title: Creating NSSortDescriptor
body: <p>I'm trying to do a fetch on an entity for "Contractor". Contractor has a one-to-many relationship with another entity called "Job". So a contractor can have many jobs.</p>
  
  <p>How would I create a NSSortDescriptor so my fetch is sorted by number of jobs the contractor has -- from greatest to least?</p>
  
  <p>Thank you</p>