title: Update a document in firestore
body: <p>I would like the update a document in Firebase. The problem is that you can only update a specific field?</p>
  
  <p>I would like to do something like this:</p>
  
  <pre><code>fs.collection("users").document(user.id).update(user)
  </code></pre>
  
  <p>The problem is that Kotlin forces to put a field in update, like this:</p>
  
  <pre><code>fs.collection("users").document(user.id).update("firstname", user)
  </code></pre>
  
  <p>But I don't want that, I want to update the whole document with my model not a field.</p>