func getObject<T : NSManagedObject>(id: Int, idString: String, context: NSManagedObjectContext = NSManagedObjectContext.MR_defaultContext()) -> T? {
      let predicate = NSPredicate(format: "%K = %@", idString, NSNumber(integer: id))
      guard let results = T.MR_findAllWithPredicate(predicate, inContext: context) as? [T] else {
          return nil
      }
      if results.count >= 1 {
          return results[0]
      }
      return nil
  }

  // Usage
  var user = getObject(123, idString: "userID", context: context) as User?