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
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 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")
}
}
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)
}
}
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")
iOS 11.3和Swift 4.1
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: entityName)
let batchDeleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest )
batchDeleteRequest.resultType = .resultTypeCount
do {
let batchDeleteResult = try dataController.viewContext.execute(batchDeleteRequest) as! NSBatchDeleteResult
print("The batch delete request has deleted \(batchDeleteResult.result!) records.")
dataController.viewContext.reset() // reset managed object context (need it for working)
} catch {
let updateError = error as NSError
print("\(updateError), \(updateError.userInfo)")
}
你必须在执行之后调用重置。如果不是，它将不会在表视图上更新。
