Template
single collection
multiple collections
mgodatagen
update
indexe
explain
Stage
Database
bson
mgodatagen
[{_id:1,tokens:[1,2,3]},{_id:2,tokens:[4,5,6]}]
Query
db.collection.aggregate([{$unwind:"$tokens"},{$group:{_id:null,tokens:{"$push":"$tokens"}},},{$project:{tokens:1}}])
Result