title: Declare a read-only @NSManaged property in Swift for Parse's PFRelation
body: <p>I'm using <a href="https://parse.com/docs/ios/guide#objects-properties-amp-methods">Parse object store</a> in my iOS application and I've created a custom subclass for my Parse object, which looks somewhat like this:</p>
  
  <pre><code>class MyThing: PFObject, PFSubclassing {
  
     // ...PFSubclassing protocol...
  
     @NSManaged var name: String
     @NSManaged var somethingElse: String
     @NSManaged var relatedThings: PFRelation
  
   }
  </code></pre>
  
  <p>The <code>relatedThings</code> property works: I am able to fetch the related objects from the store. However, I keep getting this warning from Parse:</p>
  
  <pre><code>[Warning]: PFRelation properties are always readonly,
  but MyApp.MyThing.relatedThings was declared otherwise.
  </code></pre>
  
  <p>In Objective-C, I could have easily marked that property as readonly, but I am unsure how to do that in Swift to silence the warning.</p>
  
  <p>Using <code>let</code> instead of <code>var</code> is not allowed in combination with <code>@NSManaged</code>.</p>
  
  <p>Adding <code>private(set)</code> has no effect either:</p>
  
  <pre><code>@NSManaged private(set) var relatedThings: PFRelation
  </code></pre>
  
  <p>So how does Parse expect me to declare the relationship property?</p>