Connection Lost events

maciejmt · Post by **maciejmt** » Tue 13 Jul 2010 15:21

I would like create own procedure of reconnect to MySQL server.

For test, I put:

showmessage('test');

in event OnConnectionLost of TMyConnection (also in AfterDisconnect).

Next, In services, I stopped MySQL service and showmessage doesn't appear.

Why ?

Challenger · Post by **Challenger** » Tue 13 Jul 2010 15:51

Please try to set the LocalFailover property to true.

maciejmt · Post by **maciejmt** » Tue 13 Jul 2010 16:06

Don't working...
I have MyDac 5.80 and D2009.

I click button to connect DB. Next in services stop MySQL.

Code: Select all

procedure TForm1.Button1Click(Sender: TObject);
begin
  myconnection1.Connect;
end;

procedure TForm1.MyConnection1AfterDisconnect(Sender: TObject);
begin
  showmessage('test');
end;

procedure TForm1.MyConnection1ConnectionLost(Sender: TObject;
  Component: TComponent; ConnLostCause: TConnLostCause;
  var RetryMode: TRetryMode);
begin
  showmessage('test');
end;

procedure TForm1.MyConnection1Error(Sender: TObject; E: EDAError;
  var Fail: Boolean);
begin
  showmessage('test');
end;

eduardosic · Post by **eduardosic** » Wed 14 Jul 2010 02:00

Set MyConnection.Options.LocalFailOver := True
and use the OnConnectionLost Event.

maciejmt · Post by **maciejmt** » Wed 14 Jul 2010 05:27

eduardosic wrote:Set MyConnection.Options.LocalFailOver := True
and use the OnConnectionLost Event.

In your work?

1. I set LocalFailOver := True
2.

Code: Select all

procedure TForm1.MyConnection1ConnectionLost(Sender: TObject;
  Component: TComponent; ConnLostCause: TConnLostCause;
  var RetryMode: TRetryMode);
begin
  showmessage('test');
end;

3. connect to DB
4. Stop MySQL service
5. Nothing happened
6. Click button

Code: Select all

  if myconnection1.Connected then
    showmessage('why connected ?');

(dialog appears)
7. MySQL administrator log

C:\Program Files\MySQL\MySQL Server 5.1\bin\mysqld: Forcing close of thread 4 user: 'xx'

C:\Program Files\MySQL\MySQL Server 5.1\bin\mysqld: Forcing close of thread 3 user: 'xx'

C:\Program Files\MySQL\MySQL Server 5.1\bin\mysqld: Forcing close of thread 1 user: 'xx'

8. D2009 + MyDAC v5.80.0.47

eduardosic · Post by **eduardosic** » Wed 14 Jul 2010 05:34

try this.

Put a TMyQuery linked with a TMyConnection and execute this..

Code: Select all

    MyConnection.Connect;
    ShowMessage( 'Please, stop MySQL Server and press OK to continue.' );
    MyQuery.Close;
    MyQuery.SQL.Text := 'Select Version()' ;
    MyQuery.Execute; // Ok on this point. LostConnection is called.. 
    //Lost Connection Happen when yoy try a comunication with server.

remember, you can set RetryMode in onConnectionLost Event

RetryMode := rmReconnectExecute;

Please, see Mydac Demo
C:\Users\Public\Documents\Devart\MyDac for RAD Studio 2007\Demos\Win32\Miscellaneous\FailOver

And Upgrade the Mydac to the Last Version.

Challenger · Post by **Challenger** » Wed 14 Jul 2010 09:07

To eduardosic:
Thanks for the sample.

To maciejmt:
The connection lost will be detected on the first database operation. So you should execute any statement and then this event will be raised.

maciejmt · Post by **maciejmt** » Wed 14 Jul 2010 13:36

thx !

In this case, Showmessage falls into infinity loop.

Code: Select all

procedure TForm1.MyConnection1ConnectionLost(Sender: TObject;
  Component: TComponent; ConnLostCause: TConnLostCause;
  var RetryMode: TRetryMode);
begin
  showmessage('t');
end;

Here is OK, but is throwing exception.
I want use this code in serviceapp.
It will be OK ?

Code: Select all

procedure TForm1.MyConnection1ConnectionLost(Sender: TObject;
  Component: TComponent; ConnLostCause: TConnLostCause;
  var RetryMode: TRetryMode);
begin
  RetryMode := rmRaise;
  //Own procedure of reconnect
end;

RetryMode.rmReconnect is bad, I noticed that application is 'freezing', when stopped MySQL.

Dimon · Post by **Dimon** » Mon 19 Jul 2010 10:27

If your code worked in a desktop application, it should work in a service application as well.