title: Fetch multiple entities with relation between them with one NSFetchedResultController
body: <p>I have base class <code>Worker</code> and subclasses <code>Employee</code>, <code>Bookkeeper</code> and <code>Director</code> and entities for them in <code>xcdatamodeld</code>. 
  Now I want to use <code>NSFetchedResultController</code> to fetch them into <code>tableView</code> so that each entity in each section.
  I dont know how to do that with single frc.
  Any help.</p>
  
  <p><a href="https://i.stack.imgur.com/tDaDk.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/tDaDk.png" alt="enter image description here"></a></p>