NOTIFY/LISTEN in Postgresql

[binfch]

Hi there

How can I use the NOTIFY/LISTEN interprocess communication mechanism in postgresql?

See http://www.postgresql.org/docs/9.1/stat ... otify.html

Thanks & cheers,
Peter

[ROD]

Hi

It is very easy. There is a special component for this - TPgAlerter.
With the help of its methods/properties/events the PostgreSQL NOTIFY/LISTEN gear is realized.
So, for example, a notification is sent by the procedure SendEvent(const MessageName: string; MessageText: string);
You can find more details in the context help of the TPgAlerter component.

Also, if you have bought PgDAC, you must have demo projects:
...\Demos\Win32\PgDacDemo\PgDacDemo.dpr
where you can see Alerter in action, watching the sources in parallel

[binfch]

Thanks for the info!

Just for your Information.

-> In my Lazarus/Ubuntu IDE the component "TPgAlerter" is not shown on the component bar/panel (all the other components are well there!).

Thanks & cheers,
P.

[binfch]

Hi there

I am unable to manually free the PgAlerter component in Lazarus/Ubuntu. The same code works fine under Delphi7. Here's my code:

Code: Select all

unit AlerterEventsLib; 

interface

uses
  Classes, SysUtils, DAAlerter, PgAlerter, DB, DBAccess, PgAccess;

type
  TAlerterEvents = class
  private
    PgConnection: TPgConnection;
    PgAlerter: TPgAlerter;
    procedure AlerterEvent(Sender: TObject; const EventName: AnsiString; PID: LongInt; const EventMessage: AnsiString);
  public
    constructor Create(const Channel: AnsiString);
    destructor Destroy;
  end;

implementation

uses
  Globals;

procedure TAlerterEvents.AlerterEvent(Sender: TObject; const EventName: AnsiString; PID: LongInt; const EventMessage: AnsiString);
begin
  WriteLn('Received Event:' + EventName);
end;

constructor TAlerterEvents.Create(const Channel: AnsiString);
begin
  PgConnection := TPgConnection.Create(nil);
  with PgConnection do begin
    Server := ConfigRecord.DatabaseServerIp;
    Port := ConfigRecord.DatabaseServerPort;
    Database := ConfigRecord.DatabaseName;
    Schema := ConfigRecord.DatabaseShema;
    Username := ConfigRecord.DatabaseUser;
    Password := ConfigRecord.DatabasePassword;
  end;

  try
    PgConnection.Connected := True;
    PgAlerter := TPgAlerter.Create(nil);
    PgAlerter.OnEvent := @AlerterEvent;
    with PgAlerter do begin
      AutoRegister := False;
      Connection := PgConnection;
      Events := Channel;
      Active := True;
    end;
  except
    WriteLn('Error Creating PgAlerter');
  end;
end;

destructor TAlerterEvents.Destroy;
begin
WriteLn('Start Destroy PgAlerter');
  PgAlerter.Active := False;
  PgAlerter.Free;
WriteLn('Done');       //<<<<< NEVER COMES UNTIL HERE

WriteLn('Start Destroy PgConnection');
  PgConnection.Connected := False;
  PgConnection.Free;
WriteLn('Done');
end;

end.

Thanks & cheers,
Peter

[ROD]

Hi

That's right, there is no such component for Linux.
We will check the workability of your code.

[binfch]

Hi there

Any news on this?

Thanks & cheers,
P.

[AlexP]

hello,

Presently, TPgAlerter works only on Windows platform, we will try to support PgAlerter in Unix platforms in the next versions

[binfch]

Hi there

Thx for the answer.

I am actually already using TPgAlerter quiet extensively in my Linux/FPC application (development stage). It seems to work just fine so far except that I can not free it correctly.

It would be a shame if I had to change my code again -> Can you give me a approximate date for the next release? If this is not too far I might be able to wait...

Thanks & cheers,
Peter

[AlexP]

hello,

The new release of our products with support of the new two features, Data Encryption and Data Type Mapping, has just come out. Therefore the next release is expected not earlier then in a month

[binfch]

Hi there

Is there any news on this resp. availability of the PgAlerter component for Lazarus/Ubuntu?

Thanks & cheers,
P.

[AlexP]

hello,

We are still working on this problem.
We will notify you as soon as we have any results.

[binfch]

Hi there

Is there any workaround available yet?
I am stuck with this issue for 3 months now! I need a working TPgAlerter for Linux.

Thanks & cheers,
P.

[binfch]

Hi there

Can I assume that no answer = Good answer?

Comon guys you must be able to give some kind of timeline here! I am a paying customer and I am not requesting a new feature. All I expect is that an existing feature gets fixed (Since 4th of June actually)!

Thx & cheers,
Peter

[ZEuS]

The working TPgAlerter component for Linux is the new feature of PgDAC, not just a fix of an existing feature.
TPgAlerter was never supported on Linux, because it widely uses such specific Windows mechanisms as messages and critical sections, the implementation of which in FPC is not good enough.
At the moment we are trying to adapt the TPgAleter component for Linux, and we will notify you when we have any results.

[ZEuS]

We have adapted TPgAlerter for Linux. This component will be included in the next PgDAC build.