Template
single collection
multiple collections
mgodatagen
update
indexe
explain
Stage
Database
bson
mgodatagen
[{"_id":"123","test":{"a":1,"b":1}},{"_id":"456","test":{"a":1}},{"_id":"789","test":{"a":1,"b":1,"c":1}}]
Query
db.collection.find({$expr:{$gt:[{"$size":{"$objectToArray":"$test"}},1]}})
Result