[{"network_type":"ex","rack":[{"xxxx":{"asn":111111,"nodes":{"business":["sk550abcc1eb01.abc.com","sk550abcc1eb10.abc.com","sk550abcc1eb19.abc.com","sk550abcc1eb28.abc.com"]},"region":"ex-01","zone":"01a"}}]}]

db.collection.update({},[{$set:{rack:{$map:{input:"$rack",in:{$mergeObjects:[{"details":"$$this.xxxx"},"$$this"]}}}}},{$unset:"rack.xxxx"}])