title: How to query nested objects in firestore
body: <p>I want to store data in following format:</p>
  
  <pre><code>{
     "chatName": "Football",
     "chatMembers":
     [
        {
           "userId": "nSWnbKwL6GW9fqIQKREZENTdVyq2",
           "name": "Niklas"
        },
        {
           "userId": "V3QONGrVegQBnnINYHzXtnG1kXu1",
           "name": "Timo"
        },
     ]
  } 
  </code></pre>
  
  <p>My goal is to get all chats, where the signed in user with a <code>userId</code> is in the <code>chatMembers</code> list. If the <code>userId</code> of the signed in user is not in the <code>chatMembers</code> property, then that chat should be ignored. Is this possible? </p>
  
  <p>If this is not possible, how can i achive this with subcollections?</p>
  
  <p>My development language is dart, but you can also post solutions in other languages.</p>
  
  <p>My current attempt is this, but this is not working:</p>
  
  <pre><code>_firestore.collection(collectionName).where("chatMembers.userId", isEqualTo: userId).snapshots()
  </code></pre>