title: Firestore - subcollection query for a specific document
body: <p><strong><em>Note: Querying across subcollections is not currently supported in Cloud Firestore. If you need to query data across collections, use root-level collections.</em></strong></p>
  
  <p>When I read the documentation for me it's not clear if it's possible to do something like this:</p>
  
  <pre><code>var listsRef = db.collection("users/user1/lists");
  var query = listsRef.where("public", "==", true);
  </code></pre>
  
  <p>I can understand that it's not supported if I try to do this:</p>
  
  <pre><code>var listsRef = db.collection("users/{userId}/lists");
  var query = listsRef.where("public", "==", true);
  </code></pre>
  
  <p>But I am wondering if I can query in a specific collection that comes from a specific document. In fact, what's the difference here and in a root collection?</p>
  
  <p>Thanks in advance.</p>