method finds unit_of_work record and returns it to the caller

def get_one(self, key):
        """ method finds unit_of_work record and returns it to the caller"""
        query = {'_id': ObjectId(key)}
        collection = self.ds.connection(COLLECTION_UNIT_OF_WORK)

        document = collection.find_one(query)
        if document is None:
            msg = 'UOW with ID={0} was not found'.format(key)
            self.logger.warning(msg)
            raise LookupError(msg)
        return UnitOfWork.from_json(document)