Firebase - Firestore - get key with collection.add()

Question

I am facing a problem with the new Firestore from Firebase.

Situation: I have a collection(\'room\')

I create room with c

Answer 1

ANGULARFIRE:

get ID before add database:

var idBefore =  afs.createId();
    console.log(idBefore );

ANDROID FIRESTORE:

String idBefore = db.collection("YourCol").document().getId();