angular - Trying to make a Angular2 service that updates Firebase and returns an Observable -

i want make method on service works angularfire2 , returns observable. want update counter (updating counter may not scalable example, not matter here). attempt service:

import { injectable } '@angular/core'; import { angularfire } 'angularfire2'; import { observable } 'rxjs/observable'; import 'rxjs/add/operator/map';  @injectable() export class myservice {    constructor(private af: angularfire) { }    updatecounter(): observable<any>  {     let counterobserver = this.af.database.object('/variousdata/counter');     counterobserver.take(1).subscribe(res => {       let counter = res.$value;       return this.af.database.object('/variousdata').update({counter: counter+1});     });     return counterobserver;   }  } 

and using this:

let resultobservable = this.myservice.updatecounter(); resultobservable.subscribe(   (obj) => {     console.log('result:', json.stringify(obj));   } } 

but getting first result (getting counter value) printed console. how can (or only) second one?

i have been inspired example found in observable type 2 http.get calls in angular 2, example did not work firebase case, have tried alter it...