Template
single collection
multiple collections
mgodatagen
update
indexe
explain
Stage
Database
bson
mgodatagen
[{"_id":1,"field":"non empty"},{"_id":2,"field":""},{"_id":3,"field":null},{"_id":4}]
Query
db.collection.find({"$expr":{$ne:[{$ifNull:["$field",""]},""]}})
Result