal(DependencyProperty dp)
   at System.Windows.FrameworkElement.GetValueInternal(DependencyProperty dp)
   at System.Windows.DependencyObject.GetValue(DependencyProperty dp)
   at C1.Silverlight.FlexGrid.C1FlexGrid.get_ShowErrors()
   at C1.Silverlight.FlexGrid.Row.UpdateErrors()
   at C1.Silverlight.FlexGrid.Row.InvalidateCell(Column c)
   at C1.Silverlight.FlexGrid.Row.SetData(Column col, Object value)
   at C1.Silverlight.FlexGrid.Row.set_Item(Column col, Object value)
   at C1.Silverlight.FlexGrid.GridPanel.set_Item(Int32 row, Column col, Object value)
   at C1.Silverlight.FlexGrid.C1FlexGrid.set_Item(Int32 row, Column col, Object value)
   at C1.Silverlight.FlexGrid.C1FlexGrid.set_Item(Int32 row, String colName, Object value)
   at LightSwitchApplication.DepartmentFeeFlexibleGrid.SetAllDebitGPAccounts_Execute()
   at LightSwitchApplication.DepartmentFeeFlexibleGrid.DetailsClass.MethodSetProperties._SetAllDebitGPAccounts_InvokeMethod(DetailsClass d, ReadOnlyCollection`1 args)
   at Microsoft.LightSwitch.Details.Framework.Internal.BusinessMethodImplementation`2.<TryInvokeMethod>b__5()
   at Microsoft.LightSwitch.Utilities.Internal.UserCodeHelper.CallUserCode(Type sourceType, String methodName, String instance, String operation, ILoggingContext context, Action action, String additionalText, Func`1 getCompletedMessage, Boolean tryHandleException,
Boolean swallowException, Exception& exception)}
Does anyone have an idea what is happening here?
Scott Mitchell

Answer 1

Your database transaction should not span two buttons. The two buttons will be called on separate requests -- that is, separate calls to the server -- and you'll have a database connection dangling out there, potentially locking other people out of certain tables/rows until the user clicks the right button.
Note also that there is a commit() method in the JDBC API.
You might want to spend some time studying some example applications.