title: Swift fetchRequest with multiple sortDescriptors and Bool filter
body: <p>I am fetching from core data. I have an attribute that is a bool that is saved with a time attribute. I need to return an array of dates where the bool is true. I cannot get it to work, I either get an array of empty dates or it crashes.</p>
  
  <pre><code>func datesWithCompleteHBI() -&gt; [Date] {
  
    let managedObjectContext = (UIApplication.shared.delegate as! AppDelegate).managedObjectContext
    fetchRequest.resultType = .dictionaryResultType
    fetchRequest.propertiesToFetch = ["savedTime", "harveyBradshawIndexComplete"]
  
    let timeSort = NSSortDescriptor(key: "savedTime", ascending: false)
    let hbiSort = NSSortDescriptor(key: "harveyBradshawIndexComplete", ascending: false)
    fetchRequest.sortDescriptors = [timeSort, hbiSort]
  
    let messageKey = true
    fetchRequest.predicate = NSPredicate(format: "harveyBradshawIndexSaveLevel = %@", messageKey as CVarArg)
  
    var dates = [Date]()
    do {
  
        let results = try managedObjectContext.fetch(fetchRequest) as! [[String:Date]]
  
        dates = results.flatMap { $0["savedTime"]}
  
       } catch let error as NSError {
         print("Could not fetch \(error), \(error.userInfo)")
  
      }
  
   print("hbi date array \(dates)")
   return dates
   }
  }
  </code></pre>