Find a single document by id

        :param str _id: BSON string repreentation of the Id
        :return: a signle object
        :rtype: dict

def find_one_by_id(self, _id):
        """
        Find a single document by id

        :param str _id: BSON string repreentation of the Id
        :return: a signle object
        :rtype: dict

        """
        document = (yield self.collection.find_one({"_id": ObjectId(_id)}))
        raise Return(self._obj_cursor_to_dictionary(document))