Creating and assigning a new NSManagedObject to a new NSManagedObject *sometimes* fails - swift

Question

I am creating a new NSManagedObject called "translation". Within the translation I need to create two additional NSManagedObjects called "phrase". Sometimes one of the phrase assignments will throw an error, but when I inspect the values they all look like they were created just fine. What gives???
Creating A Translation Object:
func getOrCreateTranslation(package: Package?, data: NSDictionary) -> Translation {
let translationId = data["id"] as! NSNumber
if let translation = self.getTranslation(translationId) {
return translation
} else {
let context = LocalDataStorage().context
let translation = NSEntityDescription.insertNewObjectForEntityForName("Translation", inManagedObjectContext: context) as! Translation
translation.id = translationId
let fromPhrase = data["from_phrase"]! as! NSDictionary
let toPhrase = data["to_phrase"]! as! NSDictionary
let pm = PhraseManager()
//*******
// *SOMETIMES* ONE OF THESE LINES FAIL WITH BAD_EXC_ACCESS code=1
translation.fromPhrase = pm.getOrCreatePhrase(fromPhrase)
translation.toPhrase = pm.getOrCreatePhrase(toPhrase)
//******
if package != nil {
package!.addTranslationObject(translation)
}
return translation
}
}
Creating A Phrase Object:
func getOrCreatePhrase(data: NSDictionary) -> Phrase {
// check if phrase exists
let phraseId = data["id"] as! NSNumber
if let phrase = self.getPhrase(phraseId) {
return phrase
} else {
let context = localDataStorage.context
let lm = LanguageManager()
let phrase = NSEntityDescription.insertNewObjectForEntityForName("Phrase", inManagedObjectContext: context) as! Phrase
phrase.id = phraseId
phrase.text = data["text"] as! String
phrase.audioUrl = data["audio_url"] as? String
let code = data["language"]!["language_code"] as! String
phrase.language = lm.getLanguageFromCode(code)
return phrase
}
}
Call Made to API:
func getPackageTranslations(package: Package, completion: ([Translation])-> Void) {
let currentLanguage: Language = LanguageManager().getCurrentLanguage()!
let urlString = baseAPIString + "/groups/\(package.id!)/translations/?language_code=\(currentLanguage.code)"
let session = NSURLSession.sharedSession()
let serachUrl = NSURL(string: urlString)
let task = session.dataTaskWithURL(serachUrl!) {
(data, response, error) -> Void in
if error != nil {
print(error?.localizedDescription)
} else {
let jsonData: NSDictionary!
do {
jsonData = try NSJSONSerialization.JSONObjectWithData(data!, options: .MutableContainers) as! NSDictionary
} catch _ {
jsonData = NSDictionary()
}
let groupTranslationsData = jsonData["group_translations"] as! [NSDictionary]
var translations = [Translation]()
let context = LocalDataStorage().context
for groupTranslation in groupTranslationsData {
let translationData = groupTranslation["translation"] as! NSDictionary
let translation = TranslationManager().getOrCreateTranslation(package, data: translationData)
if translation.packages?.containsObject(package) == false {
//package.addTranslationObject(translation!)
//translation!.addPackageObject(package)
}
translations.append(translation)
}
do {
try context.save()
} catch {
print("There was a problem saving translation ")
}
dispatch_async(dispatch_get_main_queue(), {
completion(translations)
})
}
}
task.resume()
}
CoreData Context Class:
class LocalDataStorage {
let appDelegate: AppDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
let context: NSManagedObjectContext!
init() {
context = appDelegate.managedObjectContext
}
}

Answer 1

This issue occurs when you create a NSManagedObjectContext with a concurrency pattern that it should be interacted on and you perform actions on the it on a thread different from the concurrency pattern specified during its initialization.
The completion block of NSURLSession.dataTaskWithURL is run on another thread, so you must dispatch to the type of thread specified in the context creation to perform any operation successfully on it.
If the concurrency type of your context is MainQueueConcurrencyType which is used in most cases, you must perform the context save method on the main queue.
dispatch_async(dispatch_get_main_queue()) {
do {
try context.save()
} catch {
print("There was a problem saving translation ")
}
completion(translations)
}