title: How to sort randomly with CoreData
body: <p>I am using NSFetchRequest to fetch some items, which could be sorted by Popular, or Random. </p>
  
  <p>Following the guides, I could sort the items by popularity easily using NSSortDescriptor. </p>
  
  <pre><code>    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"popularity" ascending:NO];
      NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
      [request setSortDescriptors:sortDescriptors];
  </code></pre>
  
  <p>But how do I sort them randomly?</p>