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
延续戴夫·德隆的回答。
Swift版本，照顾iOS 9和以前的版本以及。我还介绍了错误处理:
let appDelegate： AppDelegate = UIApplication.sharedApplication（）.delegate as！应用委托
let fetchRequest = NSFetchRequest(entityName: "Car")
if #available(iOS 9.0, *) {
let delete = NSBatchDeleteRequest(fetchRequest: fetchRequest)
do {
try appDelegate.persistentStoreCoordinator.executeRequest(delete, withContext: appDelegate.managedObjectContext)
} catch let error as NSError {
print("Error occured while deleting: \(error)")
}
} else {
// Fallback on earlier versions
let carRequest = NSFetchRequest()
carRequest.entity = NSEntityDescription.entityForName("Cars", inManagedObjectContext: appDelegate.managedObjectContext)
carRequest.includesPropertyValues = false
do {
let cars: NSArray = try appDelegate.managedObjectContext.executeFetchRequest(carRequest)
for car in cars {
appDelegate.managedObjectContext.delete(car)
}
try appDelegate.managedObjectContext.save()
} catch let error as NSError {
print("Error occured while fetching or saving: \(error)")
}
}
其他回答
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)
}
func deleteAll(entityName: String) {
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: entityName)
let deleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
deleteRequest.resultType = .resultTypeObjectIDs
guard let context = self.container?.viewContext
else { print("error in deleteAll")
return }
do {
let result = try context.execute(deleteRequest) as? NSBatchDeleteResult
let objectIDArray = result?.result as? [NSManagedObjectID]
let changes: [AnyHashable : Any] = [NSDeletedObjectsKey : objectIDArray as Any]
NSManagedObjectContext.mergeChanges(fromRemoteContextSave: changes, into: [context])
} catch {
print(error.localizedDescription)
}
}
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];
}
iOS 10及以上版本
适用于所有版本。传递实体名称并遍历删除所有条目并保存上下文。
func deleteData(entityToFetch: String, completion: @escaping(_ returned: Bool) ->()) {
let context = NSManagedObjectContext()
context = your managedObjectContext
let fetchRequest = NSFetchRequest<NSFetchRequestResult>()
fetchRequest.entity = NSEntityDescription.entity(forEntityName: entityToFetch, in: context)
fetchRequest.includesPropertyValues = false
do {
let results = try context.fetch(fetchRequest) as! [NSManagedObject]
for result in results {
context.delete(result)
}
try context.save()
completion(true)
} catch {
completion(false)
print("fetch error -\(error.localizedDescription)")
}
}
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")
