TFBEventMonitor: what changed
Revision 0 to 1. Removed lines have a minus sign; added lines have a plus sign.
Title: TFBEventMonitor
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| 1 | + | **TFBEventMonitor**  in the FBEventMonitor unit is used to monitor named events sent from the [[Firebird]] database server. Events are typically generated by triggers on certain database operations. | |
| 2 | + | ||
| 3 | + | Using events means you can avoid regularly polling the database for status changes and can be useful in cases of high load. | |
| 4 | + | ||
| 5 | + | ## Example | |
| 6 | + | ||
| 7 | + | Updating a memo with events received. Monitoring events E1 through E7. | |
| 8 | + | ||
| 9 | + | ``` pascal | |
| 10 | + | procedure TForm1.StartMonitor; | |
| 11 | + | begin | |
| 12 | + | EventsM:=TFBEventMonitor.create(Self); | |
| 13 | + | EventsM.Connection:=IBConnection1; | |
| 14 | + | EventsM.Events.CommaText:='"E1",E2,E3,E4,"E5","E6","E7"'; //quotes are ignored | |
| 15 | + | EventsM.OnEventAlert:=OnFBEvent; | |
| 16 | + | EventsM.RegisterEvents; // will activate IBConnection1 if not connected | |
| 17 | + | end; | |
| 18 | + | ||
| 19 | + | procedure TForm1.StopMonitor; | |
| 20 | + | begin | |
| 21 | + | EventsM.UnRegisterEvents; | |
| 22 | + | EventsM.Free; | |
| 23 | + | end; | |
| 24 | + | ||
| 25 | + | procedure TForm1.OnFBEvent(Sender: TObject; EventName: string; | |
| 26 | + | EventCount: longint; var CancelAlerts: boolean); | |
| 27 | + | begin | |
| 28 | + | Memo1.Lines.Add(EventName+' occurred '+IntToStr(EventCount)+' times.'); | |
| 29 | + | end; | |
| 30 | + | ``` | |
| 31 | + | ||
| 32 | + | The event monitor stops monitoring when the linked TIBConnection is disconnected and will not restart automatically. Use the TIBConnection.AfterConnect and TIBConnection.BeforeDisconnect event handlers to start and stop the monitoring automatically. | |
| 33 | + | ||
| 34 | + | The database server sends events to all connections registered for these events except for those created by the connection itself. Events are sent after a transaction is committed. Rolling back a transaction will cancel all events created in that transaction. fbeventstest.pp in the fcl packages/fcl-db/examples/ directory is a test/demo program that creates a stored procedure to send an event with an arbitrary name and uses a second connection to monitor the events sent. | |
| 35 | + | ||
| 36 | + | > **Warning:** TFBEventMonitor creates a thread to monitor incoming events. On Unix include cthreads or any other thread manager. | |
| 37 | + | ||
| 38 | + | ## See also | |
| 39 | + | ||
| 40 | + | - [[Firebird|Using Firebird with FPC/Lazarus sqldb.]] | |
| 41 | + | - Firebird documentation/readme files on events | |
| 42 | + | - [Presentation on Firebird events](http://www.firebirdsql.org/file/documentation/papers_presentations/Power_Firebird_events.pdf) | |
| 43 | + | ||
| 44 | + | --- | |
| 45 | + | *From the Free Pascal wiki, page "TFBEventMonitor", as it stood on 2020-03-01 after a change by Trev, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).* |