Saving an instance of an NSManagedObjectContext does not permanently save a mutable transformable attribute

I'm using Core Data + sqlite as a data cache. The app reads in a file into core data, then uses Core Data to run the app. Saves are done to both the NSManagedObjectContext and to the file. I've noticed, though, if I quit the app and reload it without repopulating the Core Data database, some (but not all) of the data saved using -save: is not being saved to the data store.

Changes to my managed object are all done in a single batch on the main thread, with the -save: message being sent after all changes are comple开发者_运维百科ted. The data that isn't being saved is a transformable attribute, the only transformable attribute in the core data object. Here's the code that saves the object:

    NSInteger columnIndex = [headers indexOfObject:questionID];
    if (NSNotFound != columnIndex) {

                    // parsedLine is a mutable array already
        NSMutableArray *parsedLine = person.dataFromFile.parsedLine;
        [parsedLine replaceObjectAtIndex:columnIndex withObject:answer];
        person.dataFromFile.parsedLine = parsedLine;

        person.questionsAnsweredByPerson = [NSNumber numberWithInt:[FileParser questionsAnsweredInRow:person.dataFromFile.parsedLine withRowHeaders:headers]];

        person.address.street.questionsAnsweredByPeopleOnStreet = [NSNumber numberWithInt:[self questionsAnsweredByPeopleOnStreet]];

        //NSLog(@"rawLineBefore:\n%@", person.dataFromFile.rawLine);
        person.dataFromFile.rawLine = [ReconstructCSV composeCSVLineFromArray:person.dataFromFile.parsedLine];
        //NSLog(@"rawLineAfter:\n%@", person.dataFromFile.rawLine);


        Voter_SurveyAppDelegate *appDelegate = (Voter_SurveyAppDelegate *)[[UIApplication sharedApplication] delegate];

        NSError *error;

        NSManagedObjectContext *managedObjectContext = [appDelegate managedObjectContext];
        if (![managedObjectContext save:&error]) {
            // XXX inform the user there was a fatal error opening the file. Low disk space?
            NSLog(@"Unresolved error - could not save managedObjectContext - %@, %@", error, [error userInfo]);
            abort();
        }
        return YES;
    }

abort(); is not getting called, so I assume -save; is getting called properly.

I doubt it is related, but after this code is run on the main thread, I perform an NSFetchRequest using a new NSManagedObjectContext on a different thread. Nothing else takes place related to Core Data on other threads.

Why isn't the transformable attribute getting saved?

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The problem is that transformable properties don't like Mutable objects. As noted in an answer to this question, an NSMutableDictionary wasn't getting saved. In my case, it was an NSMutableArray.