title: Swift 3 NSPredicate relationship request returns empty array
body: <p>I have a big problem right now. I just updated my app to Swift 3 and with the Help of Stackoverflow I got everything running smooth so far, except for the predicates where i try to access a relationship.</p>
  
  <p>This is my old request which worked just fine with Swift 2.3</p>
  
  <pre><code>if let myStation = station {
          context.performAndWait {
              let request = ProcessDetail.fetchRequest() as! NSFetchRequest&lt;ProcessDetail&gt;
              // DOESNT WORK ANYMORE !!!!! NEW SWIFT
              request.predicate = NSPredicate(format: "process.station_ID = %@", myStation.station_ID! )
  
              do {
                  let processDetails = try context.fetch(request)
                  for processDetail in processDetails {
                      ansProcessDetails += 1
                      if processDetail.processdetail_checked == "yes" {
                          ansMasteredProcessDetails += 1
                      } else {
                          ansNotMasteredProcessDetails += 1
                      }
                  }
              } catch let error {
                  print(error)
              }
          }
  </code></pre>
  
  <p>But now with the Array of processDetails is empty. Any suggestions?</p>
  
  <p>Here is the important line of code again:</p>
  
  <pre><code>request.predicate = NSPredicate(format: "process.station_ID = %@", myStation.station_ID! )
  </code></pre>
  
  <p>Thanks Ben</p>