title: Using StartAt from Firebase with Flutter Timestamps
body: <p>I'm saving some posts on Firestore with a timestamp property and then I query this posts ordered by timestamp. I'm trying to create a "loadMore" function then works when the user scrolls to bottom and loads more posts.</p>
  
  <p>I'm saving the posts this way:</p>
  
  <pre><code>Firestore.instance
    .collection('posts')
    .add(&lt;String, dynamic&gt; {
       'content': 'content,
       'likes': 0,
       'comments': 0,
       'timestamp': DateTime.now(),
     })
  </code></pre>
  
  <p>And trying to query this way:</p>
  
  <pre><code>Firestore.instance
    .collection('posts')
    .orderBy('timestamp', descending: true)
    .startAfter(
      []..add(posts.last.timestamp)
    )
    ..limit(5)
  </code></pre>
  
  <p>But, it keeps ignoring the "startAfter" and returning me a list starting with the first element of the collection and not with the next ones.</p>
  
  <p>Would love to get help using this type of query :)</p>