[对请求更新回复的赏金的响应延迟]

回顾之前的答案，

Fetching and deleting all items, as suggested by @Grouchal and others, is still an effective and useful solution. If you have very large data stores then it might be slow, but it still works very well. Simply removing the data store is, as you and @groundhog note, no longer effective. It's obsolete even if you don't use external binary storage because iOS 7 uses WAL mode for SQLite journalling. With WAL mode there may be (potentially large) journal files sitting around for any Core Data persistent store.

But there's a different, similar approach to removing the persistent store that does work. The key is to put your persistent store file in its own sub-directory that doesn't contain anything else. Don't just stick it in the documents directory (or wherever), create a new sub-directory just for the persistent store. The contents of that directory will end up being the persistent store file, the journal files, and the external binary files. If you want to nuke the entire data store, delete that directory and they'll all disappear.

在设置持久化存储时，你会这样做:

NSURL *storeDirectoryURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"persistent-store"];
if ([[NSFileManager defaultManager] createDirectoryAtURL:storeDirectoryURL
        withIntermediateDirectories:NO
        attributes:nil
        error:nil]) {
    NSURL *storeURL = [storeDirectoryURL URLByAppendingPathComponent:@"MyApp.sqlite"];
    // continue with storeURL as usual...
}

然后当你想把商店搬走的时候，

[[NSFileManager defaultManager] removeItemAtURL:storeDirectoryURL error:nil];

这将递归地删除自定义子目录和其中的所有Core Data文件。

这只在您没有将持久存储与其他重要数据放在同一个文件夹中时才有效。比如documents目录，其中可能有其他有用的东西。如果这是您的情况，您可以通过查找您想要保留的文件并删除所有其他文件来获得相同的效果。喜欢的东西:

NSString *docsDirectoryPath = [[self applicationDocumentsDirectory] path];
NSArray *docsDirectoryContents = [[NSFileManager defaultManager] contentsOfDirectoryAtPath:docsDirectoryPath error:nil];
for (NSString *docsDirectoryItem in docsDirectoryContents) {
    // Look at docsDirectoryItem. If it's something you want to keep, do nothing.
    // If it's something you don't recognize, remove it.
}

这种方法可能容易出错。你必须绝对确定你知道你想要保存的每一个文件，否则你可能会删除重要的数据。另一方面，您可以删除外部二进制文件，而不需要知道用于存储它们的文件/目录名称。

下面这个版本可以删除每个表中的每条记录。

斯威夫特4

static func resetDatabase() {
    do {
        try dataStore.persistentStoreCoordinator.managedObjectModel.entities.forEach { (entity) in
            if let name = entity.name {
                let fetch = NSFetchRequest<NSFetchRequestResult>(entityName: name)
                let request = NSBatchDeleteRequest(fetchRequest: fetch)
                try mainContext.execute(request)
            }
        }

        try mainContext.save()
    } catch {
        print("error resenting the database: \(error.localizedDescription)")
    }
}

假设你正在使用MagicalRecord并且有一个默认的持久性存储:

我不喜欢所有假设存在特定文件和/或要求输入实体名称或类的解决方案。这是一个Swift(2)，安全的方式删除所有实体的所有数据。删除后，它将重新创建一个新的堆栈(我实际上不确定这部分是多么必要)。

这是godo的“注销”风格的情况下，当你想删除一切，但有一个工作的存储和moc，以获得新的数据(一旦用户登录…)

extension NSManagedObject {

    class func dropAllData() {

        MagicalRecord.saveWithBlock({ context in

            for name in NSManagedObjectModel.MR_defaultManagedObjectModel().entitiesByName.keys {
                do { try self.deleteAll(name, context: context) }
                catch { print("⚠️ ✏️ Error when deleting \(name): \(error)") }
            }

            }) { done, err in
                MagicalRecord.cleanUp()
                MagicalRecord.setupCoreDataStackWithStoreNamed("myStoreName")
        }
    }

    private class func deleteAll(name: String, context ctx: NSManagedObjectContext) throws {
        let all = NSFetchRequest(entityName: name)
        all.includesPropertyValues = false

        let allObjs = try ctx.executeFetchRequest(all)
        for obj in allObjs {
            obj.MR_deleteEntityInContext(ctx)
        }

    }
}

iOS 10 + Swift 3解决方案:

func clearCoreDataStore() {
    let delegate = UIApplication.shared.delegate as! AppDelegate
    let context = delegate.persistentContainer.viewContext

    for i in 0...delegate.persistentContainer.managedObjectModel.entities.count-1 {
        let entity = delegate.persistentContainer.managedObjectModel.entities[i]

        do {
            let query = NSFetchRequest<NSFetchRequestResult>(entityName: entity.name!)
            let deleterequest = NSBatchDeleteRequest(fetchRequest: query)
            try context.execute(deleterequest)
            try context.save()

        } catch let error as NSError {
            print("Error: \(error.localizedDescription)")
            abort()
        }
    }
}

遍历所有核心数据实体并清除它们

我采取了Grouchal的代码，为了加快速度，我使用了并发模式的枚举(NSEnumerationConcurrent)，它比for循环快了一点(在我的应用程序中，我为测试人员添加了这个功能，以便他们可以清除数据和做测试用例，而不是删除和安装应用程序)

- (void)resetObjects
{
    [self deleteAllObjectsInEntity:@"Entity1"];
    [self deleteAllObjectsInEntity:@"Entity2"];
    [self deleteAllObjectsInEntity:@"Entity3"];
    [self deleteAllObjectsInEntity:@"Entity4"];
}

-(void) deleteAllObjectsInEntity:(NSString*) entityName
{
    MainDataContext *coreDataContext = [MainDataContext sharedInstance];
    NSManagedObjectContext *currentContext = coreDataContext.managedObjectContext;
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:entityName inManagedObjectContext:currentContext];
    [fetchRequest setEntity:entity];

    NSError *error;
    NSArray *items = [currentContext executeFetchRequest:fetchRequest error:&error];

    [items enumerateObjectsWithOptions:NSEnumerationConcurrent usingBlock:^(NSManagedObject * obj, NSUInteger idx, BOOL *stop) {
        [currentContext deleteObject:obj];
    }];


    if (![currentContext save:&error]) {
        NSLog(@"Error deleting %@ - error:%@",entityName,error);
    }
}

Swift 4/5, iOS 9+

重新构建整个CoreData SQLite文件将确保擦除所有数据，因此删除所有实体。只需调用deleteAndRebuild()。

class CoreDataStack {
    // Change this
    static let datamodelName = "ProjectName"
    static let storeType = "sqlite"

    static let persistentContainer = NSPersistentContainer(name: datamodelName)
    private static let url: URL = {
        let url = FileManager.default.urls(for: .applicationSupportDirectory, in: .userDomainMask)[0].appendingPathComponent("\(datamodelName).\(storeType)")

        assert(FileManager.default.fileExists(atPath: url.path))

        return url
    }()

    static func loadStores() {
        persistentContainer.loadPersistentStores(completionHandler: { (nsPersistentStoreDescription, error) in
            if let error = error {
                fatalError(error.localizedDescription)
            }
        })
    }

    static func deleteAndRebuild() {
        try! persistentContainer.persistentStoreCoordinator.destroyPersistentStore(at: url, ofType: storeType, options: nil)

        loadStores()
    }
}