title: How to get child keys from Firebase Database (Angular2)
body: <p>My Code (pictures below):</p>
  
  <pre><code>this.allStatisticsRef = afDatabase.list(`data/users/${this.currentUserID}/statistics`);
    this.allStatisticData = this.allStatisticsRef.snapshotChanges().map(changes =&gt; {
      return changes.map(c =&gt; ({ key: c.payload.key, ...c.payload.val() }));
  });
  </code></pre>
  
  <p>So my <code>key</code>value is "2016" and "2017". How I get the child keys "8" and "9"? Anyone an idea?</p>
  
  <p><strong>What I exactly expect:</strong></p>
  
  <p>To use the data like this in my view: <code>{{ data.key.childkey.value }}</code>
  I´m building a list separated by year and months. The example above would be: <code>{{ data.year.month.values }}</code> or as result <code>{{ data['2017']['8']['hours'] }}</code></p>
  
  <p>I want to write the view like this:</p>
  
  <pre><code>&lt;ion-list *ngFor="let data of allStatisticData | async"&gt;
  &lt;ion-list-header&gt;{{ data.key }} (Year)&lt;/ion-list-header&gt;
  &lt;ion-item&gt;
    &lt;ion-item-divider&gt;{{ data.childKey }} (Month)&lt;/ion-item-divider&gt;
    {{ value }} (Data)
  &lt;/ion-item&gt;
  </code></pre>
  
  <p></p>
  
  <p><img src="https://i.stack.imgur.com/uoWoN.png" alt="Firebase Data structure"> <br>
  <img src="https://i.stack.imgur.com/cqgWb.png" alt="Result - Object"></p>