CoreData 版本控制和阻塞轻量级迁移

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【中文标题】CoreData 版本控制和阻塞轻量级迁移【英文标题】:CoreData versioning and blocking lightweight migration 【发布时间】:2012-03-06 17:35:03 【问题描述】:

我已经启用了我的核心数据模型的版本控制,并且一直在使用轻量级迁移。我的代码总是尝试进行轻量级迁移,然后如果由于模型不兼容而失败,它会退回到删除所有现有数据并从服务器重新获取。 所以轻量级迁移只是为了提高效率,而不是为了正确性。

我现在要做的是对我的模型进行更改,理论上轻量级迁移可以处理,但实际上我需要来自服务器的新数据。我想以某种方式标记模型,并且不能通过轻量级迁移进行升级。例如,如果字段名称未更改,但该字段的含义已更改,导致旧代码与新代码库不兼容。 (这只是一个例子。)

有没有人找到一种方法将两个模型标记为不兼容,以便轻量级迁移不会升级它们?

【问题讨论】:

【参考方案1】:

我以前也遇到过同样的问题。

我有一个方法会尝试使用映射模型迁移数据,如果您要关闭轻量级迁移,您应该使用该方法。

如果您不打算进行大量花哨的数据映射,xcode 将自动创建一个映射模型,该模型的工作方式与轻量级迁移完全相同。每次向 Core Data 添加新版本时,您所要做的就是创建一个新的“映射模型”文件。只需转到“文件 -> 新建 -> 新文件”,在核心数据下应该有一个映射模型模板。选择它并选择源和目标版本。

我没有在 github 上公开我的代码,所以我将在这里发布迁移方法。

- (BOOL)progressivelyMigrateURL:(NSURL*)sourceStoreURL ofType:(NSString*)type toModel:(NSManagedObjectModel*)finalModel

    NSError *error = nil;

    // if store dosen't exist skip migration
    NSString *documentDir = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];
    if(![NSBundle pathForResource:@"YongoPal" ofType:@"sqlite" inDirectory:documentDir])
    
        migrationProgress = 1.0;
        [self performSelectorOnMainThread:@selector(updateMigrationProgress) withObject:nil waitUntilDone:YES];

        // remove migration view
        [self.migrationView performSelectorOnMainThread:@selector(setHidden:) withObject:[NSNumber numberWithBool:YES] waitUntilDone:YES];
        [self.migrationView performSelectorOnMainThread:@selector(removeFromSuperview) withObject:nil waitUntilDone:YES];

        self.migrationView = nil;
        self.migrationProgressLabel = nil;
        self.migrationProgressView = nil;
        self.migrationSpinner = nil;

        return YES;
    

    //START:progressivelyMigrateURLHappyCheck
    NSDictionary *sourceMetadata = [NSPersistentStoreCoordinator metadataForPersistentStoreOfType:type URL:sourceStoreURL error:&error];

    if (!sourceMetadata)
    
        return NO;
    

    if ([finalModel isConfiguration:nil compatibleWithStoreMetadata:sourceMetadata])
    
        migrationProgress = 1.0;
        [self performSelectorOnMainThread:@selector(updateMigrationProgress) withObject:nil waitUntilDone:YES];

        // remove migration view
        [self.migrationView performSelectorOnMainThread:@selector(setHidden:) withObject:[NSNumber numberWithBool:YES] waitUntilDone:YES];
        [self.migrationView performSelectorOnMainThread:@selector(removeFromSuperview) withObject:nil waitUntilDone:YES];

        self.migrationView = nil;
        self.migrationProgressLabel = nil;
        self.migrationProgressView = nil;
        self.migrationSpinner = nil;

        error = nil;
        return YES;
    
    else
    
        migrationProgress = 0.0;
        [self.migrationView performSelectorOnMainThread:@selector(setHidden:) withObject:NO waitUntilDone:YES];
        [self performSelectorOnMainThread:@selector(updateMigrationProgress) withObject:nil waitUntilDone:YES];        
    
    //END:progressivelyMigrateURLHappyCheck

    //START:progressivelyMigrateURLFindModels
    //Find the source model
    NSManagedObjectModel *sourceModel = [NSManagedObjectModel mergedModelFromBundles:nil forStoreMetadata:sourceMetadata];
    if(sourceModel == nil)
    
        NSLog(@"%@", [NSString stringWithFormat:@"Failed to find source model\n%@", [sourceMetadata description]]);
        return NO;
    

    //Find all of the mom and momd files in the Resources directory
    NSMutableArray *modelPaths = [NSMutableArray array];
    NSArray *momdArray = [[NSBundle mainBundle] pathsForResourcesOfType:@"momd" inDirectory:nil];
    for (NSString *momdPath in momdArray)
    
        NSAutoreleasePool *pool = [NSAutoreleasePool new];
        NSString *resourceSubpath = [momdPath lastPathComponent];
        NSArray *array = [[NSBundle mainBundle] pathsForResourcesOfType:@"mom" inDirectory:resourceSubpath];
        [modelPaths addObjectsFromArray:array];
        [pool drain];
    

    NSArray* otherModels = [[NSBundle mainBundle] pathsForResourcesOfType:@"mom" inDirectory:nil];
    [modelPaths addObjectsFromArray:otherModels];

    if (!modelPaths || ![modelPaths count])
    
        //Throw an error if there are no models
        NSMutableDictionary *dict = [NSMutableDictionary dictionary];
        [dict setValue:@"No models found in bundle" forKey:NSLocalizedDescriptionKey];

        //Populate the error
        error = [NSError errorWithDomain:@"com.yongopal.coredata" code:500 userInfo:dict];
        if([[self.prefs valueForKey:@"debugMode"] isEqualToString:@"Y"])
        
            NSLog(@"error: %@", error);
        
        return NO;
    
    //END:progressivelyMigrateURLFindModels

    //See if we can find a matching destination model
    //START:progressivelyMigrateURLFindMap
    NSMappingModel *mappingModel = nil;
    NSManagedObjectModel *targetModel = nil;
    NSString *modelPath = nil;

    for(modelPath in modelPaths)
    
        targetModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:[NSURL fileURLWithPath:modelPath]];
        mappingModel = [NSMappingModel mappingModelFromBundles:nil forSourceModel:sourceModel destinationModel:targetModel];

        //If we found a mapping model then proceed
        if(mappingModel)
        
            break;
        
        else
        
            //Release the target model and keep looking
            [targetModel release];
            targetModel = nil;
        
    

    //We have tested every model, if nil here we failed
    if (!mappingModel)
    
        NSMutableDictionary *dict = [NSMutableDictionary dictionary];
        [dict setValue:@"No mapping models found in bundle" forKey:NSLocalizedDescriptionKey];
        error = [NSError errorWithDomain:@"com.yongopal.coredata" code:500 userInfo:dict];
        if([[self.prefs valueForKey:@"debugMode"] isEqualToString:@"Y"])
        
            NSLog(@"error: %@", error);
        
        return NO;
    
    //END:progressivelyMigrateURLFindMap

    //We have a mapping model and a destination model.  Time to migrate
    //START:progressivelyMigrateURLMigrate
    NSMigrationManager *manager = [[NSMigrationManager alloc] initWithSourceModel:sourceModel destinationModel:targetModel];

    // reg KVO for migration progress
    [manager addObserver:self forKeyPath:@"migrationProgress" options:NSKeyValueObservingOptionNew context:NULL];

    NSString *modelName = [[modelPath lastPathComponent] stringByDeletingPathExtension];
    NSString *storeExtension = [[sourceStoreURL path] pathExtension];
    NSString *storePath = [[sourceStoreURL path] stringByDeletingPathExtension];

    //Build a path to write the new store
    storePath = [NSString stringWithFormat:@"%@.%@.%@", storePath, modelName, storeExtension];
    NSURL *destinationStoreURL = [NSURL fileURLWithPath:storePath];

    if (![manager migrateStoreFromURL:sourceStoreURL type:type options:nil withMappingModel:mappingModel toDestinationURL:destinationStoreURL destinationType:type destinationOptions:nil error:&error])
    
        if([[self.prefs valueForKey:@"debugMode"] isEqualToString:@"Y"])
        
            NSLog(@"error: %@", error);
        
        [targetModel release];
        [manager removeObserver:self forKeyPath:@"migrationProgress"];
        [manager release];
        return NO;
    
    [targetModel release];
    [manager removeObserver:self forKeyPath:@"migrationProgress"];
    [manager release];
    //END:progressivelyMigrateURLMigrate

    //Migration was successful, move the files around to preserve the source
    //START:progressivelyMigrateURLMoveAndRecurse
    NSString *guid = [[NSProcessInfo processInfo] globallyUniqueString];
    guid = [guid stringByAppendingPathExtension:modelName];
    guid = [guid stringByAppendingPathExtension:storeExtension];
    NSString *appSupportPath = [storePath stringByDeletingLastPathComponent];
    NSString *backupPath = [appSupportPath stringByAppendingPathComponent:guid];

    NSFileManager *fileManager = [NSFileManager defaultManager];
    if (![fileManager moveItemAtPath:[sourceStoreURL path] toPath:backupPath error:&error])
    
        if([[self.prefs valueForKey:@"debugMode"] isEqualToString:@"Y"])
        
            NSLog(@"error: %@", error);
        
        //Failed to copy the file
        return NO;
    

    //Move the destination to the source path
    if (![fileManager moveItemAtPath:storePath toPath:[sourceStoreURL path] error:&error])
    
        if([[self.prefs valueForKey:@"debugMode"] isEqualToString:@"Y"])
        
            NSLog(@"error: %@", error);
        
        //Try to back out the source move first, no point in checking it for errors
        [fileManager moveItemAtPath:backupPath toPath:[sourceStoreURL path] error:nil];
        return NO;
    

    //We may not be at the "current" model yet, so recurse
    return [self progressivelyMigrateURL:sourceStoreURL ofType:type toModel:finalModel];
    //END:progressivelyMigrateURLMoveAndRecurse

这是我从一些我不记得标题的 Core Data 书籍中获得的方法的编辑版本。我希望我能把功劳归功于作者。 :S

请注意,我这里有一些代码,你应该在你的实现中删除它们。这主要是我用来更新迁移进度视图的东西。

你可以像这样使用这个方法:

NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"YongoPal.sqlite"];

// perform core data migrations if necessary
if(![self progressivelyMigrateURL:storeURL ofType:NSSQLiteStoreType toModel:self.managedObjectModel])

    // reset the persistent store on fail
    NSString *documentDir = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];
    NSError *error = nil;
    [[NSFileManager defaultManager] removeItemAtPath:[NSBundle pathForResource:@"YongoPal" ofType:@"sqlite" inDirectory:documentDir] error:&error];

else

    NSLog(@"migration succeeded!");

记得在使用之前删除轻量级迁移选项。

【讨论】:

我不知道这段代码如何解决我的问题。重申一下,我需要一种方式来说明两种模型不兼容。在 XCode 中创建映射模型文件后,我应该对它做些什么吗? 创建映射模型后,尝试从 Xcode(4.x) 中查看它,它应该会拉出实体映射和属性映射列表。从属性映射列表中,您应该看到目标和值表达式。只需删除要从迁移中排除的属性的值表达式(应类似于 $source.attribute_name),使其为空。当您运行我的progresslyMigrateURL:ofType:toModel: 方法时,它将迁移除具有空值表达式的属性之外的所有内容。 该方法来自 Marcus S. Zarra 的“Core Data: Apples API for persisting Data on Mac OSX”。我认为它现在称为“核心数据:ios、OS X 和 iCloud 的数据存储和管理”..【参考方案2】:

Apple 的Core Data Model Versioning and Data Migration Programming Guide 解决了如果“您有两个版本的模型,Core Data 通常将其视为等效的模型,而您希望被识别为不同的模型”,我认为这就是您要问的。

答案是在新模型中的一个实体或属性上设置 versionHashModifier。

在您的示例中,您将在含义已更改的字段上执行此操作。

【讨论】:

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