Kernel data error 133020: merge problems in save mode:

Question

First, I want to say that I do not use threads or multiple contexts, and I read and worked with every related answer I could find on SO. I have a project to which I added Core Data, and I find it impossible to find a fatal error. I can reproduce the error every time using the following code.

- (void)tableView:(UITableView *)tableView moveRowAtIndexPath:(NSIndexPath *)fromIndexPath toIndexPath:(NSIndexPath *)toIndexPath { OT_Track *track; track = [[self.tracksArray objectAtIndex: fromIndexPath.row] retain]; [self.tracksArray removeObjectAtIndex: fromIndexPath.row]; [self.tracksArray insertObject:track atIndex: toIndexPath.row]; [track release]; for( int n = 0; n < [self.tracksArray count]; n++ ) { track = [self.tracksArray objectAtIndex:n]; track.positionInPlaylist = [NSNumber numberWithInteger:n]; } if( [self.managedObjectContext hasChanges] && ![self.managedObjectContext save:&error] ) { NSLog(@"Unable to Save Core Data Context"); } } 

self.tracksArray is an NSMutableArray populated from a selection done in viewWillAppear. OT_Track is an entity defined in my mom that has a field called positionInPlaylist (defined as Integer32). positionInPlaylist saves the OT_Track position in OT_Playlist, which allows the user to reorder items in the playlist.

I would be so grateful for any help on this subject, since he turned me on!

I get an error.

 ************** Error ******** The operation couldn't be completed. (Cocoa error 133020.) 2012-03-27 13:03:32.578 OneTrack[7693:707] detailedErrors: (null) 2012-03-27 13:03:32.587 OneTrack[7693:707] { conflictList = ( "NSMergeConflict (0x4018590) for NSManagedObject (0x40d7e60) with objectID '0x40debd0 <x-coredata://3A300D46-4B20-46DA-A82E-0785BFFAFF14/OT_Track/p2642>' with oldVersion = 1 and newVersion = 2 and old cached row = {\n artistName = \"Ladysmith Black Mambazo\";\n disabled = 0;\n persistentID = \"-2511068126837362989\";\n playing = 0;\n playlist = \"0x401a7a0 <x-coredata://3A300D46-4B20-46DA-A82E-0785BFFAFF14/OT_Playlist/p62>\";\n podcast = 0;\n positionInPlaylist = 0;\n trackAutoplay = 0;\n trackEndTime = \"222.563\";\n trackLoop = 0;\n trackMaxTime = \"222.563\";\n trackName = Abezizwe;\n trackPredelay = 0;\n trackSignature = 2;\n trackStartTime = 0;\n trackTempo = 120;\n trackVolume = 1;\n} and new database row = {\n artistName = \"Ladysmith Black Mambazo\";\n disabled = 0;\n persistentID = \"-2511068126837362989\";\n playing = 0;\n playlist = \"0x40188b0 <x-coredata://3A300D46-4B20-46DA-A82E-0785BFFAFF14/OT_Playlist/p62>\";\n podcast = 0;\n positionInPlaylist = 2;\n trackAutoplay = 0;\n trackEndTime = \"222.563\";\n trackLoop = 0;\n trackMaxTime = \"222.563\";\n trackName = Abezizwe;\n trackPredelay = 0;\n trackSignature = 2;\n trackStartTime = 0;\n trackTempo = 120;\n trackVolume = 1;\n}", "NSMergeConflict (0x4018610) for NSManagedObject (0x40dc990) with objectID '0x40deed0 <x-coredata://3A300D46-4B20-46DA-A82E-0785BFFAFF14/OT_Track/p2645>' with oldVersion = 1 and newVersion = 2 and old cached row = {\n artistName = \"Warren Zevon\";\n disabled = 0;\n persistentID = \"-2511068126837362101\";\n playing = 0;\n playlist = \"0x401ac40 <x-coredata://3A300D46-4B20-46DA-A82E-0785BFFAFF14/OT_Playlist/p62>\";\n podcast = 0;\n positionInPlaylist = 3;\n trackAutoplay = 0;\n trackEndTime = \"223.686\";\n trackLoop = 0;\n trackMaxTime = \"223.686\";\n trackName = \"Accidentally Like A Martyr\";\n trackPredelay = 0;\n trackSignature = 2;\n trackStartTime = 0;\n trackTempo = 120;\n trackVolume = 1;\n} and new database row = {\n artistName = \"Warren Zevon\";\n disabled = 0;\n persistentID = \"-2511068126837362101\";\n playing = 0;\n playlist = \"0x4018420 <x-coredata://3A300D46-4B20-46DA-A82E-0785BFFAFF14/OT_Playlist/p62>\";\n podcast = 0;\n positionInPlaylist = 3;\n trackAutoplay = 0;\n trackEndTime = \"223.686\";\n trackLoop = 0;\n trackMaxTime = \"223.686\";\n trackName = \"Accidentally Like A Martyr\";\n trackPredelay = 0;\n trackSignature = 2;\n trackStartTime = 0;\n trackTempo = 120;\n trackVolume = 1;\n}" ); } 

self.tracksArray is populated with the following method called from viewWillAppear ...

 - (BOOL) populateTracksArray { NSFetchRequest *request = [[NSFetchRequest alloc] init]; NSEntityDescription *entity = [NSEntityDescription entityForName:@"OT_Track" inManagedObjectContext:self.managedObjectContext]; [request setEntity:entity]; NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"positionInPlaylist" ascending:YES]; NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil]; [request setSortDescriptors:sortDescriptors]; NSPredicate *fetchPredicate = [NSPredicate predicateWithFormat:@"playlist == %@", currentUserPlaylist]; [request setPredicate:fetchPredicate]; [sortDescriptors release]; [sortDescriptor release]; NSError *error = nil; NSMutableArray *mutableFetchResults = [[managedObjectContext executeFetchRequest:request error:&error] mutableCopy]; if (mutableFetchResults == nil) { // Handle the error. return false; } [self setTracksArray:mutableFetchResults]; [mutableFetchResults release]; [request release]; return true; } 

Answer 1

I'm still not quite sure what caused this, but the problem recurred, and I solved it, making sure that any methods that referred to the main data were executed in the main thread using performSelectorOnMainThread.

Answer 2

Have you tried to establish a merge policy in the context of a managed entity?

The default is NSErrorMergePolicy , which simply throws errors. Your other options are here .

I would suggest the following:

 [self.managedObjectContext setMergePolicy:NSMergeByPropertyObjectTrumpMergePolicy]; 

---

Just noticed something that might cause problems with your swap code.

Instead

 OT_Track *track; track = [[self.tracksArray objectAtIndex: fromIndexPath.row] retain]; [self.tracksArray removeObjectAtIndex: fromIndexPath.row]; [self.tracksArray insertObject:track atIndex: toIndexPath.row]; [track release]; 

try the code snippet from this blog post .

I think your track swapping code might cause indexes to get confused halfway through the swap.