Thanks! In my real application I want to be able to update a sub-array of the document, like this: collection['some_identifier']['items'][3] = 123. Just setting the value for the key (e.g. overwriting the whole document) seems wasteful since I only want to update a portion of it. With MongoDB it's easy to set sub-data so I guess I'm looking for something where it's as easy but without the downsides.