CoreData 并发

Question

我遇到了 CoreData 持久性问题（MagicalRecord 2.2、iOS 7.x） 可以在任何线程上创建和使用主对象：

- (Collection *)collection {

    if (!_collection) {
        [MagicalRecord saveWithBlockAndWait:^(NSManagedObjectContext *localContext) {
            _collection = [Collection MR_createInContext:localContext];
            _collection.creationDate = [NSDate date];
            _collection.collectionDescription = @"";
            _collection.name = [CollectionHelper getNameForUnnamedCollection];
        }];
    }

    return _collection;
}

在任何代码位置，我都可以开始在后台线程中向此集合添加资源：

    if (self.photoSavingBlocksCount == 0) {
        [self beginPhotoSaving];
    }
    self.photoSavingBlocksCount++;
[MagicalRecord saveWithBlock:^(NSManagedObjectContext *localContext) {
    Collection *localCollection = [self.collection MR_inContext:localContext];
    [localCollection addNewResourceForImage:image thumb:thumb gallery:gallery type:RESOURCE_TYPE_IMAGE];
} completion:^(BOOL success, NSError *error) {
    self.photoSavingBlocksCount--;
    if (self.photoSavingBlocksCount == 0) {
        [self endPhotoSaving];
    }
}];

此代码将集合及其资源标记为已上传到服务器：

- (BOOL)markCollectionAsUploaded:(Collection *)collection {
    [MagicalRecord saveWithBlockAndWait:^(NSManagedObjectContext *localContext) {
        Collection *localCollection = [collection MR_inContext:localContext];
        localCollection.uploaded = @YES;
        localCollection.uploadDate = [NSDate date];
    }];
    return YES;
}

此代码工作正常，但如果我在此之前编辑集合，则此代码将失败并且集合不会保存为上传！ 换句话说，在下一次获取时，我将得到 collection.uploaded == @NO!

此代码保存编辑的集合

    [MagicalRecord saveWithBlockAndWait:^(NSManagedObjectContext *localContext) {

            Collection *localCollection = [self.collection MR_inContext:localContext];

            NSSet *set = [NSSet setWithArray:self.deletedResources];

            localCollection.uploaded = @NO;
            localCollection.name = ([fieldName.text length] == 0 || [[fieldName.text stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] length] == 0)
            ? [CollectionHelper getNameForUnnamedCollection]
            : fieldName.text;
            localCollection.collectionDescription = [fieldDescription.text stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];

            for (Resource *resource in set) {
                Resource *localResource = [resource MR_inContext:localContext];
                [CollectionHelper removeResourceFiles:resource];
                [localResource MR_deleteEntity];
            }
        }];

在日志中我看到每个上下文保存的相同图片：

-[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x196e2ee0) → Saving <NSManagedObjectContext (0x196e2ee0): *** UNNAMED ***> on *** BACKGROUND THREAD ***
-[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x196e2ee0) → Save Parents? 1
-[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x196e2ee0) → Save Synchronously? 1
-[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x17d83e30) → Saving <NSManagedObjectContext (0x17d83e30): *** BACKGROUND SAVING (ROOT) ***> on *** BACKGROUND THREAD ***
-[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x17d83e30) → Save Parents? 1
-[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x17d83e30) → Save Synchronously? 1

有人可以告诉我一个适合我的情况来管理 CoreData 对象的方法吗？我将不胜感激。

Answer 1

在您的第一个代码块中，您希望这样做：

- (Collection *)collection {

    if (!_collection) {
        [MagicalRecord saveWithBlockAndWait:^(NSManagedObjectContext *localContext) {
            _collection = [Collection MR_createInContext:localContext];
            _collection.creationDate = [NSDate date];
            _collection.collectionDescription = @"";
            _collection.name = [CollectionHelper getNameForUnnamedCollection];
        }];
    }
    _collection = [_collection MR_inContext:self.context];
    return _collection;
}

当您从保存块返回时，localContext 从内存中被丢弃，您的对象将无法保存。为避免此问题，您应该将这个新对象刷新到本地、寿命更长的上下文中。您可以完全避免这种模式，方法是不使用块并直接保存到更长寿的上下文中。

而且，老实说，我没有阅读问题的其余部分，因为应该首先澄清这一点，以避免出现晦涩的崩溃......