exists(foo={"$gt": 12})

        Returns ``True`` if a matching file exists, ``False``
        otherwise. Calls to :meth:`exists` will not automatically
        create appropriate indexes; application developers should be
        sure to create indexes if needed and as appropriate.

        :Parameters:
          - `document_or_id` (optional): query document, or _id of the
            document to check for
          - `session` (optional): a
            :class:`~pymongo.client_session.ClientSession`
          - `**kwargs` (optional): keyword arguments are used as a
            query document, if they're present.

        .. versionchanged:: 3.6
           Added ``session`` parameter.
        r.