我使用Core Data在本地持久化Web服务调用的结果。web服务返回完整的对象模型,比如说,“Cars”——可能有2000辆车(我不能让web服务返回小于1辆或ALL辆的任何东西。

下次打开应用程序时,我希望通过再次调用所有汽车的Web服务来刷新Core Data持久化副本,但是为了防止重复,我需要首先清除本地缓存中的所有数据。

是否有一种更快的方法来清除管理对象上下文中特定实体的所有实例(例如,类型为“CAR”的所有实体),或者我需要查询它们调用,然后遍历结果删除每个,然后保存?

理想情况下,我可以说删除实体所在的所有地方等等。


当前回答

OOP方式,没有任何字符串作为实体名称 Swift 3+, Xcode 10+

func batchDelete<T>(in context: NSManagedObjectContext, fetchRequest: NSFetchRequest<T>) throws {
    guard let request = fetchRequest as? NSFetchRequest<NSFetchRequestResult> else {
        throw ErrorService.defaultError
    }
    let batchDeleteRequest = NSBatchDeleteRequest(fetchRequest: request)
    do {
        try context.execute(batchDeleteRequest)
    } catch {
        throw error
    }
}

然后调用do/catch块

    let fetchRequest: NSFetchRequest<YourEntity> = YourEntity.fetchRequest()
    do {
        let data = try context.fetch(fetchRequest)
        if data.count > 0 {
            try self.batchDelete(in: context, fetchRequest: fetchRequest)
        }
    } catch {
        // throw error
    }

其他回答

如果实体包含很多条目,最好的方法是这样,因为它节省内存

 - (void)deleteAll:(NSManagedObjectContext *)managedObjectContext entityName:(NSString *)entityName
{
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    [managedObjectContext setUndoManager:nil];
    NSEntityDescription *entity = [NSEntityDescription entityForName:entityName inManagedObjectContext:managedObjectContext];
    [fetchRequest setEntity:entity];
    [fetchRequest setIncludesPropertyValues:NO];
    [fetchRequest setFetchLimit:100]; // you can change this number if you want
    NSError *error;
    NSArray *items = [managedObjectContext executeFetchRequest:fetchRequest error:&error];
    while ([items count] > 0) {
        @autoreleasepool {
            for (NSManagedObject *item in items) {
                [managedObjectContext deleteObject:item];
            }
            if (![managedObjectContext save:&error]) {
                NSLog(@"Error deleting %@ - error:%@",self.entityName, error);
            }
        }
        items = [managedObjectContext executeFetchRequest:fetchRequest error:&error];
    }
}

iOS 9.0及以上版本:

NSBatchDeleteRequest用于删除核心数据中的记录。它的工作速度非常快,从一个实体删除所有记录所需的时间更少。它需要NSFetchRequest作为参数。如果你想从一个实体删除所有记录,你可以使用它,它为我工作。

let manageObject:NSManagedObjectContext = appDelegateObject.managedObjectContext

let fetchRequest = NSFetchRequest(entityName: “EnityName”)

let deleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)

let persistCor:NSPersistentStoreCoordinator = appDelegateObject.persistentObject
 do {
        try persistCor.executeRequest(deleteRequest, withContext: manageObject)
        try manageObject.save()
    } catch {
        print(error?.localizedDescription)
    }

快速清除DB中的所有对象:

func purgeAllData() {
    let uniqueNames = persistentContainer.managedObjectModel.entities.compactMap({ $0.name })

    uniqueNames.forEach { (name) in
      let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: name)
       let batchDeleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
         do {
        try persistentContainer.viewContext.execute(batchDeleteRequest)
      } catch {
        let nserror = error as NSError
        fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
      }
   }
 }

一个很好的答案已经贴出来了,这只是一个推荐!

一个好方法是添加一个类别到NSManagedObject和实现一个方法,就像我做的:

头文件(例如NSManagedObject+Ext.h)

@interface NSManagedObject (Logic)

+ (void) deleteAllFromEntity:(NSString*) entityName;

@end

代码文件:(例如NSManagedObject+Ext.m)

@implementation NSManagedObject (Logic)

+ (void) deleteAllFromEntity:(NSString *)entityName {
    NSManagedObjectContext *managedObjectContext = [AppDelegate managedObjectContext];
    NSFetchRequest * allRecords = [[NSFetchRequest alloc] init];
    [allRecords setEntity:[NSEntityDescription entityForName:entityName inManagedObjectContext:managedObjectContext]];
    [allRecords setIncludesPropertyValues:NO];
    NSError * error = nil;
    NSArray * result = [managedObjectContext executeFetchRequest:allRecords error:&error];
    for (NSManagedObject * profile in result) {
        [managedObjectContext deleteObject:profile];
    }
    NSError *saveError = nil;
    [managedObjectContext save:&saveError];
}

@end

... 你唯一要做的就是从应用程序委托获取managedObjectContext,或者你在哪里都有它;)

之后你可以这样使用它:

[NSManagedObject deleteAllFromEntity:@"EntityName"];

进一步的优化可以是删除entityname的参数,而从clazzname获取名称。这将导致使用:

[ClazzName deleteAllFromEntity];

一个更干净的impl(作为NSManagedObjectContext的类别):

@implementation NSManagedObjectContext (Logic)

- (void) deleteAllFromEntity:(NSString *)entityName {
    NSFetchRequest * allRecords = [[NSFetchRequest alloc] init];
    [allRecords setEntity:[NSEntityDescription entityForName:entityName inManagedObjectContext:self]];
    [allRecords setIncludesPropertyValues:NO];
    NSError * error = nil;
    NSArray * result = [self executeFetchRequest:allRecords error:&error];
    for (NSManagedObject * profile in result) {
        [self deleteObject:profile];
    }
    NSError *saveError = nil;
    [self save:&saveError];
}

@end

那时的用法:

[managedObjectContext deleteAllFromEntity:@"EntityName"];

在Swift 2.0中:

func deleteAllData(entity: String)
{
    let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
    let managedContext = appDelegate.managedObjectContext
    let fetchRequest = NSFetchRequest(entityName: entity)
    fetchRequest.returnsObjectsAsFaults = false

    do 
    {
        let results = try managedContext.executeFetchRequest(fetchRequest)
        for managedObject in results
        {
            let managedObjectData:NSManagedObject = managedObject as! NSManagedObject
            managedContext.deleteObject(managedObjectData)
        }
    } catch let error as NSError {
        print("Detele all data in \(entity) error : \(error) \(error.userInfo)")
    }
}