'This method is for controlling which database the QuerySet will be
evaluated against if you are using more than one database.
:param alias: The database alias
.. versionadded:: 0.9'

def using(self, alias):

    with switch_db(self._document, alias) as cls:
        collection = cls._get_collection()
    return self._clone_into(self.__class__(self._document, collection))
