在 for 循环中传递数据时，MagicalRecord 正在保存 null

Posted 2023-03-04

【中文标题】在 for 循环中传递数据时，MagicalRecord 正在保存 null

【英文标题】：MagicalRecord is saving null when passed data inside a for loop

【发布时间】：2014-03-28 11:03:31

【问题描述】：

我正在使用AFNetworking 来调用Web 服务所有下拉数据。数据被放入responseobject，然后我试图放入CoreData。

由于某种原因，数据未存储到CoreData 实体中。我的代码：

    for (int i = 0; i < [[responseObject valueForKey:@"belief"] count]; i++) 

        NSString * topicID = [[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"_id"];
        NSString * title = [[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"title"];
        NSString * body = [[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"body"];
        NSString * category = [[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"category"];
        NSNumber * nFor = @([[[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"nFor"] intValue]);

        NSLog(@"Title being sent is %@",title);
        NSLog(@"Number of votes sent is %@",nFor);

        ExploreCD *exploreCD = [ExploreCD MR_createEntity];
        exploreCD.topicID = topicID;
        exploreCD.title = title;
        exploreCD.body = body;
        exploreCD.category = category;
        exploreCD.nFor = nFor;

        NSLog(@"Title being saved is %@",exploreCD.title);
        NSLog(@"Number of votes saved is %@",exploreCD.nFor);

        //[NSManagedObjectContext MR_contextForCurrentThread];
    

这是我的代码中的NSLogs 正在读出的内容。任何帮助将不胜感激

2014-03-28 18:49:39.677 Karmo[8328:60b] Title being sent is a odio in
2014-03-28 18:49:39.677 Karmo[8328:60b] Number of votes sent is 0
2014-03-28 18:49:39.677 Karmo[8328:60b] Title being saved is (null)
2014-03-28 18:49:39.677 Karmo[8328:60b] Number of votes saved is (null)
2014-03-28 18:49:39.678 Karmo[8328:60b] Title being sent is amet nunc viverra dapibus
2014-03-28 18:49:39.678 Karmo[8328:60b] Number of votes sent is 0
2014-03-28 18:49:39.678 Karmo[8328:60b] Title being saved is (null)
2014-03-28 18:49:39.678 Karmo[8328:60b] Number of votes saved is (null)
2014-03-28 18:49:39.678 Karmo[8328:60b] Title being sent is semper sapien a libero nam
2014-03-28 18:49:39.678 Karmo[8328:60b] Number of votes sent is 2
2014-03-28 18:49:39.678 Karmo[8328:60b] Title being saved is (null)
2014-03-28 18:49:39.678 Karmo[8328:60b] Number of votes saved is (null)
2014-03-28 18:49:39.679 Karmo[8328:60b] -[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x109346550) NO CHANGES IN ** DEFAULT ** CONTEXT - NOT SAVING

在 afnetworkwing 代码的成功部分中的 for 循环完成后，我将使用此代码保存这些新的 CoreData 实体。

    [MagicalRecord saveUsingCurrentThreadContextWithBlock:nil completion:^(BOOL success, NSError *error) 

        exploreCellData = [[ExploreCD MR_findAll] mutableCopy];

   ];

【问题讨论】：

你有解决办法吗？有什么线索吗？真的很奇怪！

什么都没有……我想不通。我想知道最初的 MagicalRecord 设置是否有问题。因为我遇到的另一个错误是，如果我尝试通过调用 MR_truncateAll 方法清除数据，我的应用程序也会崩溃。

您将这段代码保存在哪里？

@user2939977 是的，这可能是一种可能性：您的 AppDelegate.m 中的 application:(UIApplication *)application didFinishLaunchingWithOptions: 中有 [MagicalRecord setupCoreDataStack]; 吗？

“我的应用程序也崩溃了”我认为如果您提供崩溃报告会很有帮助。正如@shingo.nakanishi 已经提到的，您需要在导入后保存。

【参考方案1】：

这很正常。您只创建实体，但忘记保存它们！

我认为你可以这样做：

NSManagedObjectContext * context = [NSManagedObjectContext MR_context]; // New context
for (int i = 0; i < [[responseObject valueForKey:@"belief"] count]; i++) 
    NSString * topicID = [[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"_id"];
    NSString * title = [[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"title"];
    NSString * body = [[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"body"];
    NSString * category = [[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"category"];
    NSNumber * nFor = @([[[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"nFor"] intValue]);

    NSLog(@"Title being sent is %@",title);
    NSLog(@"Number of votes sent is %@",nFor);

    ExploreCD *exploreCD = [ExploreCD MR_createEntityInContext:context];
    exploreCD.topicID = topicID;
    exploreCD.title = title;
    exploreCD.body = body;
    exploreCD.category = category;
    exploreCD.nFor = nFor;

    NSLog(@"Title being saved is %@",exploreCD.title);
    NSLog(@"Number of votes saved is %@",exploreCD.nFor);

// Save the datas
[context  MR_saveToPersistentStoreWithCompletion:^(BOOL success, NSError *error) 
    if (!success)
        NSLog(@"Error: %@", [error localizedDescription]);
];

【参考方案2】：

我认为你需要保存。比如saveWithBlock等等。

[MagicalRecord saveWithBlock:^(NSManagedObjectContext *localContext) 
 for (int i = 0; i < [[responseObject valueForKey:@"belief"] count]; i++) 

        NSString * topicID = [[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"_id"];
        NSString * title = [[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"title"];
        NSString * body = [[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"body"];
        NSString * category = [[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"category"];
        NSNumber * nFor = @([[[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"nFor"] intValue]);

        NSLog(@"Title being sent is %@",title);
        NSLog(@"Number of votes sent is %@",nFor);

        ExploreCD *exploreCD = [ExploreCD MR_createInContext:localContext];
        exploreCD.topicID = topicID;
        exploreCD.title = title;
        exploreCD.body = body;
        exploreCD.category = category;
        exploreCD.nFor = nFor;

        NSLog(@"Title being saved is %@",exploreCD.title);
        NSLog(@"Number of votes saved is %@",exploreCD.nFor);

        //[NSManagedObjectContext MR_contextForCurrentThread];
    
];

【讨论】：

感谢您的回复，但我仍然看到上面代码的 (null) 值。

save: 应该在 for 循环之外。不能去save: block里面的for loop！这是肯定的。

而要保存的函数是：NSManagedObjectContext *localContext = [NSManagedObjectContext MR_defaultContext];[localContext MR_saveOnlySelfWithCompletion:^(BOOL success, NSError *error) ... ];

@user2939977 (*ﾟﾛﾟ)哦，我明白了。你的问题ExploreCD 属性总是nil，如果你保存与否。

@Gabriel.Massana 我的英语不好。我想看看你的意思。你的意思是[MagicalRecord saveWithBlock:^(NSManagedObjectContext *localContext) for() [ExploreCD MR_createInContext:localContext]; 是NG。