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
Swift 4, iOS 12和Xcode 10更新
100%工作，只是剪切和粘贴
只要把这个函数放在相关的类中，并在viewDidLoad()或任何地方或在一个函数或按钮下调用这个函数self.deleteData()，这样通过单击一个按钮，所有来自实体的数据都应该被删除，并替换“myEntity”作为你在核心数据中定义的实体
func deleteData() {
let appDel:AppDelegate = (UIApplication.shared.delegate as! AppDelegate)
let context:NSManagedObjectContext = appDel.persistentContainer.viewContext
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "myEntity")
fetchRequest.returnsObjectsAsFaults = false
do {
let results = try context.fetch(fetchRequest)
for managedObject in results {
if let managedObjectData: NSManagedObject = managedObject as? NSManagedObject {
context.delete(managedObjectData)
}
}
} catch let error as NSError {
print("Deleted all my data in myEntity error : \(error) \(error.userInfo)")
}
}
其他回答
Swift4+和Xcode 10+ 使用下面的代码删除实体中的所有记录。
func deleteAllRecords(entity : String) {
let managedContext = CoreDataManager.sharedManager.persistentContainer.viewContext //your context
let deleteFetch = NSFetchRequest<NSFetchRequestResult>(entityName: entity)
let deleteRequest = NSBatchDeleteRequest(fetchRequest: deleteFetch)
do {
try managedContext.execute(deleteRequest)
try managedContext.save()
} catch {
print ("There was an error")
}
}
如何使用
self.deleteEntityData(entity: "YOUR_ENTITY_NAME")
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
}
斯威夫特3。X和Swift 4。X，简单。只改变你的表格
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "YourTable")
fetchRequest.returnsObjectsAsFaults = false
do
{
let results = try context.fetch(fetchRequest)
for managedObject in results
{
let managedObjectData:NSManagedObject = managedObject as! NSManagedObject
context.delete(managedObjectData)
}
} catch let error as NSError {
print("Detele all my data in \(entity) error : \(error) \(error.userInfo)")
}
更干净和通用一点:添加这个方法:
- (void)deleteAllEntities:(NSString *)nameEntity
{
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:nameEntity];
[fetchRequest setIncludesPropertyValues:NO]; //only fetch the managedObjectID
NSError *error;
NSArray *fetchedObjects = [theContext executeFetchRequest:fetchRequest error:&error];
for (NSManagedObject *object in fetchedObjects)
{
[theContext deleteObject:object];
}
error = nil;
[theContext save:&error];
}
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)")
}
}
