title: NSPredicate based on content of relationship
body: <p>I have an entity <code>MyEntity</code> that has a <code>tags</code> to-many relationship, so <code>tags</code> is an <code>NSSet</code> of <code>MyEntity</code>. It's optional, so some <code>MyEntity's</code> don't have <code>tags</code>. Here's what I'm trying to do:</p>
  
  <pre><code> predicate= [NSPredicate predicateWithFormat:
   @"(rootId == parentId AND NONE tags.tagName == %@)", @"badTag"];
  </code></pre>
  
  <p>So I want to get all <code>MyEntitys</code> where <code>rootId == parentId</code> and don't give me any entities if its tags has a tag named <code>"badTag"</code>. The problem with this is that if the entity does not have any tags at all, that entity is not returned. I've tried a variation of the above:</p>
  
  <pre><code> @"(rootId == parentId AND ANY tags.tagName != %@)", @"badTag"];
  </code></pre>
  
  <p>But this gives the same result. How can I make this predicate work for the case where the entity does not have any tags at all?</p>