method finds a single job record and returns it to the caller

def get_by_id(self, process_name, db_id):
        """ method finds a single job record and returns it to the caller"""
        collection_name = self._get_job_collection_name(process_name)
        collection = self.ds.connection(collection_name)
        document = collection.find_one({'_id': ObjectId(db_id)})

        if document is None:
            raise LookupError('MongoDB has no job record in collection {0} for {1}'
                              .format(collection, db_id))
        return Job.from_json(document)