support for change streams

[adrian-gierakowski]

would be nice to have equivalents of db.watch and db.collection.watch

Looking at spec it seems like those methods are implemented by client libraries using aggregation under the hood (with first pipeline stage being $changeStream). Based on this, I guess it should be relatively easy to add first class support for changes streams in this library. Do you foresee any difficulties?

[TomMD]

I'd love to hear the maintainer's thoughts on supporting change streams and belief on scope of effort if it needs to be an external contribution.

[VictorDenisov]

The driver has support of commands. Aggregation pipelines are just a command. So if anyone needs streams they can be implemented even outside of the driver. If the code turns out to be generic enough we'll be happy to merge it to the driver's codebase.