How to Handle EDatabaseError from MySQL?
lazarus / 8-Other

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anderson5420 · 2008-05-31 17:48

OK, new to Lazarus, love it so far!

I more or less duplicated the little program tryMySQL from the
MYSQLDatabases article in the Wiki that uses the SQLdb components -
WAY slick, so much better than where I left off from Delphi (Delphi 4,
about 10 years ago, but it is like riding a bike!).  System is XP
under Parallels 3 on a MacBook.  MySQL is version 5.0.  The compiiled
program runs great until I try to open an invalid SQL command either
by accident or on purpose.  Lazarus then goes into debugging mode with
"Project raised an EDatabaseError."  This is not unexpected of course.
In the MySQL command line tool, it just returns the nature of the
error and lets you try again. So I am wondering how to handle this
error and let the user try again in my faux tryMySQL program.

Here is what I have in the code for the event handler for the button
that opens the SQL command:

Code: [Select]

procedure TMainForm.ExecuteQueryButtonClick(Sender: TObject);
begin
  SQLQuery1.SQL.Text := CommandEdit.Text;
  SQLQuery1.ParseSQL := false;
  SQLQuery1.ReadOnly := true;
  try
    SQLQuery1.Open;
  except
     ShowString('Unable to execute SQL command');
   end;
end;



I thought maybe the try...except would handle the error, but evidently
it only handles Lazarus errors, not the MySQL errors.

Have Googled this, tried the Search here, am coming up empty.  Anyway,
would appreciate it if somebody could help me figure out how to handle
the EDatabaseError so that the user can just go on and try again.

Thanks!

Pat Anderson

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anderson5420 · 2008-06-01 16:01

Guess I'm talking to myself!  Did a bit more searching on the Wiki and
came up with this. Ought to work but doesn't, still gives
EDatabaseError message and goes into debbugging mode.  Why doesn't
this work?

Code: [Select]
procedure TMainForm.ExecuteQueryButtonClick(Sender: TObject);
begin
     SQLQuery1.SQL.Text := CommandEdit.Text;
     try
        SQLQuery1.Open;
     except
           on E : EDatabaseError do
              ShowString('DB ERROR:' + ' ' + E.ClassName + ' ' +
E.Message);
           on E : Exception do
              ShowString('ERROR:' + ' ' + E.ClassName + ' ' +
E.Message);
     end;
end;

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anderson5420 · 2008-06-02 12:24

Well, interesting thing...I did a build with the error handling on the
SQLQuery1.Open as above. The program handles the error fine outside
the IDE, it just logs the error and lets the user keep going, but
inside the IDE the error causes Lazarus to suspend normal execution of
the program and go into the debugger. Is this behavior a bug in the
IDE?  I would think that if a program actually is handing an error
properly, the IDE should not suspend the program. I wasted a fair
amount of time trying to research why code that should work did not
seem to be working, when all along apparently it was working fine...

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Leledumbo · 2008-06-03 06:22

Another debugger problem... try replacing the debugger (e.g. download
your own).