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 3中重置实体:
func resetAllRecords(in entity : String) // entity = Your_Entity_Name
{
let context = ( UIApplication.shared.delegate as! AppDelegate ).persistentContainer.viewContext
let deleteFetch = NSFetchRequest<NSFetchRequestResult>(entityName: entity)
let deleteRequest = NSBatchDeleteRequest(fetchRequest: deleteFetch)
do
{
try context.execute(deleteRequest)
try context.save()
}
catch
{
print ("There was an error")
}
}
其他回答
为什么不将接收到的数据与现有缓存一起折叠呢?否则它就不是真正的“刷新”，而是“重新开始”，你也可以删除SQLLite文件并重新开始(假设你没有持久化其他数据)。
对于Swift 2.0:
class func clearCoreData(entity:String) {
let fetchRequest = NSFetchRequest()
fetchRequest.entity = NSEntityDescription.entityForName(entity, inManagedObjectContext: moc!)
fetchRequest.includesPropertyValues = false
do {
if let results = try moc!.executeFetchRequest(fetchRequest) as? [NSManagedObject] {
for result in results {
moc!.deleteObject(result)
}
try moc!.save()
}
} catch {
LOG.debug("failed to clear core data")
}
}
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)")
}
}
Dave Delongs的Swift 2.0回答让我崩溃了(在iOS 9中)
但这个方法奏效了:
let fetchRequest = NSFetchRequest(entityName: "Car")
let deleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
do {
try managedObjectContext.executeRequest(deleteRequest)
try managedObjectContext.save()
}
catch let error as NSError {
// Handle error
}
在Swift 3中重置实体:
func resetAllRecords(in entity : String) // entity = Your_Entity_Name
{
let context = ( UIApplication.shared.delegate as! AppDelegate ).persistentContainer.viewContext
let deleteFetch = NSFetchRequest<NSFetchRequestResult>(entityName: entity)
let deleteRequest = NSBatchDeleteRequest(fetchRequest: deleteFetch)
do
{
try context.execute(deleteRequest)
try context.save()
}
catch
{
print ("There was an error")
}
}
