My express app streams results from a aggregate directly to the client, something like this (much simplified):
.aggregate([
{$match: query},
....
])
.stream({transform: doc_to_ndjson})
.on('error', err => next(createError(status, err)))
.pipe(res.type('text/plain'));
The important part here is that results are streamed, unless the aggregation raises an error, in which case the error message is send to the client.
The mongo-node documentation recommends that stream is replaced with transformStream for the next release, without giving much detail on what has changed. I tried this on my app and it seems to work initially, however I noticed that it no longer raises the error events. In case there is an error, I just get an empty 200 now. Is this expected? How should I handle mongo errors icw/ transformStream ?