title: Angular fetch data specific to every item of ngFor
body: <p>I have an array of items which themselfes have a "foreign key" that can uniquely identify other items that are based on a server.</p>
  
  <pre><code>&lt;div *ngFor="let parentItem of parentItems"&gt;
    {{(getChild(parentItem.childId) | async)?.someData}}
  &lt;/div&gt;
  
  getChild(id):Observable&lt;IChild&gt;{
    return this.childService.getChild(id);
  }
  </code></pre>
  
  <p>I would like to nest these items and display them.
  Sadly nothing shows in the child brackets even tough the values are shown correctly inside a regular subscriber when logging to the console.
  Also there seems to be another problem. The program tries to refetch it all the time. I think this has something to do with the change-detection, but i cannot figure out how to fix this.</p>