Mongodb Stitch realtime watch - mongodb

Question

What I intend to achieve is some sort of "live query" functionality.
So far I've tried using the "watch" method. According to the documentation:
You can open a stream of changes that match a filter by calling
collection.watch(delegate:) with a $match expression as the argument.
Whenever the watched collection changes and the ChangeEvent matches
the provided $match expression, the stream’s event handler fires with
the ChangeEvent object as its only argument
Passing the doc ids as an array works perfectly, but passing a query doesn't work:
this.stitch.db.collection<Queue>('queues')
.watch({
hospitalId: this.activehospitalid
}));
I've also tried this:
this.stitch.db.collection<Queue>('queues')
.watch({
$match: {
hospitalId: this.activehospitalid
}
},
));
Which throws an error on the console "StitchServiceError: mongodb watch: filter is invalid (unknown top level operator: $match)". The intention is watch all documents where the field "hospitalId" matches the provided value, or to effectively pass a query filter to the watch() method.

Answer 1

After a long search I found that it's possible to filter, but the query needs to be formatted differently
this.stitch.db.collection<Queue>('queues')
.watch({
$or: [
{
"fullDocument.hospitalId": this.activehospitalid
}
]
},
));
For anyone else who might need this, please note the important fullDocument part of the query. I havent found much documentation relating to this, but I hope it helps