ios - 这是拥有CoreData NSFetchedResults和NSPersistentStore函数的正确方法吗？

Question

我一直试图将预先填充的数据库加载到设备中，我尝试从模拟器目录复制数据库并将其放置到应用程序文件夹中，但是它不起作用，所以我想知道我的NSFetchedResultsController是否可以正确获取天气？

- (NSFetchedResultsController *)fetchedResultsController {

    if (fetchedResultsController_ != nil) {
        return fetchedResultsController_;
    }

    CoreDataMelakaAppDelegate *appDelegate = (CoreDataMelakaAppDelegate *)[[UIApplication sharedApplication] delegate];
    NSManagedObjectContext *context = [appDelegate managedObjectContext];
    // Create the fetch request for the entity.
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    // Edit the entity name as appropriate.
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"WhereTo" inManagedObjectContext:context];
    [fetchRequest setEntity:entity];

    // Set the batch size to a suitable number.
   // [fetchRequest setFetchBatchSize:20];

    // Edit the sort key as appropriate.
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:NO];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];

    [fetchRequest setSortDescriptors:sortDescriptors];

    // Edit the section name key path and cache name if appropriate.
    // nil for section name key path means "no sections".
    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:@"Root"];
    aFetchedResultsController.delegate = self;
    self.fetchedResultsController = aFetchedResultsController;

    [aFetchedResultsController release];
    [fetchRequest release];
    [sortDescriptor release];
    [sortDescriptors release];

    NSError *error = nil;
    if (![fetchedResultsController_ performFetch:&error]) {
        /*
         Replace this implementation with code to handle the error appropriately.

         abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. If it is not possible to recover from the error, display an alert panel that instructs the user to quit the application by pressing the Home button.
         */
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }

    return fetchedResultsController_;
}    

持久存储

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {

    if (persistentStoreCoordinator_ != nil) {
        return persistentStoreCoordinator_;
    }

    NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"CoreDataMelaka.sqlite"];

    NSError *error = nil;
    persistentStoreCoordinator_ = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
    if (![persistentStoreCoordinator_ addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {
        /*
         Replace this implementation with code to handle the error appropriately.

         abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. If it is not possible to recover from the error, display an alert panel that instructs the user to quit the application by pressing the Home button.

         Typical reasons for an error here include:
         * The persistent store is not accessible;
         * The schema for the persistent store is incompatible with current managed object model.
         Check the error message to determine what the actual problem was.


         If the persistent store is not accessible, there is typically something wrong with the file path. Often, a file URL is pointing into the application's resources directory instead of a writeable directory.

         If you encounter schema incompatibility errors during development, you can reduce their frequency by:
         * Simply deleting the existing store:
         [[NSFileManager defaultManager] removeItemAtURL:storeURL error:nil]

         * Performing automatic lightweight migration by passing the following dictionary as the options parameter: 
         [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithBool:YES],NSMigratePersistentStoresAutomaticallyOption, [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];

         Lightweight migration will only work for a limited set of schema changes; consult "Core Data Model Versioning and Data Migration Programming Guide" for details.

         */
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }    

    return persistentStoreCoordinator_;
}

我已经用这个替换了persistentStore，现在我从模拟器中删除数据库或应用程序的方式都显示为2个数据，这是我第一次尝试此方法时安装的。

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {

    if (persistentStoreCoordinator_ != nil) {
        return persistentStoreCoordinator_;
    }

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *writableDBPath = [documentsDirectory stringByAppendingPathComponent:@"CoreDataMelaka.sqlite"];

    NSString *storePath = [[NSBundle mainBundle] pathForResource:@"CoreDataMelaka" ofType:@"sqlite"];


    NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"CoreDataMelaka.sqlite"]; 

    NSLog(@"store URL %@", storeURL);

    // Put down default db if it doesn't already exist
    NSFileManager *fileManager = [NSFileManager defaultManager];
    if (![fileManager fileExistsAtPath:writableDBPath]) {
        NSLog(@"proceed");
        NSString *defaultStorePath = [[NSBundle mainBundle] pathForResource:@"CoreDataMelaka" ofType:@"sqlite"];
        NSLog(@"doesnt exist");
        NSLog(@"defalultStorePath %@", defaultStorePath);


        if (defaultStorePath) {
            [fileManager copyItemAtPath:defaultStorePath toPath:writableDBPath error:NULL];
            NSLog(@"storePath= %@", storePath);
        }
    }    

    NSError *error = nil;
    persistentStoreCoordinator_ = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
    if (![persistentStoreCoordinator_ addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {

        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }    

    return persistentStoreCoordinator_;
}

Answer 1

您的NSFetchedResultsController看起来像标准的自动生成的代码。它应该可以正确获取，但是我需要更多地了解您的代码以确保100％正确。

我猜想这个问题与查找数据库有关。您确定要把它放在文件目录中吗？我假设您已将数据库复制到Xcode中，并且正在将数据库复制到您的应用程序中。在这种情况下，您的数据库将不在您的Documents目录中。您可以使用Xcode中管理器的“设备”部分下载应用程序文件以确认这一点。您的数据库已复制到您的主捆绑包中，您需要从那里提取它。这是一些执行此操作的代码:

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {

    if (__persistentStoreCoordinator != nil)
        return __persistentStoreCoordinator;

    NSError * error = nil;
    NSURL * storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"Store.sqlite"];
    NSFileManager * fileManager = [NSFileManager new];

    // !!!: Be sure to create a new default database if the MOM file is ever changed.

    // If there is no previous database, then a default one is used.
    if (![fileManager fileExistsAtPath:storePath]) {

        NSURL * defaultStoreURL = [[NSBundle mainBundle] URLForResource:@"DefaultStore.sqlite" 
                                                          withExtension:nil];

        // Copies the default database from the main bundle to the documents directory.
        [fileManager copyItemAtURL:defaultStoreURL
                             toURL:storeURL
                             error:&error];

        if (error) {

            // Handle error here.

            // Resets the error.
            error = nil;
        }
    }

    [fileManager release];

    __persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];

    [__persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType 
                                           configuration:nil 
                                                     URL:storeURL 
                                                 options:nil 
                                                   error:&error];
    if (error) {

        // Handle error here.

        abort();
    }    

    return __persistentStoreCoordinator;
}

要找到此便利和其他Core Data便利，请查看 RBCoreDataAdditions。