I am using the below code for a core data singleton. Below is my code. (based from NachoMan's [blog](http://nachbaur.com/blog/smarter-core-data). However the code is from his gist.

```
// DataManager.h
#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>

extern NSString * const DataManagerDidSaveNotification;
extern NSString * const DataManagerDidSaveFailedNotification;

@interface DataManager : NSObject {
}

@property (nonatomic, readonly, retain) NSManagedObjectModel *objectModel;
@property (nonatomic, readonly, retain) NSManagedObjectContext *mainObjectContext;
@property (nonatomic, readonly, retain) NSPersistentStoreCoordinator *persistentStoreCoordinator;
@property (nonatomic, readonly, retain) NSManagedObjectContext *managedObjectContext;

+ (DataManager*)sharedInstance;
- (BOOL)save;
- (BOOL)clearEntity:(NSString *)entityDescription;
- (NSManagedObjectContext*)managedObjectContext;

@end

// DataManager.m
#import "DataManager.h"

NSString * const DataManagerDidSaveNotification = @"DataManagerDidSaveNotification";
NSString * const DataManagerDidSaveFailedNotification = @"DataManagerDidSaveFailedNotification";

@interface DataManager ()

- (NSString*)sharedDocumentsPath;

@end

@implementation DataManager

@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;
@synthesize mainObjectContext = _mainObjectContext;
@synthesize objectModel = _objectModel;
@synthesize managedObjectContext = _managedObjectContext;

NSString * const kDataManagerBundleName = nil;//@"AP";
NSString * const kDataManagerModelName = @"APData";
NSString * const kDataManagerSQLiteName = @"APData.sqlite";

+ (DataManager*)sharedInstance {
    static dispatch_once_t pred;
    static DataManager *sharedInstance = nil;

    dispatch_once(&pred, ^{ sharedInstance = [[self alloc] init]; });
    return sharedInstance;
}

- (void)dealloc {
    [self save];
}

- (NSManagedObjectModel*)objectModel {
    if (_objectModel)
        return _objectModel;

    NSBundle *bundle = [NSBundle mainBundle];
    if (kDataManagerBundleName) {
        NSString *bundlePath = [[NSBundle mainBundle] pathForResource:kDataManagerBundleName ofType:@"bundle"];
        bundle = [NSBundle bundleWithPath:bundlePath];
    }
    NSString *modelPath = [bundle pathForResource:kDataManagerModelName ofType:@"momd"];
    NSLog(@"Path: %@",modelPath);
    _objectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:[NSURL fileURLWithPath:modelPath]];

    return _objectModel;
}

- (NSPersistentStoreCoordinator*)persistentStoreCoordinator {
    if (_persistentStoreCoordinator) {
        NSLog(@"PersistentStore Exists %@",_persistentStoreCoordinator);
        return _persistentStoreCoordinator;
    }
    NSLog(@"Persistent Stored DOESN'T EXIST");

    // Get the paths to the SQLite file
    NSString *storePath = [[self sharedDocumentsPath] stringByAppendingPathComponent:kDataManagerSQLiteName];
    NSURL *storeURL = [NSURL fileURLWithPath:storePath];

    // Define the Core Data version migration options
    NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                 [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption,
                 [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption,
                 nil];

    // Attempt to load the persistent store
    NSError *error = nil;
    _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:self.objectModel];
    if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType
                               configuration:nil
                                 URL:storeURL
                                 options:options
                                   error:&error]) {
        NSLog(@"Fatal error while creating persistent store: %@", error);
        abort();
    }
    NSLog(@"store: %@",_persistentStoreCoordinator);
    return _persistentStoreCoordinator;
}

- (NSManagedObjectContext*)mainObjectContext {
    if (_mainObjectContext)
        return _mainObjectContext;

    // Create the main context only on the main thread
    if (![NSThread isMainThread]) {
        [self performSelectorOnMainThread:@selector(mainObjectContext)
                       withObject:nil
                    waitUntilDone:YES];
        return _mainObjectContext;
    }

    _mainObjectContext = [[NSManagedObjectContext alloc] init];
    [_mainObjectContext setPersistentStoreCoordinator:self.persistentStoreCoordinator];

    return _mainObjectContext;
}

- (BOOL)save {
    if (![self.mainObjectContext hasChanges])
        return YES;

    NSError *error = nil;
    if (![self.mainObjectContext save:&error]) {
        NSLog(@"Error while saving: %@\n%@", [error localizedDescription], [error userInfo]);
        [[NSNotificationCenter defaultCenter] postNotificationName:DataManagerDidSaveFailedNotification
                                    object:error];
        return NO;
    }

    [[NSNotificationCenter defaultCenter] postNotificationName:DataManagerDidSaveNotification object:nil];
    return YES;
}

- (BOOL)clearEntity:(NSString *)entityDescription
{
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:entityDescription inManagedObjectContext:_managedObjectContext];
    [fetchRequest setEntity:entity];

    NSError *error;
    NSArray *items = [_managedObjectContext executeFetchRequest:fetchRequest error:&error]; 

    for (NSManagedObject *managedObject in items) {
        [_managedObjectContext deleteObject:managedObject];
        NSLog(@"%@ object deleted",entityDescription);
    }
    if (![_managedObjectContext save:&error]) {
        NSLog(@"Error deleting %@ - error:%@",entityDescription,error);

        return NO;
    }
    return YES;
}

- (NSString*)sharedDocumentsPath {
    static NSString *SharedDocumentsPath = nil;
    if (SharedDocumentsPath)
        return SharedDocumentsPath;

    // Compose a path to the <Library>/Database directory
    NSString *libraryPath = [NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES) objectAtIndex:0];
    SharedDocumentsPath = [libraryPath stringByAppendingPathComponent:@"Database"];

    // Ensure the database directory exists
    NSFileManager *manager = [NSFileManager defaultManager];
    BOOL isDirectory;
    if (![manager fileExistsAtPath:SharedDocumentsPath isDirectory:&isDirectory] || !isDirectory) {
        NSError *error = nil;
        NSDictionary *attr = [NSDictionary dictionaryWithObject:NSFileProtectionComplete
                                 forKey:NSFileProtectionKey];
        [manager createDirectoryAtPath:SharedDocumentsPath
           withIntermediateDirectories:YES
                    attributes:attr
                     error:&error];
        if (error)
            NSLog(@"Error creating directory path: %@", [error localizedDescription]);
    }

    return SharedDocumentsPath;
}

- (NSManagedObjectContext*)managedObjectContext {
    if (_managedObjectContext) {
        return _managedObjectContext;
    }
    _managedObjectContext = [[NSManagedObjectContext alloc] init];
    NSUndoManager *undoManager = [[NSUndoManager alloc] init];
    [_managedObjectContext setUndoManager:undoManager];
    [_managedObjectContext setPersistentStoreCoordinator:self.persistentStoreCoordinator];
    [_mainObjectContext setRetainsRegisteredObjects:YES];

    return _managedObjectContext;
}

@end

```

However, in the `managedObjectContext` if I add

```
NSUndoManager *undoManager = [[NSUndoManager alloc] init];
[_managedObjectContext setUndoManager:undoManager];

```

it will crash. 

*Crittercism* logs show

SIGBUS  

main (main.m:16)

```
0    CoreData 0x0033d940 -[NSManagedObject(_NSInternalMethods) _newSnapshotForUndo__] + 352
1    CoreData 0x00318fb1 -[NSManagedObjectContext(_NSInternalChangeProcessing) _registerUndoForOperation:withObjects:withExtraArguments:] + 193
2    CoreData 0x0031922f -[NSManagedObjectContext(_NSInternalChangeProcessing) _registerUndoForInsertedObjects:] + 63
3    CoreData 0x003148f8 -[NSManagedObjectContext(_NSInternalChangeProcessing) _processRecentChanges:] + 1384
4    CoreData 0x00314389 -[NSManagedObjectContext processPendingChanges] + 41
5    CoreData 0x002e8bd8 _performRunLoopAction + 216
6    CoreFoundation 0x0177d99e __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 30
7    CoreFoundation 0x01714640 __CFRunLoopDoObservers + 384
8    CoreFoundation 0x016e04c6 __CFRunLoopRun + 1174
9    CoreFoundation 0x016dfd84 CFRunLoopRunSpecific + 212
10   CoreFoundation 0x016dfc9b CFRunLoopRunInMode + 123
11   GraphicsServices 0x023617d8 GSEventRunModal + 190
12   GraphicsServices 0x0236188a GSEventRun + 103
13   UIKit 0x007e2626 UIApplicationMain + 1163
14   My-App 0x284d main (main.m:16)
15   My-App 0x27b5 start + 53

```

Why is it crashing with these 2 lines when alot of SO posts say to use it? If I take these 2 lines out it won't crash, I am just not able to use undo manager.