'Perform an atomic update on the fields of the first document
matched by the query.
:param upsert: insert if document doesn\'t exist (default ``False``)
:param write_concern: Extra keyword arguments are passed down which
will be used as options for the resultant
``getLastError`` command.  For example,
``save(..., write_concern={w: 2, fsync: True}, ...)`` will
wait until at least two servers have recorded the write and
will force an fsync on the primary server.
:param update: Django-style update keyword arguments
.. versionadded:: 0.2'

def update_one(self, upsert=False, write_concern=None, **update):

    return self.update(upsert=upsert, multi=False, write_concern=write_concern, **update)
