Class RDbNotifier

class RDbNotifier;

Description

Provides notification of database changes to clients.

This is useful for shared databases.

Members

Defined in RDbNotifier:
Cancel(), Close(), EClose, ECommit, ERecover, ERollback, EUnlock, NotifyChange(), NotifyUnlock(), Open(), TEvent

IMPORT_C TInt Open(RDbDatabase &aDatabase);

Description

Opens a DBMS change notifier on a database.

Note that a notifier cannot be opened on a client side database.

Parameters

RDbDatabase &aDatabase The database to be observed.

Return value

TInt KErrNone if successful, otherwise another of the system-wide error codes.

IMPORT_C void Close();

Description

Closes a DBMS change notifier. Any outstanding notification request is automatically cancelled.

Note that this function can be called on a DBMS change notifier that has already been closed.

IMPORT_C void NotifyUnlock(TRequestStatus &aStatus);

Description

Makes an asynchronous request for notification of a database event. All events, including the release of all read locks, are reported.

When a database event occurs, the request completes and the TRequestStatus objectcontains one of the enumerators defined by the TEvent enumeration member.

Alternatively, if an outstanding request is cancelled by a call to the Cancel() member function of this class, then the request completes with KErrCancel.

Only one notification request can be outstanding on this notifier at any one time.

Note that if further database events occur while a client is handling a request completion, the notifier records the most significant database event and this is signalled as soon as the client issues the next NotifyUnlock() or NotifyChange() request.

Parameters

TRequestStatus &aStatus The request status object. If the request is cancelled, this is set to KErrCancel. If the request completes normally, this is set to one of the enumerator values defined by the TEvent enumeration member.

IMPORT_C void NotifyChange(TRequestStatus &aStatus);

Description

Makes an asynchronous request for notification of changes to the database.

All events which indicate a change to the database are reported; in practice, this means all database events except RDbNotifier::EUnlock.

When a change event occurs, the request completes and the TRequestStatus object contains one of the appropriate enumerators defined by the TEvent enumeration member.

Alternatively, if an outstanding request is cancelled by a call to the Cancel() member function of this class, then the request completes with KErrCancel.

Only one notification request can be outstanding on this notifier at any one time.

Note that if further database events occur while a client is handling a request completion, the notifier records the most significant database event and this is signalled as soon as the client issues the next NotifyUnlock() or NotifyChange() request.

Parameters

TRequestStatus &aStatus The request status object. If the request is cancelled, this is set to KErrCancel. If the request completes normally, this is set to one of the enumerator values defined by the TEvent enumeration member.

IMPORT_C void Cancel();

Description

Cancels any outstanding notification request to this DBMS notifier.

The outstanding request completes with a KErrCancel.

TEvent

Description

Defines the events which may be reported by a DBMS change notifier through this RDbNotifier object.

Each enumerator corresponds to a distinct event type.

The changes are reported through a TRequestStatus object when an outstanding notification request completes.

Notes

If further database events occur while a client is handling the completion of a previous event, the notifier remembers the most significant event. The order of importance is:

ERecover > ERollback > ECommit

where the symbol > means "is more important than"

EClose The database has been closed. EUnlock All read locks have been removed. ECommit A transaction has been committed. ERollback A transaction has been rolled back ERecover The database has been recovered