使用Magic Record在单独的线程上保存核心数据

Question

我正在使用魔法记录来帮助核心数据保存和多线程.

我用GCD开始一个新线程.在那个新线程中,我检查一个实体是否存在; 如果不是,我想创建一个新的并保存.

saveUsingCurrentThreadContextWithBlock^(NSManagedObjectContext *localContext){}如果在非主线程上调用它,将返回主线程保存吗？

或者我应该将上下文传递给新线程？

编辑:

在主线程上,我创建一个MBProgress指标并创建一个新线程:

MBProgressHUD *HUD = [MBProgressHUD showHUDAddedTo:self.mapView animated:YES];

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{

    Person *person = [Person MR_findFirstByAttribute:NAME withValue:self.user.username];

    if (person == NULL) {
        NSLog(@"SEPERATE THREAD | person %@ does not exist, creating", self.user.username);
        person = [Person MR_createEntity];
        person.name = self.user.username;
        person.uid = self.user.UID;

        [[NSManagedObjectContext MR_contextForCurrentThread] MR_saveOnlySelfWithCompletion:^(BOOL success, NSError *error) {
            [MBProgressHUD hideHUDForView:self.mapView animated:YES];

            Person *person = [Person MR_findFirstByAttribute:NAME withValue:self.user.username];

            if (person) {
                NSLog(@"COMPLETION BLOCK | person exists: %@", person.name);
            }
        }];
    }
    else {
        NSLog(@"SEPERATE THREAD | person %@ does", self.user.username);

            dispatch_async(dispatch_get_main_queue(), ^{
                [MBProgressHUD hideHUDForView:self.mapView animated:YES];
            });
    }
});

(这种保存方法不是持久性,我重启应用程序而我找不到Person实体):

2013-03-12 14:25:44.014  SEPERATE THREAD | person iDealer does not exist, creating
2013-03-12 14:25:44.014  SEPERATE THREAD | thread: <NSThread: 0x84ca720>{name = (null), num = 4}
2013-03-12 14:25:44.015  -[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x840ec30) ? Saving <NSManagedObjectContext (0x840ec30): *** UNNAMED ***> on *** BACKGROUND THREAD ***
2013-03-12 14:25:44.015  -[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x840ec30) ? Save Parents? 0
2013-03-12 14:25:44.015  -[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x840ec30) ? Save Synchronously? 0
2013-03-12 14:25:44.016  -[NSManagedObjectContext(MagicalRecord) MR_contextWillSave:](0x840ec30) Context UNNAMED is about to save. Obtaining permanent IDs for new 1 inserted objects
2013-03-12 14:25:44.132  __70-[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:]_block_invoke21(0x840ec30) ? Finished saving: <NSManagedObjectContext (0x840ec30): *** UNNAMED ***> on *** BACKGROUND THREAD ***
2013-03-12 14:25:44.134  COMPLETION BLOCK | thread: <NSThread: 0x8435f30>{name = (null), num = 1}
2013-03-12 14:25:44.134  COMPLETION BLOCK | person exists: iDealer

Answer 1

好的,我让它上班了:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    Person *person = [Person MR_findFirstByAttribute:NAME withValue:self.user.username];

    if (person == NULL) {
            [MagicalRecord saveUsingCurrentThreadContextWithBlock:^(NSManagedObjectContext *localContext){
                Person *localPerson = [Person MR_createInContext:localContext];
                localPerson.name = self.user.username;

            } completion:^(BOOL success, NSError *error){
                [MBProgressHUD hideHUDForView:self.mapView animated:YES];
            }];
    }
    else {
        dispatch_async(dispatch_get_main_queue(), ^{
            [MBProgressHUD hideHUDForView:self.mapView animated:YES];
        });
    }
});

这可以保存.我不确定这种方法对casademora的意义是不正确的.我无法确定使用此方法与使用saveOnlySelf:completion:方法之间的区别.

似乎我永远无法将上下文保存到持久性存储中saveOnlySelf.如果我用我的问题中的代码创建它,它将被放置在上下文中.如果我搜索了Person实体,我就能找到它.但是一旦我终止了应用程序并重新启动,该Person实体就不会存在.感觉就像是在保存或合并线程上下文到主/默认上下文,但是没有保存上下文.

编辑:

在更多地使用MR之后,似乎如果saveOnlySelf在非主线程中使用任何方法,它将将本地上下文合并到默认上下文,但它不会将其保存到持久性存储.如果在完成后检查默认上下文,则新实体确实存在.但是一旦你终止应用程序并重新运行它,它就不存在了.

要合并上下文并保存到商店,您需要调用其中一种saveToPersistentStoreAndWait类型方法.