onEventMissing handling and callback

[OrH]

Hey,

When handling missing events using onEventMissing, the callback is not called which can cause issues with message acking/rejecting, is this correct? If yes, is this by design or can be extended to call the callback after handling the missing events?

Thanks!

[OrH]

I think I might have found my answer - https://github.com/adrai/node-cqrs-eventdenormalizer/blob/master/lib/revisionGuard.js#L218 After handling with the events with revision lower than the revision in the event, it should find the current event that caused the onEventMissing to trigger, and continue with it, is that correct?

[adrai]

Yes, there is no callback for it... it's designed like that. But there should not be any bigger issues with message acking/rejecting...

you should do something like this: pseudo code:

denormalizer.onEventMissing(function (info, evt) {
  // i.e. ignore when already replaying the whole readmodel...
  if (isInReplayMode) return;

  // grab the missing events, depending from info values...
  const aggregateRevision = info.aggregateRevision;
  const guardRevision = info.guardRevision || 1;
  const aggregateId = info.aggregateId;
  const aggregate = info.aggregate;
  const context = info.context;
  const concatenatedId = context + aggregate + aggregateId;

  const missReq = missingRequests[concatenatedId];
  if (missReq && missReq <= aggregateRevision) {
    console.warn('Missing events for "' + context + ':' + aggregate + ':' + aggregateId + '" already requested ==> skip!');
    return;
  }

  // for the above check...
  missingRequests[concatenatedId] = aggregateRevision;

  // and call handle...
  denormalizer.handle(missingEvent, function (err) {
    if (err) { console.log(err); }
  });

  console.log('Start replaying missing events for aggregate "' + context + ':' + aggregate + ':' + aggregateId + '" from revision "' + guardRevision + '"');
});

[OrH]

Hey Adrai, thanks for the quick response! I'll try it 👍 I just didn't understand what is the missingRequests for, is this for if another event will arrive with a smaller revision the the one triggered the onEventMissing?

[adrai]

the main task of it is to detect if an event is missed for some reason... transport problem, denormalizer crashed during denormalization, etc...

[OrH]

Got it. Thanks @adrai !