Template
single collection
multiple collections
mgodatagen
update
indexe
explain
Stage
Database
bson
mgodatagen
[{"_id":ObjectId("123456789101112131415161"),"slug":1},{"_id":ObjectId("123456789101112131415162"),"slug":1}]
Query
db.collection.aggregate([{$set:{"slug":{"$toString":"$_id"}}}])
Result