Template
single collection
multiple collections
mgodatagen
update
indexe
explain
Stage
Database
bson
mgodatagen
[{_id:"a",total_count:3},{_id:"b",total_count:2}]
Query
db.collection.aggregate([{"$replaceRoot":{"newRoot":{"$arrayToObject":[[{k:"$_id",v:"$total_count"}]]}}}])
Result