$aggregate query cannot be used with $comment or $hint

[ericyhwang]

A query like this:

{
  $aggregate: [
    {$match: {species: 'sheep'}},
    {$count: {$sum: 1}}
  ],
  $comment: 'I am counting sheep'
}

Results in an error message "Cursor methods can't run after collection method $aggregate" coming from:

sharedb-mongo/index.js

Lines 1027 to 1031 in f746c0f

	if (collectionOperationKey && foundCursorMethod) {
	return ShareDbMongo.cursorAndCollectionMethodError(
	collectionOperationKey
	);
	}

The 3.x Mongo driver returns a cursor from db.collection.aggregate() and therefore allows further chaining, but the 2.x driver does not, which is why that check exists. One potential fix that would work with both versions - special-case aggregations to pass a comment/hint in the options when calling .aggregate().