objective-c - 预加载的核心数据数据库不起作用

Question

我在一个应用程序中创建了一个核心数据数据库，其中涉及从 API 中提取信息并填充数据库。

我现在想在另一个应用程序中使用它。

我已复制 .xcdatamodeld 文件和 NSManagedObject 类。

我已经添加并导入了 Core Data 框架。

我已将 .sqlite 文件复制到新应用程序的资源中作为默认数据库。

我正在使用以下代码，该代码应该将默认数据库复制到文档目录并打开它，以便我可以对其执行查询。

它导致应用程序崩溃，但没有错误消息，您对我哪里出错有什么想法吗？

如果我要使用 saveToURL 在这里创建一个数据库，我知道文件名将是 persistenceStore 而不是 Trailer.sqlite，如下所示，这相关吗？

谢谢

- (void)viewDidLoad
{
[super viewDidLoad];


// Get URL -> "<Documents Directory>/<TrailerDB>" 
NSURL *url = [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];

url = [url URLByAppendingPathComponent:@"TrailerDB"];

UIManagedDocument *doc = [[UIManagedDocument alloc] initWithFileURL:url];

// Copy out default db to documents directory if it doesn't already exist
NSFileManager *fileManager = [NSFileManager defaultManager];

if (![fileManager fileExistsAtPath:[url path]]) {
    NSString *defaultDB = [[NSBundle mainBundle] 
                                  pathForResource:@"trailerdatabase" ofType:@"sqlite"];
    if (defaultDB) {

        [fileManager copyItemAtPath:defaultDB toPath:[url path] error:NULL];

    }
}

if (doc.documentState == UIDocumentStateClosed) {

    // exists on disk, but we need to open it
    [doc openWithCompletionHandler:^(BOOL success) 
     {

         if (success) [self useDatabase:doc];

         if (!success) NSLog(@"couldn’t open document at %@", url);


     }];

} else if (doc.documentState == UIDocumentStateNormal) 
{
    [self useDatabase:doc];
}

}

Answer 1

我又看了一遍，我不确定你在做什么，但下面的代码是我所做的，可以回答你的问题。我检查工作数据库是否存在，如果不存在，我将其从应用程序包中移动到位，然后继续加载它。我留下了苹果模板中的股票评论，因为我认为它们最终可能会有所帮助。

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

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

    NSError *error = nil;

    if (![[NSFileManager defaultManager] fileExistsAtPath:[[self applicationDocumentsDirectoryString] stringByAppendingPathComponent: @"workingDataBase.sqlite"]]){
        //database not detected
        NSLog(@"database not detected");
        NSURL  * defaultDatabase = [NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"DefaultData" ofType:@"sqlite"]];
        NSError * error;
        if (![[NSFileManager defaultManager] copyItemAtURL:defaultDatabase toURL:storeURL error:&error]){
            // Handle Error somehow!
            NSLog(@"copy file error, %@", [error description]);
        }
    }

    __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;
}