How to get a list of fields in a MongoDB document?

Question

MongoDB

There is a Mongo base, there is a certain document with collections. Is there any possibility, preferably through mongoengine, to get the list of field names?
For example
class User(db.Document):
login = db.StringField()
name = db.StringField()
aboutme = db.StringField()
at the output get the list ['login', 'name', 'aboutme']

Answer 1

mr = db.runCommand({
  "mapreduce" : "my_collection",
  "map" : function() {
    for (var key in this) { emit(key, null); }
  },
  "reduce" : function(key, stuff) { return null; }, 
  "out": "my_collection" + "_keys"
})

db[mr.result].distinct("_id")

Answer 2

No. MongoDB is a schemaless database, completely different documents can be stored in the same collection (another thing is that in practice this is not necessary).
You can iterate the entire (or not all) collection and see which fields of which type are encountered.