title: Firebase Firestore order by not working
body: <p>I am learning about Firebase Firestore through official documentation. I was trying following code. Notifications are added using add() method of firestore.</p>
  
  <pre><code>FirebaseFirestore.getInstance().colRefNotifications()
              .orderBy("timestamp", Query.Direction.DESCENDING)
              .get()
              .addOnSuccessListener(new OnSuccessListener&lt;QuerySnapshot&gt;() {
          @Override
          public void onSuccess(QuerySnapshot documentSnapshots) {
  
              if (!documentSnapshots.isEmpty()){
  
                  listNotifications.clear();
                  recyclerViewNotification.removeAllViews();
  
                  for (DocumentSnapshot data : documentSnapshots){
  
                      Notification notification = data.toObject(Notification.class);
                      listNotifications.add(notification);
                  }
  
                  notificationGeneralAdapter.notifyDataSetChanged();
              }
          }
      });
  </code></pre>
  
  <p><strong>Notification.java</strong></p>
  
  <pre><code>private String text;
  private String key;
  private Date timestamp;
  
  public Notification() {
  }
  
  public Notification(String text, String key, Date timestamp) {
      this.text = text;
      this.key = key;
      this.timestamp = timestamp;
  }
  
  public String getText() {
      return text;
  }
  
  public String getKey() {
      return key;
  }
  
  public Date getTimestamp() {
      return timestamp;
  }
  </code></pre>
  
  <p><strong>Firestore</strong></p>
  
  <p><a href="https://i.stack.imgur.com/9Q4WI.png" rel="noreferrer"><img src="https://i.stack.imgur.com/9Q4WI.png" alt="firestore_snapshot"></a></p>
  
  <p>I am ordering notifications by timestamp in descending direction. But, as you can see in the following snapshot, it is not showing desired output.</p>
  
  <p><a href="https://i.stack.imgur.com/ASqIy.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/ASqIy.jpg" alt="Snapshot"></a></p>
  
  <p>What am I doing wrong? Thank you for your help.</p>