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

db.collection.aggregate([{"$match":{"id":119}},{"$set":{"customfields":{"$arrayToObject":{"$map":{"input":"$customfields","as":"cf","in":{"k":"$$cf.type","v":"$$cf.value"}}}}}},{"$replaceRoot":{"newRoot":{"$mergeObjects":["$$ROOT","$customfields"]}}},{"$unset":"customfields"},{"$merge":{"into":"collection","on":"id"}}])