title: Flutter Query 3rd Level Collection in Cloud Firestore
body: <p>I have a DB that follows a main category, then subcategory, then a 3rd layer called tags.</p>
  
  <p>I can query the subcategories just fine... having a hard time with the 3rd layer.</p>
  
  <pre><code>Query collectionReference = Firestore.instance
                              .collection("mainCategories")
                              .document("cKKi9cGKZNbTzgFIkdob")
                              .collection("subCategories")
                              .document("DFUwcMvGce3cidbuJjhW")
                               .collection("tags");
  </code></pre>
  
  <p>DOing the following Queries the Subcategories just fine.</p>
  
  <pre><code>Query collectionReference = Firestore.instance
                                  .collection("mainCategories")
                                  .document("cKKi9cGKZNbTzgFIkdob")
                                  .collection("subCategories");
  </code></pre>