ios - 在 NSBatchDeleteRequest 之后使用核心数据

Question

在我的应用程序中，当我从网络服务刷新实体的内容时，我删除了核心数据中的所有记录并插入了所有新记录。但是，很多时候记录并没有从上下文中删除，即使我再次调用上下文也是如此。因此，当我保存时，旧的仍然存在，而我最终只是堆叠在现有的之上，得到很多重复项。我怎样才能完全清除上下文，这样我就不必担心重复？

    var appDelegate = UIApplication.shared.delegate as! AppDelegate
    var context = appDelegate.persistentContainer.viewContext
    let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "V_ServiceDetails")

    // Clear all
    let request = NSBatchDeleteRequest(fetchRequest: fetchRequest)

    do {
        let result = try context.execute(request)
    } catch {}

    appDelegate = UIApplication.shared.delegate as! AppDelegate
    context = appDelegate.persistentContainer.viewContext

    // Add new ones
    for svc in self.svcs {
        let result = NSEntityDescription.insertNewObject(forEntityName: "V_ServiceDetails", into: context)

        result.setValue(svc.Car_VIN, forKey: "car_VIN")
        result.setValue(svc.Cust_Veh_ID, forKey: "cust_Veh_ID")

        do { try context.save() } catch {}
    }

Answer 1

试试下面这个函数:

func deleteAll() {

    // Managed Object Context
    let managedObjectContext = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext

    // Save the changes of the Managed Object Context before executing the Batch Delete Request
    if managedObjectContext.hasChanges {
        do {
            try managedObjectContext.save()
        } catch {
            // Error
        }
    }

    // Craete a Fetch Request
    let fetchRequest: NSFetchRequest<ManagedObject> = ManagedObject.fetchRequest()

    // Initiliaze the Batch Delete Request
    let batchDeleteRequest = NSBatchDeleteRequest.init(fetchRequest: fetchRequest as! NSFetchRequest<NSFetchRequestResult>)

    // Configure the Batch Delete Request
    batchDeleteRequest.resultType = .resultTypeCount

    do {

        // Execute the Batch Delete Request
        try managedObjectContext.execute(batchDeleteRequest)

        // Reset the Managed Object Context
        managedObjectContext.reset()

        // try self.fetchedResultsController.performFetch()
        // If you have a Table View? Use this function
        // self.tableView.reloadData()

    } catch {
        // Error
    }
}