edit core data model objects in a loop - ios

Question

I am trying to edit existing objects in Core Data storage. When i edit each object's attribute without a loop this works fine, but when I try to do it in a for loop, only my last object gets new attributes.
Here is the code I use to edit objects without a loop. This code works fine):
NSFetchRequest *songsRefreshRequest = [[NSFetchRequest alloc] initWithEntityName:#"Music"];
songsRefreshRequest.predicate = nil;
songsRefreshRequest.sortDescriptors = #[[NSSortDescriptor sortDescriptorWithKey:#"name"
ascending:YES
selector:#selector(localizedStandardCompare:)]];
NSError *frError;
NSArray *fetchedSongs = [self.context executeFetchRequest:songsRefreshRequest error:&frError];
fetchedSongs ? : NSLog(#"Error in fetch while refreshing songs: %#", [frError localizedDescription]);
NSString *song1path = [[NSBundle mainBundle] pathForResource:#"Beautiful-birds-song-in-the-morning" ofType:#"mp3"];
NSString *song2path = [[NSBundle mainBundle] pathForResource:#"Birds-singing-relaxation" ofType:#"mp3"];
NSString *song3path = [[NSBundle mainBundle] pathForResource:#"Morning Melody" ofType:#"mp3"];
Music *song1 = (Music *) [fetchedSongs objectAtIndex:0];
Music *song2 = (Music *) [fetchedSongs objectAtIndex:1];
Music *song3 = (Music *) [fetchedSongs objectAtIndex:2];
song1.name = #"Beautiful-birds-song-in-the-morning";
song2.name = #"Birds-singing-relaxation";
song3.name = #"Morning Melody";
song1.path = song1path;
song2.path = song2path;
song3.path = song3path;
Here is the code I use to edit song's attributes in a loop (code below somehow edit a path for only the last object (song3 in my case), other object's path attribute becomes NULL. And I can't figure out why):
for (Music *iterSong in fetchedSongs){
NSString *iterSongName = [iterSong valueForKey:#"name"];
iterSong.path = [[NSBundle mainBundle] pathForResource: iterSongName ofType:#"mp3"];
}
I have already tried to change for each to for (int i=0; i<[fetchedSongs count]; i++) this didn't help. Cycle repeats as many times as many songs are in the model and only changes the last song's path. Appreciate any help, thanks in advance!
P.S. The whole loop code:
for (Music *iterSong in fetchedSongs){
//Music *iterSong = (Music*) [fetchedSongs objectAtIndex:i];
NSLog(#"inerSong.name = %#", iterSong.name);
NSLog(#"inerSong.oldPath = %#", iterSong.path);
NSString *iterSongName = [iterSong valueForKey:#"name"];
NSString *iterSongPath = [[NSBundle mainBundle] pathForResource: iterSongName ofType:#"mp3"];
NSLog(#"iterSongPath (string) = %#", iterSongPath);
iterSong.path = iterSongPath;
NSLog(#"iterSong.newPath = %#", iterSong.path);
}
if ([self.context hasChanges]){
NSError *error;
if (![self.context save:&error]){
NSLog(#"error while saving context after refreshing song paths: %#", [error localizedDescription]);
}
}

Answer 1

First, I assume you run that loop inside the NSManagedObjectContext performBlock method. Second, you need to save your changes to your NSManagedObjects context after you edit your objects.
Objective-C:
NSError *error = nil;
if ([[self managedObjectContext] save:&error] == NO) {
NSAssert(NO, #"Error saving context: %#\n%#", [error localizedDescription], [error userInfo]);
}
Swift:
do {
try managedObjectContext.save()
} catch {
fatalError("Failure to save context: \(error)")
}

Answer 2

Problem solved this way:
I removed all the hyphens from files' names. And the code started to work fine with the same loop. Also I converted files from mp3 to wav. But I suppose that problem existed because file can't include hyphen in its name.
Thanks everyone who answered!