'add' in cloudsearch equals to 'upsert' in mongo

[hokuma]

add operation in cloudsearch is upsert operation, that means always overwriting a document.
update with upsert option is more suitable than insert.

See:
https://docs.mongodb.com/manual/reference/method/db.collection.update/

[oisinmulvihill]

That looks ok, thanks for the contribution.