title: Core Data: fetch request for fetching entities in a one-many-one relationship
body: <p>Say I have 3 entities <code>Grandparent</code>, <code>Parent</code>, and <code>Child</code>. </p>
  
  <p><code>Grandparent - Parent</code> is a one to many relationship</p>
  
  <p><code>Parent - Child</code> is a many to one relationship</p>
  
  <p><code>Child</code> has an <code>age</code> attribute</p>
  
  <p>My goal is to get all <code>Child</code> entities of <code>Parent</code> where <code>Parent.grandparent</code> is a certain <code>Grandparent</code>. In addition, I'd like to sort the fetched results by <code>age</code>. I know I can do this in multiple steps, but my question is: how can I accomplish this in a single fetch request?</p>
  
  <p><strong>Edit</strong>: Perhaps this diagram will be a bit clearer than the description above.
  <img src="https://i.stack.imgur.com/OEbUq.png" alt="enter image description here"></p>