保存上下文中的 CoreData 错误，NSPersistentStoreCoordinator 没有持久存储

Question

我已经查看了我能找到的所有类似问题，但他们的解决方案都不适合我。

一个问题可能是，在我返回 JSON 并从 webAPI 解析之后，将实体添加到上下文（成功）和保存上下文发生在不同的线程上。但是上下文是在第一次使用 manageContext 和持久存储时设置的，如下所示。因此，在解析发生这种情况后，它将在该线程上。

确切的错误：

 *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'This NSPersistentStoreCoordinator has no persistent stores.  It cannot perform a save operation.'

我已经尝试从模拟器中删除应用程序，正如建议的那样，没有改变。

这是我正在使用的 CoreDataHelper 类，我的应用程序中只有 1 个实例，当我在将新项目添加到上下文后调用 helper 上的 saveContext 方法时会发生错误：

@implementation CoreDataHelper

@synthesize managedObjectContext = _managedObjectContext;
@synthesize managedObjectModel = _managedObjectModel;
@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;

#pragma mark - Application's Documents directory

// Returns the URL to the application's Documents directory.
- (NSURL *)applicationDocumentsDirectory
{
    return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory
                                                   inDomains:NSUserDomainMask] lastObject];
}

- (void)saveContext
{
    NSError *error = nil;
    if (self.managedObjectContext != nil) {
        if ([self.managedObjectContext hasChanges] && ![self.managedObjectContext save:&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.
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            abort();
        }
    }
}

- (void)dealloc {

    [self saveContext];
}

#pragma mark - Core Data stack

// Returns the managed object context for the application.
// If the context doesn't already exist, it is created and bound to the persistent store coordinator for the application.
- (NSManagedObjectContext *)managedObjectContext
{
    if (_managedObjectContext != nil) {
        return _managedObjectContext;
    }

    NSPersistentStoreCoordinator *coordinator = self.persistentStoreCoordinator;
    if (coordinator != nil) {
        _managedObjectContext = [[NSManagedObjectContext alloc] init];
        [_managedObjectContext setPersistentStoreCoordinator:coordinator];
    }
    return _managedObjectContext;
}

// Returns the managed object model for the application.
// If the model doesn't already exist, it is created from the application's model.
- (NSManagedObjectModel *)managedObjectModel
{
    if (_managedObjectModel != nil) {
        return _managedObjectModel;
    }
    NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"Model" withExtension:@"momd"];
    _managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
    return _managedObjectModel;
}

// 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 = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"UserGroupTV.sqlite"];

    NSError *error = nil;
    _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc]
                                   initWithManagedObjectModel:[self managedObjectModel]];

    // needed for lightweight migrations
    NSMutableDictionary *options = [NSMutableDictionary dictionary];
    [options setObject:[NSNumber numberWithBool:YES]
                forKey:NSMigratePersistentStoresAutomaticallyOption];
    [options setObject:[NSNumber numberWithBool:YES]
                forKey:NSInferMappingModelAutomaticallyOption];

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

        UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"Error"
                                                            message:[error localizedDescription]
                                                           delegate:self
                                                  cancelButtonTitle:@"OK"
                                                  otherButtonTitles:nil, nil];
        [alertView show];
    }

    return _persistentStoreCoordinator;
}


@end

ETA：我已经看到它提到过，但是如何/在哪里删除存储 sql 文件的机器上的本地文件夹？

Answer 1

我没有一个明确的答案，但这里有一些事情要注意：

1. 在您创建persistentStoreCoordinator 的位置添加一些登录信息。如果在创建过程中添加商店时发生错误，您可以在那里捕获它。

2. 您提到您将托管对象上下文保存在后台线程上。 NSManagedObjectContext 不是线程安全的，您应该只在创建它的线程上使用特定的上下文。每个线程至少需要一个上下文。您可以观察“NSManagedObjectContextDidSaveNotification”并将更改合并到您的主要上下文中。

Answer 2

结果我每次调用 Web API 时都在删除商店，而不是重新创建它。我最初的目标是每次用户想通过调用 api 刷新视频列表时清理数据库，我正在删除所有对象，然后删除存储并忘记重新创建它。这是我的刷新数据库方案，我只是删除了 saveContext 调用下的所有内容。

- (void)resetDataBase {

    [self deleteAllObjects:@"Speaker"];
    [self deleteAllObjects:@"Tag"];
    [self deleteAllObjects:@"UserGroup"];
    [self deleteAllObjects:@"Video"];

    [_coreDataHelper saveContext];

    // REMOVED BELOW and it worked
    NSPersistentStore * store = [[_coreDataHelper.persistentStoreCoordinator persistentStores] lastObject];
    if (store) {
        NSError * error;
        [_coreDataHelper.persistentStoreCoordinator removePersistentStore:store error:&error];
        if (error) {
            [self showError:error];
        }
    }

    NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"UserGroupTV.sqlite"];
    [[NSFileManager defaultManager] removeItemAtURL:storeURL error:nil];
}