Template
single collection
multiple collections
mgodatagen
update
indexe
explain
Stage
Database
bson
mgodatagen
[{"_id":"A","userId":"B","selectedUsers":["C","D"]}]
Query
db.collection.aggregate([{$match:{userId:"B"}},{$project:{_id:0,result:{$map:{input:["E","C"],in:{$in:["$$this","$selectedUsers"]}}}}}])
Result