Is this the correct use of NSFetchedResultsController? - objective-c

Question

Is this is correct us of NSFetchedResultsController's getter method with the most modern Object-C and LLVM compiler that doesn't require synthesizing properties?
- (NSFetchedResultsController *)fetchedResultsController {
if (_fetchedResultsController) {
return _fetchedResultsController;
}
if (!self.managedObjectContext) {
self.managedObjectContext = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
}
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Session" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];
[fetchRequest setPredicate: self.predicate];
[fetchRequest setFetchBatchSize:20];
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:#"timeStamp" ascending:NO];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
[fetchRequest setSortDescriptors:sortDescriptors];
NSFetchedResultsController *aFetchedResultsController= [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:nil];
aFetchedResultsController.delegate = self;
NSError *error = nil;
if (![aFetchedResultsController performFetch:&error]) {
NSLog(#"Unresolved error %#, %#", error, [error userInfo]);
abort();
}
return aFetchedResultsController;
}
In other parts of my code, I have this instead:
- (NSFetchedResultsController *)fetchedResultsController {
if (_fetchedResultsController) {
return _fetchedResultsController;
}
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Set" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];
[fetchRequest setPredicate:[NSPredicate predicateWithFormat: #"sets == %#", self.exercise]];
[fetchRequest setFetchBatchSize:20];
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:#"timeStamp" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
[fetchRequest setSortDescriptors:sortDescriptors];
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc]initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:nil];
aFetchedResultsController.delegate = self;
self.fetchedResultsController = aFetchedResultsController;
NSError *error = nil;
if (![self.fetchedResultsController performFetch:&error]) {
NSLog(#"Unresolved error %#, %#", error, [error userInfo]);
abort();
}
return self.fetchedResultsController;
}

Answer 1

In your first example, you never assign anything to the property or ivar, so the lazy loading will occur every time the property is accessed. This isn't right.
In your second example you assign to the property, (thereby triggering any side effects of the property setter) and also return the value of the property (which wouldn't take many errors to leave you with an infinite loop). It may work now but it would be easy to break with a careless update.
It would be cleaner to assign to the internal ivar and return that.
So, at the end of your first example:
_fetchedResultsController = aFetchedResultsController;
return _fetchedResultsController;