正确的方法来刷新Core Data数据库 [英] Correct way to refresh Core Data database

问题描述

我的应用程式已设定好，以便在第一次使用时，从基于网路的xml资讯提供中下载所需的资料。

My app is setup so that when it's first used, it downloads the required data from a web based xml feed.

使用者也可以定期更新

当这样做时，我要删除现有的数据库，然后通过我在第一次加载时使用的代码重新创建它。

When they do this, I want to delete the existing database and then recreate it via the code I use for the first load.

我读到简单地删除数据库不是正确的方法，所以我使用下面的方式来销毁数据，然后加载新的数据集。

I read that simply deleting the database is not the correct way to do this so I'm using the following to destroy the data before loading the new dataset.

- (void)resetApplicationModel {

NSURL *_storeURL = [NSURL fileURLWithPath: [[self applicationDocumentsDirectory] stringByAppendingPathComponent: DBSTORE]];
NSPersistentStore *_store = [persistentStoreCoordinator persistentStoreForURL:_storeURL];
[persistentStoreCoordinator removePersistentStore:_store error:nil];
[[NSFileManager defaultManager] removeItemAtPath:_storeURL.path error:nil];

[persistentStoreCoordinator release], persistentStoreCoordinator = nil;
}

但这不起作用，当执行数据刷新时，数据，但无法将其保存到数据库，并在控制台中生成以下错误：

However this doesn't work, when performing a data refresh, it downloads the data but can't save it to the database and generates the following error in the console;

此NSPersistentStoreCoordinator没有持久存储。

This NSPersistentStoreCoordinator has no persistent stores. It cannot perform a save operation.

刷新资料库的「正确」方法是什么？

What's the "correct" way to refresh a database?

推荐答案

这样做的正确方法是只取出所有对象，删除它们，然后保存上下文。 （http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CoreData/Articles/cdFetching.html）

The "right" way to do this is to just fetch all of the objects, delete each of them, and then save the context. (http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CoreData/Articles/cdFetching.html)

- (void) deleteAllEntitiesForName:(NSString*)entityName {
    NSManagedObjectContext *moc = [self managedObjectContext];
    NSEntityDescription *entityDescription = [NSEntityDescription
        entityForName:entityName inManagedObjectContext:moc];
    NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
    [request setEntity:entityDescription];
    NSError *error = nil;
    NSArray *array = [moc executeFetchRequest:request error:&error];
    if (array != nil) {
        for(NSManagedObject *managedObject in array) {
            [moc deleteObject:managedObject];
        }
        error = nil;
        [moc save:&error];
    }

}

。

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