Query a specific list of data from Firebase RTDB?

Question

Is there a better way to query a specific set of data in Firebase RTDB than this? All I can think of is using forEach() and pushing to a BehaviorSubject inside subscribe on each observable emitted. Let me know! I've been stuck on this for a while.

hits = new BehaviorSubject([]);

territories = ['16830', '16832', '16838'] // Zip Codes

getTerritories(territories) {
    territories.forEach(key => {
      this.db.object(`locations/${key}`).snapshotChanges()
      .map(zip => zip.payload.val())
      .subscribe(zip => {
        let currentHits = this.hits.getValue();
        currentHits.push(zip);
        this.hits.next(currentHits);
      });
    });
   }

this.hits.subscribe(res => console.log(res));

Answer 1

You can use Observable.forkJoin():

Observable.forkJoin(
    //this returns an array of observables.
    territories.map(key => this.db.object(`locations/${key}`)
        .map(zip => zip.payload.val()))
)
    .subscribe(res => console.log(res));

Note that Observable.forkJoin takes in an array of observables, and fires them in parallel, wait for all of them to complete, before emitting a value.