title: NSPredicate for searching within relationship entities
body: <p>I have an entity called Band which has a to-many relationship to a Category entity. The Category entity just contains a categoryName string attribute.</p>
  
  <p>An example record:</p>
  
  <pre><code>Band:       
    bandName: Kiss
    bandCategories:   -  &gt; BandCategory:categoryName:Glam
                      -  &gt; BandCategory:categoryName:Rock
  </code></pre>
  
  <p>How would I use NSPredicate to search thru all my Bands for bands which match the Rock category, for example?</p>