Kuzzle / how to dispatch event only to subscribed user based on a condition

Question

I'm looking for the best approach to dispatch event to subscribed user based on user info condition.

My use case is:

• user with username = "A" subscribed to doc_created events (https://docs.kuzzle.io/sdk/js/7/controllers/realtime/subscribe/#subscribe)
• user with username = "B" also subscribed to doc_created events (same index + collection)
• Then I have a doc created with a field : forUser = "A"
• My goal is to dispatch the "doc_created" (https://docs.kuzzle.io/core/2/framework/events/generic-document/#generic-document-afterwrite) event only to user with username = "A" and drop the message that is sent to the user with username = "B".

Any advice for this use case?

Answer 1

In order to achieve that, the best way would be to inject users subscriptions with a filter on the documents author metadata.

This injection could be done with a pipe on the realtime:beforeSubscribe event.

You need to modify the filters to include a clause on the document author but also keep the original filters with the and operator. You can get inspiration with this example:

app.pipe.register('realtime:beforeSubscribe', request => {
  request.input.body = {
    and: [
      {
        equals: { '_kuzzle_info.createdAt': request.context.user._id }
      },
      request.input.body
    ]
  };

  return request;
});