在尝试构建本地 Core Data 备份方法时，我遵循了 Tom Harrington 的解决方案 使用他的示例代码。
我已经到了可以恢复备份的地步。 但是，一旦我在恢复备份后尝试修改或添加新对象，应用程序就会崩溃：
线程 1：“对象 0xb8e4b835591334a8 x-coredata://AFC6072C-23E5-49E2-880E-662F57BDA847/Item/p9 持久 无法从此 NSManagedObjectContext 的协调器访问商店”
我假设我在恢复后仍然连接到旧的 Store Coordinator，但我不知道如何避免这种情况。
我基于 Apple 的默认 Core Data 蓝图应用程序创建了一个示例。 您可以在这里下载完整的源代码。
这是基本包含逻辑的持久性控制器和备份视图模型。
class BackupViewModel: ObservableObject {
@Published var backups: [String]
@Published var restoreMode: Bool = false
@Published var selectedURL: URL?
@Published var viewID: UUID = UUID()
init(){
backups = UserDefaults.standard.array(forKey: "backupsKey") as? [String] ?? []
}
func addBackup() {
let url = newBackupURL()
selectedURL = url
backups = [url.description]
UserDefaults.standard.set(backups, forKey: "backupsKey")
do{
try PersistenceController.shared.container.copyPersistentStores(to: url)
} catch {
}
}
func newBackupURL() -> URL {
let exportPath = NSTemporaryDirectory() + "Backup\(Date().description).sqlite"
let exportURL = URL(fileURLWithPath: exportPath)
return exportURL
}
}
持久化控制器
import CoreData
struct PersistenceController {
static let shared = PersistenceController()
let container: NSPersistentContainer
init(inMemory: Bool = false) {
container = NSPersistentContainer(name: "CoreDataBackup")
if inMemory {
container.persistentStoreDescriptions.first!.url = URL(fileURLWithPath: "/dev/null")
}
container.loadPersistentStores(completionHandler: { (storeDescription, error) in
if let error = error as NSError? {
fatalError("Unresolved error \(error), \(error.userInfo)")
}
})
container.viewContext.automaticallyMergesChangesFromParent = true
}
func resoredInit(){
container.persistentStoreDescriptions.first!.url = URL(fileURLWithPath: "/dev/null")
container.loadPersistentStores(completionHandler: { (storeDescription, error) in
if let error = error as NSError? {
fatalError("Unresolved error \(error), \(error.userInfo)")
}
})
container.viewContext.automaticallyMergesChangesFromParent = true
}
}
extension NSPersistentContainer {
enum CopyPersistentStoreErrors: Error {
case invalidDestination(String)
case destinationError(String)
case destinationNotRemoved(String)
case copyStoreError(String)
case invalidSource(String)
}
/// Restore backup persistent stores located in the directory referenced by `backupURL`.
///
/// **Be very careful with this**. To restore a persistent store, the current persistent store must be removed from the container. When that happens, **all currently loaded Core Data objects** will become invalid. Using them after restoring will cause your app to crash. When calling this method you **must** ensure that you do not continue to use any previously fetched managed objects or existing fetched results controllers. **If this method does not throw, that does not mean your app is safe.** You need to take extra steps to prevent crashes. The details vary depending on the nature of your app.
/// - Parameter backupURL: A file URL containing backup copies of all currently loaded persistent stores.
/// - Throws: `CopyPersistentStoreError` in various situations.
/// - Returns: Nothing. If no errors are thrown, the restore is complete.
func restorePersistentStore(from backupURL: URL) throws -> Void {
guard backupURL.isFileURL else {
throw CopyPersistentStoreErrors.invalidSource("Backup URL must be a file URL")
}
var isDirectory: ObjCBool = false
if FileManager.default.fileExists(atPath: backupURL.path, isDirectory: &isDirectory) {
if !isDirectory.boolValue {
throw CopyPersistentStoreErrors.invalidSource("Source URL must be a directory")
}
} else {
throw CopyPersistentStoreErrors.invalidSource("Source URL must exist")
}
for persistentStore in persistentStoreCoordinator.persistentStores {
guard let loadedStoreURL = persistentStore.url else {
continue
}
let backupStoreURL = backupURL.appendingPathComponent(loadedStoreURL.lastPathComponent)
guard FileManager.default.fileExists(atPath: backupStoreURL.path) else {
throw CopyPersistentStoreErrors.invalidSource("Missing backup store for \(backupStoreURL)")
}
do {
// Remove the existing persistent store first
try persistentStoreCoordinator.remove(persistentStore)
} catch {
print("Error removing store: \(error)")
throw CopyPersistentStoreErrors.copyStoreError("Could not remove persistent store before restore")
}
do {
// Clear out the existing persistent store so that we'll have a clean slate for restoring.
try persistentStoreCoordinator.destroyPersistentStore(at: loadedStoreURL, ofType: persistentStore.type, options: persistentStore.options)
// Add the backup store at its current location
let backupStore = try persistentStoreCoordinator.addPersistentStore(ofType: persistentStore.type, configurationName: persistentStore.configurationName, at: backupStoreURL, options: persistentStore.options)
// Migrate the backup store to the non-backup location. This leaves the backup copy in place in case it's needed in the future, but backupStore won't be useful anymore.
let restoredTemporaryStore = try persistentStoreCoordinator.migratePersistentStore(backupStore, to: loadedStoreURL, options: persistentStore.options, withType: persistentStore.type)
print("Restored temp store: \(restoredTemporaryStore)")
} catch {
throw CopyPersistentStoreErrors.copyStoreError("Could not restore: \(error.localizedDescription)")
}
}
}
/// Copy all loaded persistent stores to a new directory. Each currently loaded file-based persistent store will be copied (including journal files, external binary storage, and anything else Core Data needs) into the destination directory to a persistent store with the same name and type as the existing store. In-memory stores, if any, are skipped.
/// - Parameters:
/// - destinationURL: Destination for new persistent store files. Must be a file URL. If `overwriting` is `false` and `destinationURL` exists, it must be a directory.
/// - overwriting: If `true`, any existing copies of the persistent store will be replaced or updated. If `false`, existing copies will not be changed or remoted. When this is `false`, the destination persistent store file must not already exist.
/// - Throws: `CopyPersistentStoreError`
/// - Returns: Nothing. If no errors are thrown, all loaded persistent stores will be copied to the destination directory.
func copyPersistentStores(to destinationURL: URL, overwriting: Bool = false) throws -> Void {
guard destinationURL.isFileURL else {
throw CopyPersistentStoreErrors.invalidDestination("Destination URL must be a file URL")
}
// If the destination exists and we aren't overwriting it, then it must be a directory. (If we are overwriting, we'll remove it anyway, so it doesn't matter whether it's a directory).
var isDirectory: ObjCBool = false
if !overwriting && FileManager.default.fileExists(atPath: destinationURL.path, isDirectory: &isDirectory) {
if !isDirectory.boolValue {
throw CopyPersistentStoreErrors.invalidDestination("Destination URL must be a directory")
}
// Don't check if destination stores exist in the destination dir, that comes later on a per-store basis.
}
// If we're overwriting, remove the destination.
if overwriting && FileManager.default.fileExists(atPath: destinationURL.path) {
do {
try FileManager.default.removeItem(at: destinationURL)
} catch {
throw CopyPersistentStoreErrors.destinationNotRemoved("Can't overwrite destination at \(destinationURL)")
}
}
// Create the destination directory
do {
try FileManager.default.createDirectory(at: destinationURL, withIntermediateDirectories: true, attributes: nil)
} catch {
throw CopyPersistentStoreErrors.destinationError("Could not create destination directory at \(destinationURL)")
}
for persistentStoreDescription in persistentStoreDescriptions {
guard let storeURL = persistentStoreDescription.url else {
continue
}
guard persistentStoreDescription.type != NSInMemoryStoreType else {
continue
}
let temporaryPSC = NSPersistentStoreCoordinator(managedObjectModel: persistentStoreCoordinator.managedObjectModel)
let destinationStoreURL = destinationURL.appendingPathComponent(storeURL.lastPathComponent)
if !overwriting && FileManager.default.fileExists(atPath: destinationStoreURL.path) {
// If the destination exists, the migratePersistentStore call will update it in place. That's fine unless we're not overwriting.
throw CopyPersistentStoreErrors.destinationError("Destination already exists at \(destinationStoreURL)")
}
do {
let newStore = try temporaryPSC.addPersistentStore(ofType: persistentStoreDescription.type, configurationName: persistentStoreDescription.configuration, at: persistentStoreDescription.url, options: persistentStoreDescription.options)
let _ = try temporaryPSC.migratePersistentStore(newStore, to: destinationStoreURL, options: persistentStoreDescription.options, withType: persistentStoreDescription.type)
} catch {
throw CopyPersistentStoreErrors.copyStoreError("\(error.localizedDescription)")
}
}
}
}
我最近在我的 SwiftUI 项目中遇到了这个问题。当我尝试更新 viewContext 时，它仍然不起作用。你修好了吗？