重置CoreData持久存储 [英] Reset a CoreData persistent store

问题描述

基本上，我想要做的是擦除CoreData持久存储中的所有数据，然后导入新数据。你会怎么做呢？看来最简单的解决方案是调用 [NSPersistentStoreCoordinator removePersistentStore：error：] ，然后删除该文件。这是最好的做法吗？是否是线程安全的？

Basically, what I'm trying to do is to wipe out all data in my CoreData persistent store, then import new data. How would you do this? It seems that the simplest solution is call [NSPersistentStoreCoordinator removePersistentStore:error:] and then remove the file. Is that the best practice available? Is it thread-safe?

非常感谢，

问题0.1：是

Question 0.1: was

我试图更新CoreData持久存储中的数据。我的用户看到一个带有统计数据的表视图。我想通过删除所有现有数据，然后导入新数据来更新应用程序。

I am trying to update the data in a CoreData persistent store. My user is seeing a table view with statistical data. I want to update the application by deleting all existing data, then importing new data. I would like to show a progress view to tell the user that the application is not hanging.

我已经添加了以下 resetPersistentStore 方法在我的AppDelegate（ persistentStoreCoordinator 是为了参考）：

I have added the following resetPersistentStore method in my AppDelegate (persistentStoreCoordinatoris given for reference):

// ...
@property (nonatomic, retain, readonly) NSManagedObjectModel *managedObjectModel;
@property (nonatomic, retain, readonly) NSManagedObjectContext *managedObjectContext;
@property (nonatomic, retain, readonly) NSPersistentStoreCoordinator *persistentStoreCoordinator;
// ...

/**
 Returns the persistent store coordinator for the application.
 If the coordinator doesn't already exist, it is created and the application's store added to it.
 */
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {

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

    NSURL *storeUrl = [NSURL fileURLWithPath: [[self applicationDocumentsDirectory] stringByAppendingPathComponent: kPersistentStoreFilename]];

    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;
}

/**
 * Will remove the persistent store
 */
- (NSPersistentStoreCoordinator *)resetPersistentStore {
    NSError *error;

    [managedObjectContext lock];

    // FIXME: dirty. If there are many stores...
    NSPersistentStore *store = [[persistentStoreCoordinator persistentStores] objectAtIndex:0];

    if (![persistentStoreCoordinator removePersistentStore:store error:&error]) {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }  

    // Delete file
    if (![[NSFileManager defaultManager] removeItemAtPath:store.URL.path error:&error]) {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    } 

    // Delete the reference to non-existing store
    [persistentStoreCoordinator release];
    persistentStoreCoordinator = nil;

    NSPersistentStoreCoordinator *r = [self persistentStoreCoordinator];
    [managedObjectContext unlock];

    return r;
}

然后在我看来， c $ c> MBProgressHUD ：

Then in my view I do (in another thread since I am using MBProgressHUD:

PatrimoineAppDelegate *appDelegate = (PatrimoineAppDelegate *)[[UIApplication sharedApplication] delegate]; 
// Delete everything
[appDelegate resetPersistentStore];

我得到一个 EXC_BAD_ACESS ...

我不知道CoreData或多线程非常好，也许我在做一个明显的错误...

I do not know CoreData or multithreading very well, maybe I'm doing an evident error...

推荐答案

如果你的目标是清空数据存储并重新加载新的信息，更好地使用NSManagedObjectContext的 reset ，然后加载到新数据中。

If your goal is to empty the data store and reload it with new information, you may be better off using NSManagedObjectContext's reset and then loading in new data.

从 NSManagedObjectContext的文档

上下文总是具有父持久存储协调器，其提供模型并向包含数据的各种持久性存储分派请求。没有协调器，上下文不能完全运行。上下文的协调器提供受管对象模型并处理持久性。从外部存储获取的所有对象都与上下文一起注册，该全局标识符（NSManagedObjectID的一个实例）用于唯一标识外部存储的每个对象。

A context always has a "parent" persistent store coordinator which provides the model and dispatches requests to the various persistent stores containing the data. Without a coordinator, a context is not fully functional. The context’s coordinator provides the managed object model and handles persistency. All objects fetched from an external store are registered in a context together with a global identifier (an instance of NSManagedObjectID) that’s used to uniquely identify each object to the external store.

删除持久存储并使用与存储相关联的托管对象上下文可能是错误的原因。

Removing the persistent store and using the managed object context associated with the store is probably the cause of the error.

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