失去理智导致获取核心数据总是返回错误

Question

好的，直奔主题……

这是我第一次使用 Magical Panda 的 Magical Record 我已经关注了来自http://yannickloriot.com/2012/03/magicalrecord-how-to-make-programming-with-core-data-pleasant/的教程

这是我的代码

人.h

@property (nonatomic, retain) NSString * firstname;
@property (nonatomic, retain) NSString * lastname;
@property (nonatomic, retain) NSNumber * age;

AppDelegate.M

@implementation AppDelegate

- (void)dealloc
{
    [_window release];
    [_viewController release];
    [super dealloc];
}

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
     [MagicalRecord setupCoreDataStackWithStoreNamed:@"MyDatabase.sqlite"];
    self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease];
    // Override point for customization after application launch.
    self.viewController = [[JASidePanelController alloc] init];
    self.viewController.shouldDelegateAutorotateToVisiblePanel = NO;
  //  self.viewController = [[[ViewControllerCenter alloc] initWithNibName:@"ViewController" bundle:nil] autorelease];
    self.viewController.centerPanel = [[UINavigationController alloc] initWithRootViewController:[[ViewControllerCenter alloc] init]];

    //UINavigationController *navContorller=[[UINavigationController alloc] initWithRootViewController:self.viewController];
    self.viewController.rightPanel = [[NetraRightWindow alloc] init];
    self.window.rootViewController = self.viewController;
    [self.window makeKeyAndVisible];

    return YES;
}

- (void)applicationWillResignActive:(UIApplication *)application
{
    // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
    // Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
}

- (void)applicationDidEnterBackground:(UIApplication *)application
{


    // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later. 
    // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
}

- (void)applicationWillEnterForeground:(UIApplication *)application
{
    // Called as part of the transition from the background to the inactive state; here you can undo many of the changes made on entering the background.
}

- (void)applicationDidBecomeActive:(UIApplication *)application
{

}

- (void)applicationWillTerminate:(UIApplication *)application
{
     [MagicalRecord cleanUp];
    // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
}

@end

这是我的保存方法：

-(void)fetchRecords{

   NSManagedObjectContext *localContext= [NSManagedObjectContext MR_defaultContext];

    // Create a new Person in the current thread context
    Person *person                          = [Person MR_createInContext:    [NSManagedObjectContext MR_defaultContext]];
    person.firstname                        = @"Test";
    person.lastname                         = @"merdeka123";
    person.age=[NSNumber numberWithInt:123];

    [[NSManagedObjectContext MR_defaultContext] MR_save];
    NSArray *Result=[Person MR_findAll];

    NSLog(@"Result==%@",Result);

结果::

2012-11-25 15:43:38.033 Trip[10491:15e03] Cok==(
    "<Person: 0x866fe40> (entity: Person; id: 0x866e170 <x-coredata://15583C03-3EB4-479B-9EF2-B0BC750FC987/Person/p1> ; data: <fault>)",
    "<Person: 0x866fe80> (entity: Person; id: 0x8670210 <x-coredata://15583C03-3EB4-479B-9EF2-B0BC750FC987/Person/p2> ; data: <fault>)",
    "<Person: 0x81471a0> (entity: Person; id: 0x815c2a0 <x-coredata://15583C03-3EB4-479B-9EF2-B0BC750FC987/Person/p3> ; data: {\n    age = 123;\n    firstname = Test;\n    lastname = merdeka123;\n    time = nil;\n})"
)

为什么总是数据错误？这是魔法记录的问题吗？还是我的代码有问题？

Answer 1

这不是错误 - 它是 Core Data 的一个称为“故障”的功能。这里是Apple's description：

故障会减少您的应用程序消耗的内存量。一种 fault 是一个占位符对象，代表一个托管对象 还没有完全实现，或者是一个集合对象 表示关系：

托管对象故障是适当类的实例，但是 它的持久变量尚未初始化。关系错误 是集合类的子类，表示 关系。故障允许 Core Data 在 对象图。因为一个故障没有实现，一个托管对象故障 消耗更少的内存，并且与故障相关的托管对象不是 完全需要在内存中表示。

如果您想查看每个 Person 对象，则必须专门访问它们。

Answer 2

我在 Magical 唱片中也经常犯错。经过大量的头撞。

[[NSManagedObjectContext defaultContext] saveToPersistentStoreWithCompletion:^(BOOL success, NSError *error) {

if (!success) {

NSLog(@"::: Error saving context :::");

}

}];

现在当你找到所有。通过在调试器中打印来检查对象。

Person *testObject = [Result objectAtIndex:0];
NSLog(@"%@", testObject.firstname);

这应该会在调试器中打印您的结果。