def METHOD_NAME(self, session, attr_id, ftrack_ids):
    output = query_custom_attributes(
        session, [attr_id], ftrack_ids, True
    )
    mongo_id_by_ftrack_id = {}
    for item in output:
        mongo_id = item["value"]
        if not mongo_id:
            continue
        ftrack_id = item["entity_id"]
        mongo_id_by_ftrack_id[ftrack_id] = mongo_id
    return mongo_id_by_ftrack_id