title: How to get the number of Firestore documents in flutter
body: <p>I am building a flutter app and using Cloud Firestore. I want to get the number of all documents in the database.</p>
  
  <p>I tried</p>
  
  <pre><code>Firestore.instance.collection('products').toString().length
  </code></pre>
  
  <p>but it didn't work.</p>