Template
single collection
multiple collections
mgodatagen
update
indexe
explain
Stage
Database
bson
mgodatagen
[{_id:1,"tag":{"tagName":0.10534846782684326}},{_id:2,"tag":{".tagName":0.10534846782684326}}]
Query
db.collection.find({$expr:{$ifNull:[{$getField:{field:".tagName",input:"$tag"}},false]}})
Result