title: Getting the user id from a Firestore Trigger in Cloud Functions for Firebase?
body: <p>In the example bellow, is there a way to get the user id (uid) of the user who wrote to 'offers/{offerId}'? I tried to do as described <a href="https://stackoverflow.com/questions/42750060/getting-the-user-id-from-a-database-trigger-in-cloud-functions-for-firebase">here</a> but it doesn't work in Firestore.</p>
  
  <pre><code>exports.onNewOffer = functions.firestore
    .document('offers/{offerId}')
    .onCreate(event =&gt; {
      ...
  });
  </code></pre>