title: Flutter Firestore StreamBuilder on list of references
body: <p>The Firestore database is build of one collection of users. Every user document has some public data and a array of users ID's that he follows called following. In the Flutter app I would like to create a StreamBuilder on the following array. So when the user adds someone to his following array - it would be added to the stream, and when a user from the following list changes his data - the stream would update too.</p>
  
  <p>I thought maybe to use a list of references (<code>'users/usersid3'</code>) instead of a list of IDs (<code>'userid3'</code>), but I don't know how to implement it.</p>
  
  <p>This is how the database is structured.</p>
  
  <pre><code>users
        - user1id
              - some public data
              - following: [user2id, user3id]
        - user2id
              - some public data
              - following: []
        - user3id
              - some public data
              - following: [user2id]
  </code></pre>