title: Listen to multiple sub-collections - Firebase Flutter
body: <p>I have database structure as:</p>
  <pre><code>=&gt; collection (ChatRoom) : stores chat room name, chat participants, unique chat room id
   =&gt; documents (unique ids) : documents created with unique ids based upon users
    =&gt; sub-collection (chats) : all chats going on between 2 specified persons (chat participants)
  </code></pre>
  <p>Now, i want to listen to multiple chats collection based upon user.
  For example :</p>
  <p>If a user is connected with 500 people then how can i listen to those <strong>500 chats(sub-collections)</strong> in order to get notified when a new message is being sent by any one of them.</p>
  <p>Also, isn't that cause much of a <strong>performance overhead</strong> for the device.</p>
  <p>Also, taking in account the <strong>db reads</strong> for such scenario, are they going to be too much.</p>
  <p>What should be the best method for such situation ?</p>