I have a IB_Cursor, which selects data from selectable SP. It can
happen, that the SP raises a exception. In this case I want to rollback
the transaction. Here's what I want to do:

try
IB_Cursor1.Open;
while not IB_Cursor1.Eof do
begin
IB_Cursor1.Next;
end;
Close;
IB_Transaction1.Commit;
except
begin
IB_Transaction1.Rollback;
raise;
end;
end;

The problem is, that the transaction always commits even when an error
occurs. I have done some debugging and found the following:
The procedure TIB_Dataset.SysFetchNext in IB_Components.pas calls

try
HandleException( Self );
FINALLY
DoCloseOffToEof;
end;

In my case it calls DoCloseOffToEof, which has the code:

procedure DoCloseOffToEof;
begin
FCursorEof := true;
API_CloseCursor;
IB_Transaction.CheckOAT;
ARow.ClearBuffers( rsNone );
SysAfterFetchCursorEof;
FCallbackInitTick := 0;
end;

IB_Transaction.CheckOAT finally commits the transaction. To summaries,
when a IB_Cursor runs into an error, it closes. When it closes, it
commits automatic.
Does anyone knows a way, how to get control over the transaction? As I
mentioned, I want to rollback the transaction when the cursor runs into
an error.

Regards

Guido