How to join multiple documents in a Cloud Firestore query?

Ionic Framework ionic-v3
1

I have a Firestore DB with the following structure:

  • users

    • [uid]
      • name: “User teste”

  • artists

    • [id]
      • content: “Some teste.”
      • timestamp: (Dec. 22, 2017)
      • uid: [uid]

And in my service

  constructor(private afu: AngularFireAuth, private afs: AngularFirestore, private storage: AngularFireStorage) { 
    this.usersCollection = afs.collection<User>('users');
    this.users = this.usersCollection.valueChanges();
  }

my method to get users

  getUsers() {
    return this.users = this.usersCollection.snapshotChanges()
      .pipe(map(changes => {
        return changes.map(action => {
          const data = action.payload.doc.data() as User;
          return data
        });
      }));
  }

How to use join between documents ?

user name: User teste
user content: Some teste.

2

see this also