@Alexander-Anderson your are right, updates:

show collections
db.objects.find( { "_key" : "username:uid" } )
db.objects.find( { "_key" : "group:administrators:members" } )
db.objects.update( { "_id" : ObjectId("54022b7f60757d4944a05931") }, { "_key" : "group:administrators:members", "value" : [ "1", "2", "3" ] }, { upsert: true })