我有一种方法可以逐步迁移core data sqlite商店，但是存储多个NSManagedObjectModel版本，直到商店处于当前版本。该方法的灵感来自Marcus Zarra的核心数据手册中的代码。
该应用程序已投入生产，但我的方法在约0.5％的情况下失败。当它失败时返回NO并使用Crashlytics记录错误：
NSSQLiteErrorDomain = 14; NSUnderlyingException = "I/O error for database at <store url>. SQLite error code:14, 'unable to open database file'"
sqlite商店使用预写日志记录（WAL）如果我在首次手动删除{+metadataForPersistentStoreOfType:URL:error:后调用sqlite-WAL，我有时会遇到同样的错误{1}}档案。
- (BOOL)progressivelyMigrateURL:(NSURL*)sourceStoreURL
toModel:(NSManagedObjectModel*)finalModel
error:(NSError**)error
{
NSURL *storeDirectoryURL = [sourceStoreURL URLByDeletingLastPathComponent];
NSString *storeExtension = [sourceStoreURL pathExtension];
NSDictionary *sourceMetadata = [NSPersistentStoreCoordinator
metadataForPersistentStoreOfType:NSSQLiteStoreType
URL:sourceStoreURL
error:error];
if (!sourceMetadata) return NO;
while (![finalModel isConfiguration:nil
compatibleWithStoreMetadata:sourceMetadata]) {
NSManagedObjectModel *sourceModel =
[self managedObjectModelForMetadata:sourceMetadata];
if (!sourceModel) return NO;
NSString *modelName = nil;
NSManagedObjectModel *targetModel =
[self suitableTargetModelForMigrationFromSourceModel:sourceModel
modelName:&modelName];
if (!targetModel) return NO;
NSMigrationManager *manager =
[[NSMigrationManager alloc] initWithSourceModel:sourceModel
destinationModel:targetModel];
NSMappingModel *mappingModel =
[NSMappingModel mappingModelFromBundles:nil
forSourceModel:sourceModel
destinationModel:targetModel];
NSURL *destinationStoreURL =
[[storeDirectoryURL URLByAppendingPathComponent:modelName]
URLByAppendingPathExtension:storeExtension];
BOOL migrated = [manager migrateStoreFromURL:sourceStoreURL
type:NSSQLiteStoreType
options:nil
withMappingModel:mappingModel
toDestinationURL:destinationStoreURL
destinationType:NSSQLiteStoreType
destinationOptions:nil
error:error];
if (!migrated) return NO;
NSString *sourceModelName =
[self versionStringForManagedObjectModel:sourceModel];
NSURL *backUpURL = [self backupURLWithDirectoryURL:storeDirectoryURL
pathExtension:storeExtension
modelName:sourceModelName];
BOOL replaced = [self replaceStoreAtURL:sourceStoreURL
withStoreAtURL:destinationStoreURL
backupURL:backUpURL
error:error];
if (replaced == NO) return NO;
sourceMetadata = [NSPersistentStoreCoordinator
metadataForPersistentStoreOfType:NSSQLiteStoreType
URL:sourceStoreURL
error:error];
if (!sourceMetadata) return NO;
}
return YES;
}
- (NSManagedObjectModel *)managedObjectModelForMetadata:(NSDictionary *)metadata
{
for (NSURL *URL in [self modelURLs]) {
NSManagedObjectModel *model =
[[NSManagedObjectModel alloc] initWithContentsOfURL:URL];
if ([model isConfiguration:nil compatibleWithStoreMetadata:metadata]) {
return model;
}
}
return nil;
}
- (NSManagedObjectModel *)suitableTargetModelForMigrationFromSourceModel:(NSManagedObjectModel *)sourceModel
modelName:(NSString **)modelName
{
for (NSURL *modelURL in [self modelURLs]) {
NSManagedObjectModel *targetModel =
[[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
NSMappingModel *mappingModel =
[NSMappingModel mappingModelFromBundles:nil
forSourceModel:sourceModel
destinationModel:targetModel];
if (mappingModel) {
*modelName = [[modelURL lastPathComponent] stringByDeletingPathExtension];
return targetModel;
}
}
return nil;
}
- (NSArray *)modelURLs
{
NSMutableArray *modelURLs =
[[[NSBundle mainBundle] URLsForResourcesWithExtension:@"mom"
subdirectory:nil] mutableCopy];
NSArray *momdURLs =
[[[NSBundle mainBundle] URLsForResourcesWithExtension:@"momd"
subdirectory:nil] mutableCopy];
for (NSURL *momdURL in momdURLs) {
NSString *directory = [momdURL lastPathComponent];
NSArray *array =
[[NSBundle mainBundle] URLsForResourcesWithExtension:@"mom"
subdirectory:directory];
[modelURLs addObjectsFromArray:array];
}
return [modelURLs copy];
}
- (NSURL *)backupURLWithDirectoryURL:(NSURL *)URL
pathExtension:(NSString *)extension
modelName:(NSString *)name
{
NSString *GUID = [[NSProcessInfo processInfo] globallyUniqueString];
NSString *pathComponant = [NSString stringWithFormat:@"%@-%@", GUID, name];
return [[URL URLByAppendingPathComponent:pathComponant]
URLByAppendingPathExtension:extension];
}
- (BOOL)replaceStoreAtURL:(NSURL *)originalStoreURL
withStoreAtURL:(NSURL *)newStoreURL
backupURL:(NSURL *)backupURL
error:(NSError **)error
{
BOOL storeMoved = [self moveStoreAtURL:originalStoreURL
toURL:backupURL
error:error];
if (!storeMoved) return NO;
storeMoved = [self moveStoreAtURL:newStoreURL
toURL:originalStoreURL
error:error];
if (!storeMoved) return NO;
return YES;
}
- (BOOL)moveStoreAtURL:(NSURL *)sourceURL
toURL:(NSURL *)targetURL
error:(NSError **)error
{
NSMutableArray *sourceURLs = [@[sourceURL] mutableCopy];
NSMutableArray *targetURLs = [@[targetURL] mutableCopy];
NSString *walExtension = @"sqlite-wal";
if ([self storeAtURL:sourceURL hasAccessoryFileWithExtension:walExtension]) {
[sourceURLs addObject:[self URLByReplacingExtensionOfURL:sourceURL
withExtension:walExtension]];
[targetURLs addObject:[self URLByReplacingExtensionOfURL:targetURL
withExtension:walExtension]];
}
NSString *shmExtension = @"sqlite-shm";
if ([self storeAtURL:sourceURL hasAccessoryFileWithExtension:shmExtension]) {
[sourceURLs addObject:[self URLByReplacingExtensionOfURL:sourceURL
withExtension:shmExtension]];
[targetURLs addObject:[self URLByReplacingExtensionOfURL:targetURL
withExtension:shmExtension]];
}
NSFileManager *fileManager = [NSFileManager defaultManager];
for (int i = 0; i < [sourceURLs count]; i++) {
BOOL fileMoved = [fileManager moveItemAtURL:sourceURLs[i]
toURL:targetURLs[i]
error:error];
if (!fileMoved) return NO;
}
return YES;
}
- (BOOL)storeAtURL:(NSURL *)URL hasAccessoryFileWithExtension:(NSString *)extension
{
NSURL *accessoryURL = [self URLByReplacingExtensionOfURL:URL
withExtension:extension];
return [[NSFileManager defaultManager] fileExistsAtPath:[accessoryURL path]];
}
- (NSURL *)URLByReplacingExtensionOfURL:(NSURL *)URL withExtension:(NSString *)extension
{
return [[URL URLByDeletingPathExtension] URLByAppendingPathExtension:extension];
}
- (NSString *)versionStringForManagedObjectModel:(NSManagedObjectModel *)model
{
NSString *string = @"";
for (NSString *identifier in model.versionIdentifiers) {
string = [string stringByAppendingString:identifier];
}
return string;
}
抱歉超长代码。
答案 0 :(得分：3)
可能的原因是您的moveStoreAtURL:toURL:error:方法。您获得的错误是mentioned in Apple's docs，因为无法复制所有持久性存储的文件。看起来你正试图点击所有这些，但是（a）复制代码中有一个我现在无法找到的错误或（b）商店在你的应用程序中“活着”，正在使用持久存储协调器，因此您无法从副本获得一致的状态。
您可以通过一些调试来修复它，如果您确保该商店未被使用。更改日志模式会更好，也可能更可靠，因此您没有wal和shm文件（该链接也描述了这些文件）。更好的是，如果您的商店文件不是太大，请使用migratePersistentStore:toURL:options:withType:error让Core Data制作副本。这应该可以保证工作，但在某些情况下它可能会占用太多内存。
答案 1 :(得分：2)
我使用NSMigrationManager，因此我无法使用NSPersistentStoreCoordinator＆＃39; s - migratePersistentStore...，所以我的解决方案是强制执行检查点操作：
- (void)performCheckpointStoreWithSourceModel:(NSManagedObjectModel *)sourceModel sourceStoreURL:(NSURL *)sourceStoreURL {
NSPersistentStoreCoordinator *tempPSC = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:sourceModel];
[tempPSC addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:sourceStoreURL options:@{NSSQLitePragmasOption: @{@"journal_mode": @"DELETE"}} error:nil];
[tempPSC removePersistentStore:[tempPSC persistentStoreForURL:sourceStoreURL] error:nil];
}
...在使用NSMigrationManager执行迁移之前：
if (![manager migrateStoreFromURL:sourceStoreURL
type:type
options:nil
withMappingModel:mappingModel
toDestinationURL:destinationStoreURL
destinationType:type
destinationOptions:nil
error:error]) {
return NO;
}