title: About NSPredicate in Core Data Fetch
body: <p>I have two entities, User &amp; Message.</p>
  
  <ul>
  <li>Message has a created_at timestamp;</li>
  <li>Message has a sender[to one relationship with User];</li>
  <li>User has a sentMessages[to many relationship with Message];</li>
  </ul>
  
  <p>However I want to fetch all users who have sent any messages and with their latest sent message fetched together.</p>
  
  <p>I've try fetch message and set predicate </p>
  
  <pre><code>created_at = sender.sentMessages.@max.created_at
  </code></pre>
  
  <p>but the compiler told me unable to parse sql statement?
  How can I do that?</p>