title: BadArgumentError: _MultiQuery with cursors requires __key__ order in ndb
body: <p>I can't understand what this error means and apparently, no one ever got the same error on the internet</p>
  
  <blockquote>
    <p>BadArgumentError: _MultiQuery with cursors requires <code>__key__</code> order</p>
  </blockquote>
  
  <p>This happens here:</p>
  
  <pre><code>return SocialNotification.query().order(-SocialNotification.date).filter(SocialNotification.source_key.IN(nodes_list)).fetch_page(10)
  </code></pre>
  
  <p>The property <code>source_key</code> is obviously a key and <code>nodes_list</code> is a list of entity keys previously retrieved.</p>
  
  <p>What I need is to find all the <code>SocialNotifications</code> that have a field <code>source_key</code> that match one of the keys in the list. </p>