[ChangeStream]

[trappa92]

Brief overview

In ChangeStream definition, we can define filters, but can we also define projections? Ideally, need to have the possibility to pass a list of projections as parameter (like "avars" for filters) and have same mecanism with optional variables via "ifvar"

Thanks

[ujibang]

Hi @trappa92 ,

yes ✅ you can modify the change stream output using pipeline stages including $project, see https://www.mongodb.com/docs/manual/changeStreams/#modify-change-stream-output

And yes ✅, you can use ?avar to pass variables to the change stream, see Passing Variables to Change Stream. Starting with RESTHeart 7.6, the change stream definition can use optional stages, see Optional Stages and Variables with default values

[trappa92]

ah ok so avars containes any variable either for match or for projection?

[ujibang]

Yes, with the qparam ?avars={"foo": "bar}, a stage can use it anywhere as {"$var": "foo"}.

An optional stage can use it as {"$ifvar": [ "foo", {...}].

I thought this was clearly documented. If you have suggestions on how to improve the documentation please send us any feedback.