DELPHI AREA Forum

I have to write a stupid application that uses a remote MySQL as database. Each instance of this application needs to be notified about changes made by other instances on the database in real time.

Whether I need a middle ware application to manage notifications, or is there an easier solution?

Thank you.

if you use transactions you don't need to notify other clients about changes,
search for transactions in mysql

Ps:don't call my favorite database stupid man

I don't use transaction because I don't need it. Using transactions makes the database operations slower.

As solution, I used a pair of MultiCast TCP server and client in my application to notify other instances when something critical has been changed.

By the way, I called my application stupid, not MySQL.

second solution is,
(Windows Messaging)
,
& third solution is (Creating Shared Memory),{CreateFileMapping &...}

Do mapped files and Windows messages work across network?

No,
these don't work across network.
these are for system wide communicate on a single computer between Applications.
for across network,
I think your solution is good.
what is your problem with your solution?

Actually nothing!

Just wanted to prevent doing something which could be already available as built-in.

Kambiz wrote:I don't use transaction because I don't need it. Using transactions makes the database operations slower.

As solution, I used a pair of MultiCast TCP server and client in my application to notify other instances when something critical has been changed.
.

hmm,would it be much faster to worth using? if so would you share more light on it

When each instance of my program does a database operation, it broadcasts a message across the network with the following information:

• Table Name (actually ID)
• Operation which can be either Insert, Update, or Delete
• Record ID

When an instance receives this kind of message (even the message owner) it broadcasts it as a Windows message to all the open forms. Eventually, each form processes the Windows message to update its current state.

As I already said, I use MultiCast protocol (Indy implementation) to broadcast the message. But notice that MultiCast does not work on a machine without network connection (a socket error occurs).

Here is the actual code in my application:

Code: Select all

// broadcast the message to the application's forms
procedure TDM.LocalBroadcast(const Message: TMessage);
var
  I: Integer;
begin
  for I := 0 to Screen.FormCount - 1 do
    with Screen.Forms[I] do
      if HandleAllocated then
        PostMessage(Handle, Message.Msg, Message.WParam, Message.LParam);
end;

// broadcasts the message accross the network
procedure TDM.NetworkBroadcast(const Message: TMessage);
begin
  if MultiCastServer.Active then { are we connected to a network? }
    MultiCastServer.SendBuffer(Message, SizeOf(Message))
  else
    LocalBroadcast(Message);
end;

// dispatch meesages received from network to the application's forms
procedure TDM.MultiCastClientIPMCastRead(Sender: TObject; AData: TStream;
  ABinding: TIdSocketHandle);
var
  Message: TMessage;
begin
  AData.Position := 0;
  while AData.Read(Message, SizeOf(Message)) = SizeOf(Message) do
    LocalBroadcast(Message);
end;