|Oracle® Objects for OLE Developer's Guide
11g Release 2 (11.2) for Microsoft Windows
Part Number E12245-01
Adds a subscription to the
orasubscriptions.Add Name, DbeventsHdl, Ctx
The arguments for the method are:
||The database event of interest. The appropriate event trigger and AQ queue must be set up prior to this.
||The database event handler. An
||Context-specific information that the application wants passed to the
To register for subscription of a database event, the name identifying the subscription of interest and the name of the
dbevent handler that handles the event must be passed in when the
Add method is called. The queues and event triggers necessary to support the database event must be set up before the subscriptions can be fired.
dbevent handler should be an automation object that implements the
NotifyDBEvents method is invoked by Oracle Objects for OLE when database events of interest are fired.
For more detailed information about setting up the queues and triggers for Oracle Database events, see to Triggers on System Events and User Events in Oracle Database Concepts.
The syntax of the method is:
Public Function NotifyDBEvents(ByVal Ctx As Variant, ByVal Payload As Variant
The variants for the method are:
||Passed into the
||The payload for this notification.
Database events are fired by setting up event trigger and queues.
Example: Registering an Application for Notification of Database Events
In the following example, an application subscribes for notification of database logon events (such as all logons to the database). When a user logs on to the database, the
NotifyDBEvents method of the
DBEventsHdlr that was passed in at the time of subscription is invoked. The context-sensitive information and the event-specific information are passed into the
DBEventsHdlr in this example is
DBEventCls, which is defined later.
The main application:
' First instantiate the dbevent handler. The dbevent notification ' will fire the NotifyDBEvents on the callback handler. Public DBEventsHdlr As New DBEventCls Private Sub Form_Load() Dim gOraSession As Object Dim gOraSubscriptions As OraSubscriptions Dim gOraDatabase As OraDatabase 'Create the OraSession Object Set gOraSession = CreateObject("OracleInProcServer.XOraSession") 'Create the OraDatabase Object by opening a connection to Oracle. Set gOraDatabase = gOraSession.DbOpenDatabase ("ora90.us.oracle.com", "pubsub/pubsub", ORADB_ENLIST_FOR_CALLBACK) Set gOraSubscriptions = gOraDatabase.Subscriptions gOraSubscriptions.Add "PUBSUB.LOGON:ADMIN", DBEventsHdlr, gOraDatabase gOraSubscriptions(0).Register MsgBox "OK" End Sub
The database event handler class that defines the
Public countofMsgs as integer Public Function NotifyDBEvents(Ctx As Variant, Payload As Variant ) On error goto NotifyMeErr MsgBox "Retrieved payload " + Payload ' do something - here the subscription is unregistered after ' receiving 3 notifications countofMsgs = countofMsgs + 1 If countofMsgs > 3 Then Ctx.Subscriptions(0).UnRegister End If Exit Sub NotifyMeErr: Call RaiseError(MyUnhandledError, "newcallback:NotifyMe Method") End Sub
"Database Events" for a complete discussion of the concepts involved in this example
Triggers on System Events and User Events in Oracle Database Concepts for detailed information about setting up the queues and triggers for Oracle Database Events