title: NSPredicate: filtering objects by day of NSDate property
body: <p>I have a Core Data model with an <code>NSDate</code> property. I want to filter the database by day. I assume the solution will involve an <code>NSPredicate</code>, but I'm not sure how to put it all together.</p>
  
  <p>I know how to compare the day of two <code>NSDate</code>s using <code>NSDateComponents</code> and <code>NSCalendar</code>, but how do I filter it with an <code>NSPredicate</code>?</p>
  
  <p>Perhaps I need to create a category on my <code>NSManagedObject</code> subclass that can return a bare date with just the year, month and day. Then I could compare that in an <code>NSPredicate</code>. Is this your recommendation, or is there something simpler?</p>