[{"my_object":{"1":{"seq":"1","time":"xyz"},"2":{"seq":"2","time":"abc","sub_aray":{"0":{"value":10},"1":{"value":10},"2":{"value":-10}}}}}]

db.collection.aggregate([{"$project":{"my_object":{"$map":{input:{"$objectToArray":"$my_object"},as:"obj",in:{seq:"$$obj.v.seq",sub_array:{$sum:{$map:{input:{"$objectToArray":"$$obj.v.sub_aray"},as:"sub",in:"$$sub.v.value"}}}}}}}},{"$unwind":"$my_object"},{"$replaceRoot":{"newRoot":"$my_object"}}])