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OccurrentOccurrent

EventStore operations

Layer 0: CloudEvents

Occurrent event store implementations may optionally also implement the EventStoreOperations interface. It provides means to delete a specific event, or an entire event stream. For example:

// Delete an entire event stream
eventStoreOperations.deleteEventStream("streamId");
// Delete a specific event
eventStoreOperations.deleteEvent("cloudEventId", cloudEventSource);
// This will delete all events in stream "myStream" that has a version less than or equal to 19.
eventStoreOperations.delete(streamId("myStream").and(streamVersion(lte(19L))));

These are probably operations that you want to use sparingly. Typically, you never want to remove any events, but there are some cases, such as GDPR or other regulations, that requires the deletion of an event or an entire event stream. You should be aware that there are other ways to solve this though. One way would be to encrypt personal data and throw away the key when the user no longer uses the service. Another would be to store personal data outside the event store.

Another reason for deleting events is if you’re implementing something like “closing the books” or certain types of snapshots, and don’t need the old events anymore.

Another feature provided by EventStoreOperations is the ability to update an event. Again, this is not something you normally want to do, but it can be useful for certain strategies of GDPR compliance. For example maybe you want to remove or update personal data in an event when a users unregisters from your service. Here’s an example:

eventStoreOperations.updateEvent("cloudEventId", cloudEventSource, cloudEvent -> {
    return CloudEventBuilder.v1(cloudEvent).withData(removePersonalDetailsFrom(cloudEvent)).build();
});

updateEvent keeps the values the store owns, whatever event your update function returns. Those values are the event’s position, its DCB tags, its streamId and its streamVersion. The event updateEvent returns has the same values as the stored document.

If you called updateEvent on a MongoDB event store running 0.33.0 or earlier, read repairing events damaged before 0.34.0 under upgrading to 0.34.0.