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

迅捷用户界面

从实体中获取实例,然后循环删除每个实例。

@Environment(\.managedObjectContext) var moc
    
@FetchRequest(sortDescriptors: []) var wizards: FetchedResults<Wizard>

var body: some View {
    VStack {
        List() { }

        Button("Delete all") {
            for wizard in wizards {
                moc.delete(wizard)
            }
            
            if moc.hasChanges {
                try? moc.save()
            }
        }
    }
}

其他回答

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")
        }
    }

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)")
    }
}

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。

Swift 3解决方案与iOS 9 'NSBatchDeleteRequest'和回退到早期的iOS版本,作为'NSManagedObjectContext'的扩展实现。苹果参考https://developer.apple.com/library/content/featuredarticles/CoreData_Batch_Guide/BatchDeletes/BatchDeletes.html

extension NSManagedObjectContext {
    func batchDeleteEntities<T: NSManagedObject>(ofType type: T.Type) throws {
        let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: String(describing: type.self))
        if #available(iOS 9.0, *) {
            let request = NSBatchDeleteRequest(fetchRequest: fetchRequest)
            let result = try execute(request) as? NSBatchDeleteResult
            if let objectIDArray = result?.result as? [NSManagedObjectID] {
                let changes = [NSDeletedObjectsKey: objectIDArray]
                NSManagedObjectContext.mergeChanges(fromRemoteContextSave: changes, into: [self])
            }
        } else {
            fetchRequest.includesPropertyValues = false
            let results = try fetch(fetchRequest)
            if let actualResults = results as? [NSManagedObject], !actualResults.isEmpty {
                actualResults.forEach { delete($0) }
            }
        }
    }
}

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)")
    }
}