Core Data 数据版本/迁移

{
    NSPersistenceFrameworkVersion = 641;
    NSStoreModelVersionHashes =     {
        IMPChatSession = <1d1f9997 5ad2eb64 ed28853b 255c3384 f4978d43 6b54119f bc37776f 9382a644>;
        IMPChatSetting = <8d414f3c c71afbf6 cf2e7a9e d42e548c 24dfe5ff 8fd299a9 c57881d6 70d2ba2f>;
        IMPRecent = <05593ecc 8e61b083 71b8f5a0 2c97d873 4db29dd6 5a63ffb8 968bf814 c7bf6304>;
    };
    NSStoreModelVersionHashesVersion = 3;
    NSStoreModelVersionIdentifiers =     (
        ""
    );
    NSStoreType = SQLite;
    NSStoreUUID = "1AAFEF41-289B-4F22-BBD7-E05796B3B651";
    "_NSAutoVacuumLevel" = 2;
}

NSError *error = nil;
NSURL *storeURL = <#The URL of a persistent store#>;
NSPersistentStoreCoordinator *psc = <#The coordinator#>;
NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
    [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption,
    [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];
 
BOOL success = [psc addPersistentStoreWithType:<#Store type#>
                    configuration:<#Configuration or nil#> URL:storeURL
                    options:options error:&error];
if (!success) {
    // Handle the error.
}

// 迁移入口
- (void)migrate:(NSError *__autoreleasing *)error {
    __block UIBackgroundTaskIdentifier bgTask;
    bgTask = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
        [[UIApplication sharedApplication] endBackgroundTask:bgTask];
        bgTask = UIBackgroundTaskInvalid;
    }];

    CoreDataMigrationManager *migrationManager = [CoreDataMigrationManager new];
    migrationManager.delegate = self;
    
    BOOL OK = [migrationManager progressivelyMigrateURL:[self sourceStoreURL]
                                                 ofType:[self sourceStoreType]
                                                toModel:[self managedObjectModel]
                                                  error:error];
    if (OK) {
        NSLog(@"migration complete");
    }

    [[UIApplication sharedApplication] endBackgroundTask:bgTask];
    bgTask = UIBackgroundTaskInvalid;
    return OK;
}

// CoreDataMigrationManager.m
- (BOOL)progressivelyMigrateURL:(NSURL *)sourceStoreURL
                         ofType:(NSString *)type
                        toModel:(NSManagedObjectModel *)finalModel
                          error:(NSError **)error
{
    NSDictionary *sourceMetadata = [NSPersistentStoreCoordinator metadataForPersistentStoreOfType:type
    URL:sourceStoreURL
    error:error];

    if (!sourceMetadata) {
        return NO;
    }
    // 1、检查数据与模型版本兼容性
    if ([finalModel isConfiguration:nil
        compatibleWithStoreMetadata:sourceMetadata]) {
        if (NULL != error) {
            *error = nil;
        }
        return YES;
    }

    // 2、查找数据版本v对应的模型版本v、下一模型版本v+1、映射模型mapping model
    NSManagedObjectModel *sourceModel = [self sourceModelForSourceMetadata:sourceMetadata];
    NSManagedObjectModel *destinationModel = nil;
    NSMappingModel *mappingModel = nil;
    NSString *modelName = nil;
    if (![self getDestinationModel:&destinationModel
                      mappingModel:&mappingModel
                         modelName:&modelName
                    forSourceModel:sourceModel
                             error:error]) {
        return NO;
    }

    // 3、指定的mapping model
    NSArray *mappingModels = @[mappingModel];
    if ([self.delegate respondsToSelector:@selector(migrationManager:mappingModelsForSourceModel:)]) {
        NSArray *explicitMappingModels = [self.delegate migrationManager:self mappingModelsForSourceModel:sourceModel];
        if (0 < explicitMappingModels.count) {
            mappingModels = explicitMappingModels;
        }
    }

    // 4、迁移
    NSURL *destinationStoreURL = [self destinationStoreURLWithSourceStoreURL:sourceStoreURL
                                                                   modelName:modelName];
    NSMigrationManager *manager = [[NSMigrationManager alloc] initWithSourceModel:sourceModel
                                                                 destinationModel:destinationModel];
    [manager addObserver:self
              forKeyPath:@"migrationProgress"
                 options:NSKeyValueObservingOptionNew
                 context:nil];
    BOOL didMigrate = NO;
    for (NSMappingModel *mappingModel in mappingModels) {
        didMigrate = [manager migrateStoreFromURL:sourceStoreURL
                                             type:type
                                          options:nil
                                 withMappingModel:mappingModel
                                 toDestinationURL:destinationStoreURL
                                  destinationType:type
                               destinationOptions:nil
                                            error:error];
    }
    [manager removeObserver:self
                 forKeyPath:@"migrationProgress"];
    if (!didMigrate) {
        return NO;
    }

    // 数据备份及继续递归迁移
    if (![self backupSourceStoreAtURL:sourceStoreURL
          movingDestinationStoreAtURL:destinationStoreURL
                                error:error]) {
        return NO;
    }

    return [self progressivelyMigrateURL:sourceStoreURL
                                  ofType:type
                                 toModel:finalModel
                                   error:error];
}

- (BOOL)createDestinationInstancesForSourceInstance:(NSManagedObject *)sourceInstance
                                      entityMapping:(NSEntityMapping *)mapping
                                            manager:(NSMigrationManager *)manager
                                              error:(NSError *__autoreleasing *)error
{
    NSNumber *modelVersion = [mapping.userInfo valueForKey:@"modelVersion"];
    if (modelVersion.integerValue == 2 || modelVersion.integerValue == 3) {

        NSMutableArray *sourceKeys = [sourceInstance.entity.attributesByName.allKeys mutableCopy];
        NSDictionary *sourceValues = [sourceInstance dictionaryWithValuesForKeys:sourceKeys];

        NSManagedObject *destinationInstance = [NSEntityDescription insertNewObjectForEntityForName:[mapping destinationEntityName]
                                                                             inManagedObjectContext:[manager destinationContext]];
        NSArray *destinationKeys = destinationInstance.entity.attributesByName.allKeys;

        for (NSString *key in destinationKeys) {
            id value = [sourceValues valueForKey:key];
            // Avoid NULL values
            if (value && ![value isEqual:[NSNull null]]) {
                [destinationInstance setValue:value forKey:key];
            }
        }

        if (modelVersion.integerValue == 2) {
            // Check if we've already created the authors lookup
            NSMutableDictionary *authorLookup = [manager lookupWithKey:@"authors"];
            // Check if we've already created this author
            NSString *authorName = [sourceInstance valueForKey:@"authorName"];
            NSManagedObject *author = [authorLookup valueForKey:authorName];
            if (!author) {
                // Create the author
                author = [NSEntityDescription insertNewObjectForEntityForName:@"Author"
                                                       inManagedObjectContext:[manager destinationContext]];

                [author setValue:authorName forKey:@"name"];

                // Populate lookup for reuse
                [authorLookup setValue:author forKey:authorName];
            }
            [destinationInstance performSelector:@selector(addAuthorsObject:) withObject:author];
        } else if (modelVersion.integerValue == 3) {
            NSArray *sourceUsers = [sourceInstance valueForKey:@"users"];
            for (NSManagedObject *sourceUser in sourceUsers) {

                NSManagedObject *file = [NSEntityDescription insertNewObjectForEntityForName:@"File"
                                                                      inManagedObjectContext:manager.destinationContext];
                [file setValue:[sourceInstance valueForKey:@"fileURL"] forKey:@"fileURL"];
                [file setValue:destinationInstance forKey:@"book"];
                
                NSInteger userId = [[sourceUser valueForKey:@"userId"] integerValue];
                NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"User"];
                request.predicate = [NSPredicate predicateWithFormat:@"userId = %d", userId];
                NSManagedObject *destinationUser = [[manager.destinationContext executeFetchRequest:request error:nil] lastObject];
                [file setValue:destinationUser forKey:@"user"];
            }
        }

        /// 告知迁移管理器，建立关联
        [manager associateSourceInstance:sourceInstance
                 withDestinationInstance:destinationInstance
                        forEntityMapping:mapping];

        return YES;
    } else {
        return [super createDestinationInstancesForSourceInstance:sourceInstance
                                                    entityMapping:mapping
                                                          manager:manager
                                                            error:error];
    }
}