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
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)")
}
}
其他回答
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)")
}
}
NSBatchDeleteRequest Swift 5.5和Xcode 13.2
删除SQLite持久存储中的对象，而不加载到内存中。在持久存储上执行的更改不会反映在当前内存中的对象中。
执行批量删除之后，从持久存储中删除内存中的所有对象。
下面是执行batchDeleteRequest的一些方便的扩展方法
extension NSManagedObject {
private static var entityName: String {
return String(describing: self)
}
static func fetchRequest<Self>(
with predicate: NSPredicate? = nil,
configureBlock: ((NSFetchRequest<Self>) -> Void)? = nil
) -> NSFetchRequest<Self> where Self: NSFetchRequestResult {
let request = NSFetchRequest<Self>(entityName: entityName)
request.predicate = predicate
configureBlock?(request)
return request
}
static func batchDelete(with fetchRequest: NSFetchRequest<NSFetchRequestResult>,
in context: NSManagedObjectContext) {
let batchDeteleRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
batchDeteleRequest.resultType = .resultTypeObjectIDs
do {
if let fetchResult = try context.execute(batchDeteleRequest) as? NSBatchDeleteResult,
let deletedManagedObjectIds = fetchResult.result as? [NSManagedObjectID], !deletedManagedObjectIds.isEmpty {
let changes = [NSDeletedObjectsKey: deletedManagedObjectIds]
NSManagedObjectContext.mergeChanges(fromRemoteContextSave: changes, into: [context])
}
} catch {
print("Error while executing batchDeleteRequest: \(error.localizedDescription)")
}
}
}
示例:我们可以通过传递fetchRequest调用batchDelete静态方法批量删除实体
class Entity: NSManagedObject {
@NSManaged var name: String?
@NSManaged var value: String?
}
extension Entity {
static func executeBatchDelete(in context: NSManagedObjectContext) {
let predicate = NSPredicate(format: "\(#keyPath(Entity.value)) == %@)", "abc")
let deleteRequest: NSFetchRequest<NSFetchRequestResult> = Entity.fetchRequest(with: predicate)
Entity.batchDelete(with: deleteRequest, in: context)
}
}
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")
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)")
}
}
}
Swift 4, iOS 10+ 静态函数，可以应用于任何实体删除其所有数据
protocol NSManagedObjectHelper {
}
extension NSManagedObject: NSManagedObjectHelper {
}
extension NSManagedObjectHelper where Self: NSManagedObject {
static func removeAllObjectsInContext(_ managedContext: NSManagedObjectContext) {
let request: NSFetchRequest = NSFetchRequest(entityName: String(describing: self))
let deleteRequest = NSBatchDeleteRequest(fetchRequest: request)
do {
deleteRequest.resultType = .resultTypeObjectIDs//to clear objects from memory
let result = try managedContext.execute(deleteRequest) as? NSBatchDeleteResult
if let objectIDArray = result?.result as? [NSManagedObjectID] {
let changes = [NSDeletedObjectsKey : objectIDArray]
/*By calling mergeChangesFromRemoteContextSave, all of the NSManagedObjectContext instances that are referenced will be notified that the list of entities referenced with the NSManagedObjectID array have been deleted and that the objects in memory are stale. This causes the referenced NSManagedObjectContext instances to remove any objects in memory that are loaded which match the NSManagedObjectID instances in the array.*/
NSManagedObjectContext.mergeChanges(fromRemoteContextSave: changes, into: [managedContext])
}
try managedContext.save()
} catch let error {
print(error)
}
}
}
“房间”是一个实体
Room.removeAllObjectsInContext(self.persistentContainer.viewContext)
在20191025编辑:如果我们在同一个项目中使用多个目标，"Self.fetchRequest()"指令可能会导致问题。所以替换为NSFetchRequest(entityName: String(description: self))
