Errata for Core Data (2nd edition)

#51137: NSManagedObjectContext ... Therefor, we hand off the reference to it to our AppDelegate so the the rest of the application can access it.

This is great but in the examples you don't do this.

//
// PPRAppDelegate.h
// PPRecipes
//
// Created by Marcus Zarra on 4/3/12.
// Copyright (c) 2012 The Pragmatic Programmer. All rights reserved.
//

@interface PPRAppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;

- (void)saveContext;

@end

--- and part of the .m file

#import "PPRAppDelegate.h"

#import "PPRMasterViewController.h"
#import "PPRImportOperation.h"

@interface PPRAppDelegate()

@property (nonatomic, strong) NSManagedObjectContext *managedObjectContext;

@property (nonatomic, strong) NSURL *fileToOpenURL;

- (void)initializeCoreDataStack;
- (void)contextInitialized;

- (void)consumeIncomingFileURL:(NSURL*)url;

@end

@implementation PPRAppDelegate

@synthesize window;
@synthesize managedObjectContext;
@synthesize fileToOpenURL;

I'm use MVCS and the store needs access to the moc I recommend something like this: in the .h

#define ApplicationDelegate ((AppDelegate *)[UIApplication sharedApplication].delegate)

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;

// Notice how this is called mainManagedObjectContext all the local instances are called
// ManagedObjectContext this is because core data is not thread safe and each access into it needs to be on the thread that calls it.
@property (strong, nonatomic) NSManagedObjectContext *mainManagedObjectContext;

//This is new it is thread safe
- (void)saveContext;

and in .m change to:

@interface AppDelegate()

//Place the private methods in this category
- (void)initializeCoreDataStack;
- (void)contextInitialized;

@end

#pragma mark - Core Data stack

- (void)initializeCoreDataStack
{
NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"GAIGAgent"
withExtension:@"momd"];
ZAssert(modelURL, @"Failed to find model URL");

NSManagedObjectModel *mom = nil;
mom = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
ZAssert(mom, @"Failed to initialize model");

NSPersistentStoreCoordinator *psc = nil;
psc = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:mom];
ZAssert(psc, @"Failed to initialize persistent store coordinator");

NSManagedObjectContext *moc = nil;
NSManagedObjectContextConcurrencyType ccType = NSMainQueueConcurrencyType;
moc = [[NSManagedObjectContext alloc] initWithConcurrencyType:ccType];
[moc setPersistentStoreCoordinator:psc];
//[self setManagedObjectContext:moc];
self.mainManagedObjectContext = moc;

...

so basically make the mainManagedObjectContext accessible so the rest of the app can use it.

The way you have it does work when you set the mod up in the didFinishLaunchingWithOptions but this is not usable when using the MVCS pattern were all the data goes thru the store and thus the store needs access to the "main" moc

--Dave Koz

#50503: These two lines are not correct:

NSArray *newArray = [NSArray arrayWithObject:newIndexPath];
NSArray *oldArray = [NSArray arrayWithObject:indexPath];

arrayWithObject raises an error if its argument is nil, which both of these can be depending upon the mutation type.
--Pete Hopkins

#50838: finalPredicate never declared either in the class or within the local method scope. You might want to check the code being posted on media.pragprog.com too.--Anson Chen

#50502: The creation of the UIAlertView is done within the dispatch_async block on the global queue, which causes an error. It should be done on a block that's run on the main UI queue.--Pete Hopkins

#51215: Book describes

5.5 Parent-Child NSManagedObjectContext Instances
With the release of iOS 6.0 and Mac OS X 10.8 Mountain Lion, a number of new features have been added to Core Data.

I believe these features were introduced with iOS 5.0 / Mac OS X 10.7. Certainly is seems -performBlock: and -performBlockAndWait: are available in iOS 5.0. I can't provide a link to docs as your form prevents it.--Ian Kershaw