当模型更改时，擦除使用CoreData存储的所有数据 [英] Wipe all data stored with CoreData when the model has changed

问题描述

我有一个应用程序从互联网获取数据，并使用CoreData将其存储在设备中，以获得更流畅的体验。

因为我使用Core Data，时间我的模式更改，应用程序崩溃时，我试图运行它与存储在设备上的以前的数据。什么是最快的方式来检测这种变化，并擦除设备中的所有数据，因为我不介意重新下载所有的。

我看到这个检查是在getter中执行的：

   - （NSPersistentStoreCoordinator *）persistentStoreCoordinator 
  

所以我只需要知道实现擦除整个数据库和重新设置Core Data的方法。回到这个问题，要从我的CoreData存储中删除所有的数据，我决定：简单的删除sqlite数据库文件。所以我只是这样实现 NSPersistentStoreCoordinator ：

   - （NSPersistentStoreCoordinator * ）persistStoreCoordinator {
 
 if（persistentStoreCoordinator！= nil）{
 return persistentStoreCoordinator; 
} 
 
 NSURL * storeUrl = [NSURL fileURLWithPath：[[self applicationDocumentsDirectory] ​​stringByAppendingPathComponent：@myAppName.sqlite]]; 
 
 NSError * error = nil; 
 persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel：[self managedObjectModel]]; 
 if（！[persistentStoreCoordinator addPersistentStoreWithType：NSSQLiteStoreType configuration：nil URL：storeUrl options：nil error：& error]）{
 
 NSLog（@打开数据库时出错再试一次。 
 
 //删除sqlite文件，然后重试
 [[NSFileManager defaultManager] removeItemAtPath：storeUrl.path error：nil]; 
 if（！[persistentStoreCoordinator addPersistentStoreWithType：NSSQLiteStoreType configuration：nil URL：storeUrl options：nil error：& error]）{
 NSLog（@Unresolved error％@，％@，error，[error userInfo]）; 
 abort（）; 
} 
 
 //如果应用程序没有退出，显示警告通知用户数据已被删除
 UIAlertView * alert = [[[UIAlertView alloc] initWithTitle ：@读取数据库时遇到错误，请允许所有数据重新下载。 message：@delegate：nil cancelButtonTitle：@OKotherButtonTitles：nil] autorelease]; 
 [alert show]; 
} 
 
 return persistentStoreCoordinator; 
} 
  

I have an app that fetches data from the internet and uses CoreData to store them in the device, for a smoother experience.

Because I use Core Data, every time my schema changes, the app crashes when I try to run it with the previous data stored on the device. What is the fastest way to detect this change and wipe all the data from the device, since I don't mind redownloading them all. It beats crashing and remapping the schema to the new one (in my case).

I see that this check is performed in the getter:

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator

so I only need to know the methodology to implement for wiping the whole database and seting up Core Data again. Thanks :)

解决方案

Coming back to this question, to delete all the data from my CoreData storage I decided to simple delete the sqlite database file. So I just implemented the NSPersistentStoreCoordinator like this:

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {

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

    NSURL *storeUrl = [NSURL fileURLWithPath: [[self applicationDocumentsDirectory] stringByAppendingPathComponent: @"myAppName.sqlite"]];

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

        NSLog(@"Error opening the database. Deleting the file and trying again.");

        //delete the sqlite file and try again
        [[NSFileManager defaultManager] removeItemAtPath:storeUrl.path error:nil];
        if (![persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeUrl options:nil error:&error]) {
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            abort();
        }

        //if the app did not quit, show the alert to inform the users that the data have been deleted
        UIAlertView *alert = [[[UIAlertView alloc] initWithTitle:@"Error encountered while reading the database. Please allow all the data to download again." message:@"" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil] autorelease];
        [alert show];
    }

    return persistentStoreCoordinator;
}

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