title: Chain multiple calls with foreach loop and Observable
body: <p>I want to chain multiple request to the urls which I get from the array. Before next chain i want to wait for the previous one to finish. It's does not matter if the previous fails or not. I was trying to this with forkJoin but I know that if one of the request fails it will return error.</p>
  
  <pre><code>this.dataServers.forEach(dataServer =&gt; {
      observableBatch.push(this.getFoodsByQuery(dataServer.url, query));
  });
  
  return Observable.forkJoin(observableBatch).subscribe(data =&gt; {
      this.searchingServer.next(null);
      observer.complete();
  });
  </code></pre>
  
  <p>I do not know how to do this with flatMap.</p>