title: Firebase update the retrieved document
body: <p>I have a collection in my Firebase with documents, where I retrieve data in the following way:</p>
  <pre><code> self.db.collection(&quot;ustas&quot;).order(by: &quot;stats&quot;).limit(to: 20).getDocuments() { (querysnapshot,err) in
           for document in querysnapshot!.documents {
           }
  }
  </code></pre>
  <p>I want to perform some actions, but after that, I want to update the <code>impressions+=1</code>, for each document. Is it possible to dynamically do it?</p>