Still get error popup even when ApplyUpdates is inside try…except

问题

Solution found, see my comment below

D5, odbc to mysql database

This code:

  with QryCmdPerf do begin
    Close;
    ParamByName('ACCTID').AsInteger:= AcctId;
    ParamByName('FROMDT').AsString:= MySQLDate(FromDt);
    ParamByName('TODT').AsString:= MySQLDate(ToDt);
    Open;
    first;
    try
      edit;
      FieldByName('PnL').AsFloat:= 97979;
      ApplyUpdates;
    except
      close;
    end;
  end;    // with

(specifically the "ApplyUpdates") causes a popup to appear with the text "Update Failed" if the PnL field already has the value 97979, evidently because of this code:

procedure TUpdateSQL.ExecSQL(UpdateKind: TUpdateKind);
begin
  with Query[UpdateKind] do
  begin
    Prepare;
    ExecSQL;
    if RowsAffected <> 1 then DatabaseError(SUpdateFailed);
  end;
end;

in DBTables.pas. Anyway, I want to be able to issue ApplyUpdates, and not have to worry about a popup if it doesn't do any updating. But if "try...except" doesn't work, what will?

TIA

回答1:

You're confusing the dialog displayed by the debugger with a dialog displayed by your program. Please see this article I wrote a few years ago:

Why do I continue getting error messages even after I have written an exception handler?

It describes several ways to avoid the debugger interfering:

Use "advanced breakpoints" to temporarily disable the debugger around the code that throws exceptions.
Configure the debugger to ignore certain exception types. (Read the debugger's message more carefully to see exactly what exception class you're dealing with.)
Configure the debugger not to interrupt on any exceptions.
Turn off integrated debugger entirely.

回答2:

The short answer is, you have to set up an eventhandler for OnUpdateError or no amount of "try...except" blocks will block the popup. The long answer is it appears to be a bug with odbc. The repro is here: http://www.codeupload.com/3919 for anyone who wants to take a look at it. You can skip the MySQL stuff, any odbc database will do.

回答3:

There are two things that can be going wrong here.

Option 1

First, some "very bad code" may be short-circuiting the unwinding of the call stack on exceptions. E.g. ApplyUpdates or one of its child routines may also have a try...except block that calls Application.HandleException directly.

To test this, if you put a breakpoint on QryCmdPerf.Close, do you reach it?
If not, then Application.HandleException (or worse Application.ShowException) has been called directly.

Solving this requires a custom exception handler hooked to the Application.OnException event. You may have to set temporary state to know when this particular exception can be ignored.
Yes it's messy, that why calling Application.HandleException directly, is "very bad code".

Option 2

If you do reach the breakpoint, but the exception is being raised again, then it should be a lot simpler to solve.

The Close method is probably attempting to save any pending changes, so is effectively applying the updates again. Rather than simply closing the data set, call CancelChanges or equivalent.

来源：https://stackoverflow.com/questions/5735719/still-get-error-popup-even-when-applyupdates-is-inside-try-except

标签

Delphi

odbc