core-data - 硬核数据+iCloud场景

Question

我有一个很难解决的问题。我有这种情况:

我的应用程序使用 CoreData 来存储对象，我想在设备之间实现 iCloud 同步...并且我的应用程序需要一个初始填充的数据库。

我第一次启动我的应用程序时，它会在云端填充我的数据库，并将某些数据库字段标记为"is"，并将其标记为“已安装数据库”。这些字段也在云端同步。

现在，当另一台设备首次启动该应用程序时，我希望检索字段“databaseInstalled”以检查是否注入(inject)了一些数据，但这是错误的...

如果 databaseInstalled 为假，我们注入(inject)数据，如果 databaseInstalled 为真，我们等待 iCloud 同步。

问题是我异步检索了 persistentStoreCoordinator，因为我不想阻止正在等待从 iCloud 下载数据的应用程序...

那么，如果我需要填充数据库，或者它已经在另一台设备上填充，那么我如何才能先验地知道，而我只是从 iCloud 下载填充的那个呢？

- (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 = @"this is a secret!";

        // ** Note: if you adapt this code for your own use, you should change this variable:        
        NSString *dataFileName = @"you do not have to know.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);

            // da rimuovere

            //[fileManager removeItemAtURL:iCloudLogsPath error:nil];
            #warning to remove

            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];

            //[fileManager removeItemAtPath:iCloudData error:nil];
#warning to remove

            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];

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

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

            [psc lock];

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

        }

        dispatch_async(dispatch_get_main_queue(), ^{
            NSLog(@"iCloud routine completed.");

            Setup *install = [[Setup alloc] init];

            if([install shouldMigrate]) {
                HUD = [[MBProgressHUD alloc] initWithView:self.window.rootViewController.view];
                HUD.delegate = self;
                HUD.labelText = NSLocalizedString(@"Sincronizzazione del database", nil);
                [self.window.rootViewController.view addSubview:HUD];
                [HUD showWhileExecuting:@selector(installDatabase) onTarget:install withObject:nil animated:YES];
            }
            else {
                [[NSNotificationCenter defaultCenter] postNotificationName:@"setupCompleted" object:self];
            }

            //[[NSNotificationCenter defaultCenter] postNotificationName:@"icloudCompleted" object:self userInfo:nil];
            [[NSNotificationCenter defaultCenter] postNotificationName:@"setupCompleted" object:self];
        });
    });

    return __persistentStoreCoordinator;
}

Answer 1

在完成与 iCloud 的同步之前，您无法知道 iCloud 中是否会有数据可用。这意味着您有两个选择:

• 让用户等到同步完成。

• 使用您的默认数据库启动并尽可能合并来自 iCloud 的更改。

使用 iCloud，您需要一些 strategy for resolving conflicts本地数据和云数据之间的差异，因为您必须处理用户可能同时更改多个设备上的数据这一事实。准备就绪后，很明显上面的第二个选项是更好的选项:用户可以立即开始使用您的应用程序，并且云中的数据可用时会合并。