ios - NSManagedObjectContext 保存似乎丢失对象

Question

我正在使用以下代码创建一个对象:

 +(Checkin *) newCheckinWithId:(NSString*) checkinID forVenueId:(NSString *)venueId
{
    NSManagedObjectContext * context = [[AppDelegate sharedInstance] managedObjectContext];
    Checkin *ret = (Checkin *)[NSEntityDescription insertNewObjectForEntityForName:@"Checkin" inManagedObjectContext:context];
    ret.checkinID = checkinID;
    ret.forVenueID = venueId;
    ret.date = [NSDate date];
    NSError * error;
    if(![context save:&error]) {
        NSLog(@"Error saving!!!!!: %@", error.userInfo);
    }
    return ret;
}

并且没有错误，但是在保存之后我再也没有看到那个对象的任何记录。

在这个函数上运行调试器，我看到它在 unprocessedInserts 中有 1 个对象，并且在上下文中的所有内部集合中保存 0 个对象之后(我不确定这是否是预期的。

这是我用来创建我的商店 + 托管对象上下文的代码(我对所有内容都使用 1 个上下文)它基本上全部来 self 发现的堆栈溢出帖子

- (NSManagedObjectModel *)managedObjectModel
{
    if (_managedObjectModel != nil)
    {
        return _managedObjectModel;
    }
    //NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"Model" withExtension:@"momd"];
    //__managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];

    //NSArray *testArray = [[NSBundle mainBundle] URLsForResourcesWithExtension:@"momd"subdirectory:nil];

    NSString *path = [[NSBundle mainBundle] pathForResource:@"Model" ofType:@"momd"];

    if( !path ) path = [[NSBundle mainBundle] pathForResource:@"Model" ofType:@"mom"];

    NSURL *modelURL = [NSURL fileURLWithPath:path];

    _managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];

    //__managedObjectModel = [NSManagedObjectModel mergedModelFromBundles:nil];

    return _managedObjectModel;
}

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
    if((_persistentStoreCoordinator != nil)) {
        return _persistentStoreCoordinator;
    }

    _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel: [self managedObjectModel]];
    NSPersistentStoreCoordinator *psc = _persistentStoreCoordinator;

    // Set up iCloud in another thread:

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        // ** Note: if you adapt this code for your own use, you MUST change this variable:
        NSString *iCloudEnabledAppID = @"[MY APP ID]";

        // ** Note: if you adapt this code for your own use, you should change this variable:
        NSString *dataFileName = @"foursquareaugmentation.sqlite";

        // ** Note: For basic usage you shouldn't need to change anything else

        NSString *iCloudDataDirectoryName = @"Data.nosync";
        NSString *iCloudLogsDirectoryName = @"Logs";
        NSFileManager *fileManager = [NSFileManager defaultManager];
        NSURL *localStore = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:dataFileName];
        NSURL *iCloud = [fileManager URLForUbiquityContainerIdentifier:nil];

        if (iCloud) {

            NSLog(@"iCloud is working");

            NSURL *iCloudLogsPath = [NSURL fileURLWithPath:[[iCloud path] stringByAppendingPathComponent:iCloudLogsDirectoryName]];

            NSLog(@"iCloudEnabledAppID = %@",iCloudEnabledAppID);
            NSLog(@"dataFileName = %@", dataFileName);
            NSLog(@"iCloudDataDirectoryName = %@", iCloudDataDirectoryName);
            NSLog(@"iCloudLogsDirectoryName = %@", iCloudLogsDirectoryName);
            NSLog(@"iCloud = %@", iCloud);
            NSLog(@"iCloudLogsPath = %@", iCloudLogsPath);

            if([fileManager fileExistsAtPath:[[iCloud path] stringByAppendingPathComponent:iCloudDataDirectoryName]] == NO) {
                NSError *fileSystemError;
                [fileManager createDirectoryAtPath:[[iCloud path] stringByAppendingPathComponent:iCloudDataDirectoryName]
                       withIntermediateDirectories:YES
                                        attributes:nil
                                             error:&fileSystemError];
                if(fileSystemError != nil) {
                    NSLog(@"Error creating database directory %@", fileSystemError);
                }
            }

            NSString *iCloudData = [[[iCloud path]
                                     stringByAppendingPathComponent:iCloudDataDirectoryName]
                                    stringByAppendingPathComponent:dataFileName];

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

            NSMutableDictionary *options = [NSMutableDictionary dictionary];
            [options setObject:[NSNumber numberWithBool:YES] forKey:NSMigratePersistentStoresAutomaticallyOption];
            [options setObject:[NSNumber numberWithBool:YES] forKey:NSInferMappingModelAutomaticallyOption];
            [options setObject:iCloudEnabledAppID            forKey:NSPersistentStoreUbiquitousContentNameKey];
            [options setObject:iCloudLogsPath                forKey:NSPersistentStoreUbiquitousContentURLKey];

            [psc lock];
            NSError *error;

            [psc addPersistentStoreWithType:NSSQLiteStoreType
                              configuration:nil
                                        URL:[NSURL fileURLWithPath:iCloudData]
                                    options:options
                                      error:&error];

            if( error )
            {
                NSLog(@"Error adding persistent store %@, %@", error, [error userInfo]);

                // comment in this line while debugging if get "Can't find model for source store" error in addPersistentStoreWithType.
                // it means the sqlite database doesn't match the new model and needs to be created from scratch.
                // this happens if you change the xcdatamodel instead of creating a new one under Xcode->Editor->Add Model Version...
                // CoreData can only automatically migrate if there is a new model version (it can't migrate if the model simply changes, because it can't see the difference between the two models).
                // be sure to back up the database if needed, because all data will be lost.
                //[fileManager removeItemAtPath:iCloudData error:&error];

                /*// this is another way to verify the hashes for the database's model to make sure they match one of the entries in the momd directory's VersionInfo.plist
                 NSDictionary *sourceMetadata = [NSPersistentStoreCoordinator metadataForPersistentStoreOfType:NSSQLiteStoreType URL:[NSURL fileURLWithPath:iCloudData] error:&error];

                 if( !sourceMetadata )
                 NSLog(@"sourceMetadata is nil");
                 else
                 NSLog(@"sourceMetadata is %@", sourceMetadata);*/
            }

            [psc unlock];
        }
        else {
            NSLog(@"iCloud is NOT working - using a local store");
            NSMutableDictionary *options = [NSMutableDictionary dictionary];
            [options setObject:[NSNumber numberWithBool:YES] forKey:NSMigratePersistentStoresAutomaticallyOption];
            [options setObject:[NSNumber numberWithBool:YES] forKey:NSInferMappingModelAutomaticallyOption];

            [psc lock];
            NSError *error;

            [psc addPersistentStoreWithType:NSSQLiteStoreType
                              configuration:nil
                                        URL:localStore
                                    options:options
                                      error:nil];

            if( error )
                NSLog(@"Error adding persistent store %@, %@", error, [error userInfo]);
            [psc unlock];
        }

        dispatch_async(dispatch_get_main_queue(), ^{
            [[NSNotificationCenter defaultCenter] postNotificationName:@"SomethingChanged" object:self userInfo:nil];
        });
    });

    return _persistentStoreCoordinator;   
}

/*
 Returns the managed object context for the application.
 If the context doesn't already exist, it is created and bound to the persistent store coordinator for the application.
 */
- (NSManagedObjectContext *) managedObjectContext
{
    if (_managedObjectContext != nil) {
        return _managedObjectContext;
    }

    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (coordinator != nil) {
        _managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
        [_managedObjectContext setPersistentStoreCoordinator: coordinator];
    }
    return _managedObjectContext;
}

我已经在这方面安静地工作了一段时间，并且没有什么可以尝试的，所以任何帮助或调试步骤都将不胜感激。 (它也不适用于 icloud 或本地)

也许我获取错误，这就是我没有获取对象的原因。这是我的提取:

+(NSArray *) checkinsForVenue:(NSString *) venueID
{
    NSManagedObjectContext * context = [[AppDelegate sharedInstance] managedObjectContext];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Checkin" inManagedObjectContext:context];
    NSFetchRequest *request = [[NSFetchRequest alloc] init];
    request.entity = entity;

    //NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(forVenueID = %@)", venueID];
    //request.predicate = predicate;

    NSError *error;
    NSArray * ret = [context executeFetchRequest:request error:&error];
    if(ret == nil) {
        NSLog(@"%@", error.description);
    }
    return ret;
}

编辑:我问错了问题。保存是有效的，提取不是。仍然无法弄清楚我的提取有什么问题。

Answer 1

您是否检查过它是否真的被持久化到 sqlite？

您的应用程序应该在 ~Library/Application Support/iPhone Simulator/6.1/Applications 中。您必须找到属于您的应用程序文件夹(它们都是由 UUIDS 命名的)，然后在 Documents 文件夹中查找 sqlite 文件。在您的代码中，它是 foursquareaugmentation.sqlite。

在该目录中打开终端窗口并启动 sqlite3 foursquareaugmentation.sqlite 以开始查询数据库。

你应该找到一个名为 ZCHECKIN 的表(如果你有一个名为 Checkin 的托管对象类)，并且每次你保存上下文时，它应该添加到那个表。

因此在每次保存后运行 select * from zcheckin; 应该会显示该表中又添加了一行。

如果这没有发生，则 save 操作出现问题。如果它在数据库表中，那么它是您的代码中的某些东西丢失了对该对象的引用，将其设置为 nil 某处，或类似的东西。

希望对您有所帮助。