title: Adding Server Timestamp field to the Object which being added
body: <p>I have a <code>Challenge</code> object, which has it's own properties and I'm able to add it to the database successfully like this:</p>
  
  <pre><code>DocumentReference challengeRef=usersRef.document(loggedUserEmail).collection("challenges_feed").
                  document(callengeID);
  challengeRef.set(currentChallenge);
  </code></pre>
  
  <p>This is how it looks like in the database:</p>
  
  <p><a href="https://i.stack.imgur.com/AzfqG.png" rel="noreferrer"><img src="https://i.stack.imgur.com/AzfqG.png" alt="enter image description here"></a></p>
  
  <p>I'd like to make a new field in the database (under this challenge) which called <code>latestUpdateTimetamp</code>. This is how it <em>should</em> look like (I have added it manually):</p>
  
  <p><a href="https://i.stack.imgur.com/6ofim.png" rel="noreferrer"><img src="https://i.stack.imgur.com/6ofim.png" alt="enter image description here"></a></p>
  
  <p>I have tried to set it in the <code>constructor</code> of the <code>object</code> like this:</p>
  
  <pre><code>private Map&lt;String,String&gt; latestUpdateTimestamp;
  
  public Challenge(String id, String senderName,  String senderEmail) {   
              this.senderName=senderName;
              this.senderEmail = senderEmail;
  
              this.latestUpdateTimestamp= ServerValue.TIMESTAMP;
          }
  </code></pre>
  
  <p>But this is what I get in the <code>database</code>:</p>
  
  <p><a href="https://i.stack.imgur.com/xLCeH.png" rel="noreferrer"><img src="https://i.stack.imgur.com/xLCeH.png" alt="enter image description here"></a></p>
  
  <p><strong>I'm trying to add the <code>latestUpdateTimestamp</code> to the <code>Challenge</code> and the <code>Challenge</code> object itself to the database at the same call. Is it possible?</strong> </p>
  
  <p>Can I somehow add this <code>timestamp</code> as a property to this <code>object</code> before adding it? </p>
  
  <p>I know I'm able to make a new call and add this field, but I'm wondering if it's possible at once.</p>