title: Query a specific list of data from Firebase RTDB?
body: <p>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.</p>
  
  <pre><code>hits = new BehaviorSubject([]);
  
  territories = ['16830', '16832', '16838'] // Zip Codes
  
  getTerritories(territories) {
      territories.forEach(key =&gt; {
        this.db.object(`locations/${key}`).snapshotChanges()
        .map(zip =&gt; zip.payload.val())
        .subscribe(zip =&gt; {
          let currentHits = this.hits.getValue();
          currentHits.push(zip);
          this.hits.next(currentHits);
        });
      });
     }
  
  this.hits.subscribe(res =&gt; console.log(res));
  </code></pre>