魔法记录，无法保存对象：contextDidSave == NO，error = nil

Question

我正在尝试保留新实体：

- (void)updateStorageWithQuizzess:(NSArray *)quizzess completion:(void(^)(NSArray *quizzess, BOOL succes, NSError *error))completion {
    NSMutableArray *mutableArray = [NSMutableArray array];

    [Quiz MR_truncateAll];
    [[NSManagedObjectContext MR_context] MR_saveWithBlock:^(NSManagedObjectContext *localContext) {

        for (NSDictionary *dictionary in quizzess) {
            Quiz *quiz = [Quiz MR_createEntity];
            [quiz fromDictionary:dictionary];
            [mutableArray addObject:quiz];
        }
    } completion:^(BOOL contextDidSave, NSError *error) {
        BlockSafeRun(completion, mutableArray, contextDidSave, error);
    }];
}

或者像这样：

- (void)updateStorageWithQuizzess:(NSArray *)quizzess completion:(void(^)(NSArray *quizzess, BOOL succes, NSError *error))completion {
    NSMutableArray *mutableArray = [NSMutableArray array];

    [Quiz MR_truncateAll];

    [MagicalRecord saveWithBlock:^(NSManagedObjectContext *localContext) {
        for (NSDictionary *dictionary in quizzess) {
            Quiz *quiz = [Quiz MR_createEntity];
            [quiz fromDictionary:dictionary];
            [mutableArray addObject:quiz];
        }
    } completion:^(BOOL contextDidSave, NSError *error) {
        BlockSafeRun(completion, mutableArray, contextDidSave, error);
    }];
}

但是在完成块中我收到 contextDidSave == NO，error == nil。所以我不知道出了什么问题。我犯了一些明显的错误吗？我该如何调试该问题？

//////

2015-06-17 20:39:27.061 HITO[6733:618953] Set root saving context: <NSManagedObjectContext: 0x16dbe070>
2015-06-17 20:39:27.062 HITO[6733:618953] Created new main queue context: <NSManagedObjectContext: 0x16e855b0>
2015-06-17 20:39:27.063 HITO[6733:618953] Set default context: <NSManagedObjectContext: 0x16e855b0>
2015-06-17 20:39:27.316 HITO[6733:618953] [HockeySDK] WARNING: Detecting crashes is NOT enabled due to running the app with a debugger attached.
2015-06-17 20:39:28.829 HITO[6733:618953] Created new private queue context: <NSManagedObjectContext: 0x16d57870>
2015-06-17 20:39:28.831 HITO[6733:619027] Created new private queue context: <NSManagedObjectContext: 0x16ea4ec0>
2015-06-17 20:39:28.841 HITO[6733:619027] NO CHANGES IN ** saveWithBlock:completion: ** CONTEXT - NOT SAVING

更新

来自 MR 的以下代码：

- (void) MR_saveWithOptions:(MRSaveOptions)saveOptions completion:(MRSaveCompletionHandler)completion;
{
    __block BOOL hasChanges = NO;

    if ([self concurrencyType] == NSConfinementConcurrencyType)
    {
        hasChanges = [self hasChanges];
    }
    else
    {
        [self performBlockAndWait:^{
            hasChanges = [self hasChanges];
        }];
    }

    if (!hasChanges)
    {
        MRLogVerbose(@"NO CHANGES IN ** %@ ** CONTEXT - NOT SAVING", [self MR_workingName]);

        if (completion)
        {
            dispatch_async(dispatch_get_main_queue(), ^{
                completion(NO, nil);
            });
        }

        return;
    }

所以，有变化 returns NO.

Answer 1

您的对象在保存块中没有发生任何变化。我在这里看到两个问题。

当您需要在 localContext 中创建新对象时，您正在 MR_defaultContext 中创建它们，这是您的保存块的保存上下文。

试试这个：

- (void)updateStorageWithQuizzess:(NSArray *)quizzess completion:(void(^)(NSArray *quizzess, BOOL succes, NSError *error))completion {
    NSMutableArray *mutableArray = [NSMutableArray array];


    [MagicalRecord saveWithBlock:^(NSManagedObjectContext *localContext) {
        for (NSDictionary *dictionary in quizzess) {
            Quiz *quiz = [Quiz MR_createInContext:localContext];
            [quiz fromDictionary:dictionary];
            [mutableArray addObject:quiz];
        }
    } completion:^(BOOL contextDidSave, NSError *error) {
        BlockSafeRun(completion, mutableArray, contextDidSave, error);
    }];
}

在您开始导入新对象之前，您的对象实际上并没有被删除。这可能不会导致您的上下文没有任何变化，但我也会讨论这个问题。

[Quiz MR_truncateAll] 只是将所有 Quiz 对象 deleted属性设置为 true。这意味着下次保存或处理上下文时，将保存更改。

因此，当您创建新的保存上下文时，该上下文仍然包含那些对象。我不确定你的 fromDictionary 方法在做什么，但如果它依赖于数据库，那么它就不会拥有它。

你需要这样做：

- (void)updateStorageWithQuizzess:(NSArray *)quizzess completion:(void(^)(NSArray *quizzess, BOOL succes, NSError *error))completion {
    NSMutableArray *mutableArray = [NSMutableArray array];


    [MagicalRecord saveWithBlock:^(NSManagedObjectContext *localContext) {
        [Quiz MR_truncateAllInContext:localContext];
        [localContext processPendingChanges];

        for (NSDictionary *dictionary in quizzess) {
            Quiz *quiz = [Quiz MR_createInContext:localContext];
            [quiz fromDictionary:dictionary];
            [mutableArray addObject:quiz];
        }
    } completion:^(BOOL contextDidSave, NSError *error) {
        BlockSafeRun(completion, mutableArray, contextDidSave, error);
    }];
}

这样，您将删除保存上下文中的对象。您还必须记住在保存上下文中调用 processPendingChanges 以从上下文中删除对象，而不是仅仅将它们标记为要删除。

魔法记录，无法保存对象：contextDidSave == NO，error = nil

Magical Record, cannot save an object: contextDidSave == NO, error = nil

iphone

core-data

objective-c

ios

magicalrecord