An Objective-C port of my swift 2.0 core data stack(https://gist.github.com/sjgroomi/dcb3fbd11cc09686e685) which was based on Marcus Zarra's example (http://martiancraft.com/blog/2015/03/core-data-stack/)

SGCoreDataStore.h

//
//  SGCoreDataStore.h
//  Core Data Example
//
//  Created by Groom, Stephen on 10/07/2015.
//  Copyright © 2015 Stephen Groom. All rights reserved.
//

@import CoreData;

extern __nonnull NSString *const SGCoreDataStoreErrorDomain;

typedef NS_ENUM(NSUInteger, SGCoreDataStoreError)
{
    SGCoreDataStoreErrorInvalidModelURL
};

@interface SGCoreDataStore : NSObject

/**
 *  For reading on the main thread only
 */
@property (nonatomic, strong, nonnull) NSManagedObjectContext *mainContext;
/**
 *  For all write operations and fetches which can be performed asynchronously
 */
@property (nonatomic, strong, nonnull) NSManagedObjectContext *backgroundContext;

/**
 *  Attempts to create and return a Core Data Store
 *
 *  @param modelURL The URL of the .mom or .momd file
 *  @param storeURL The URL used to create or read the SQLite store
 *  @param error    Will be populated with an underlying error if the store fails to initalize
 *
 *  @return A SGCoreDataStore instance
 */
- (nullable instancetype)initWithModelURL:(nonnull NSURL *)modelURL
                                 storeURL:(nonnull NSURL *)storeURL
                                    error:(NSError **)error;

/**
 *  Saves changes to all managed object contexts in the logical correct order
 *
 *  @param error A NSError** which is populated if there is an error at any point during the save process
 *
 *  @warning This method is thread save but blocks until save operations have completed so avoid calling on the main thread
 */
- (void)save:(NSError **)error;

@end

SGCoreDataStore.m

//
//  SGCoreDataStore.m
//  Core Data Example
//
//  Created by Groom, Stephen on 10/07/2015.
//  Copyright © 2015 Stephen Groom. All rights reserved.
//

#import "SGCoreDataStore.h"

NSString *const SGCoreDataStoreErrorDomain = @"SGCoreDataStoreErrorDomain";

@interface SGCoreDataStore ()
@property (nonatomic, strong) NSManagedObjectContext *privateContext;

@end

@implementation SGCoreDataStore

- (nullable instancetype)initWithModelURL:(nonnull NSURL *)modelURL
                                 storeURL:(nonnull NSURL *)storeURL
                                    error:(NSError **)error
{
    NSManagedObjectModel *objectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
    if (!objectModel)
    {
        if (error != NULL)
        {
            *error = [NSError errorWithDomain:SGCoreDataStoreErrorDomain code:SGCoreDataStoreErrorInvalidModelURL userInfo:nil];
        }
        return nil;
    }
    
    NSPersistentStoreCoordinator *persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:objectModel];
    if (![persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType
                                                  configuration:nil
                                                            URL:storeURL
                                                        options:@{NSInferMappingModelAutomaticallyOption : @(YES),
                                                                  NSMigratePersistentStoresAutomaticallyOption : @(YES)}
                                                          error:error])
    {
        return nil;
    }
    
    self = [super init];
    
    if (self)
    {
        _privateContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
        _privateContext.persistentStoreCoordinator = persistentStoreCoordinator;
        
        _mainContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
        _mainContext.parentContext = _privateContext;
        
        _backgroundContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
        _backgroundContext.parentContext = _mainContext;
    }
    
    return self;
}

- (void)save:(NSError **)error
{
    __block NSError *localError = nil;
    __weak typeof(self) weakSelf = self;
    [self.backgroundContext performBlockAndWait:^{
        [weakSelf.backgroundContext save:&localError];
    }];
    if (!localError)
    {
        [self.mainContext performBlockAndWait:^{
            [weakSelf.mainContext save:&localError];
        }];
    }
    if (!localError)
    {
        [self.privateContext performBlockAndWait:^{
            [weakSelf.privateContext save:&localError];
        }];
    }
    
    if (error)
    {
        *error = localError;
    }
}

@end