'Joining' Firebase Queries in Angularfire2

Question

Update:

The issues I was encountering with the empty value fields had to do with non-existent keys in my database, so most of the discourse here won\'t apply to yo

Answer 1

To solve joins on users, I wrote a service that caches the users already fetched and maps them into the referencing data with minimal code. It uses a nested map structure to do the join:

constructor(public db: AngularFireDatabase, public users:UserProvider) {
    this.threads = db.list('threads').valueChanges().map(messages => {
      return threads.map((t:Message) => {
        t.user = users.load(t.userid);
        return m;
      });
    });
}

And the UserProvider service looks like so:

@Injectable()
export class UserProvider {
  db: AngularFireDatabase;
  users: Map>;

  constructor(db: AngularFireDatabase) {
    this.db = db;
    this.users = new Map();
  }

  load(userid:string) : Observable {
    if( !this.users.has(userid) ) {
      this.users.set(userid, this.db.object(`members/${userid}`).valueChanges());
    }
    return this.users.get(userid);
  }
}

There's a complete working example of the joins and all the boilerplate here