title: Leaderboard ranking with Firebase
body: <p>I have project that I need to display a leaderboard of the top 20, and if the user not in the leaderboard they will appear in the 21st place with their current ranking.</p>
  
  <p>Is there efficient way to this?</p>
  
  <p>I am using Cloud Firestore as a database. I believe it was mistake to choose it instead of MongoDB but I am in the middle of the project so I must do it with Cloud Firestore.</p>
  
  <p>The app will be use by 30K users. Is there any way to do it without getting all the 30k users?</p>
  
  <pre><code> this.authProvider.afs.collection('profiles', ref =&gt; ref.where('status', '==', 1)
          .where('point', '&gt;', 0)
          .orderBy('point', 'desc').limit(20))
  </code></pre>
  
  <p>This is code I did to get the top 20 but what will be the best practice for getting current logged in user rank if they are not in the top 20?</p>