[{"id":119,"customfields":[{"value":"Mr","type":"salutation"},{"value":"Google","type":"company"}]}]

db.collection.update({"id":119},[{"$set":{"newRoot":{"$reduce":{"input":"$customfields","initialValue":{"id":"$id"},"in":{"$mergeObjects":["$$value",{"$arrayToObject":[[{"k":"$$this.type","v":"$$this.value"}]]}]}}}}},{"$replaceWith":"$newRoot"}])