我已启用核心数据模型的版本控制，并一直在使用轻量级迁移。我的代码始终尝试进行轻量级迁移，然后如果由于模型不兼容而失败，则将其归结为删除所有现有数据并从服务器进行重新提取。
因此，轻量级迁移仅用于提高效率，而对于正确性则不是必需的。
我现在想做的是更改我的模型，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，并且无法通过轻量级迁移进行升级。例如，如果字段名称没有更改，但是该字段的含义已更改，以致旧代码与新代码库不兼容。 （这只是一个例子。）
有没有人找到将两个模型标记为不兼容的方法，以便轻量级迁移不会升级它们？
最佳答案
我以前也遇到过同样的问题。
我有一种方法将尝试使用“映射模型”迁移数据，如果要关闭轻量级迁移，则应使用该方法。
如果您不打算进行大量精美的数据映射，则xcode将自动创建一个映射模型，该模型的工作原理与轻量级迁移完全相同。您要做的就是每次向Core Data添加新版本时都创建一个新的“映射模型”文件。只需转到“文件->新建->新文件”，然后在“核心数据”下应该有一个映射模型模板。选择它，然后选择源版本和目标版本。
我没有在github上公开提供我的代码，因此我将在此处发布迁移方法。
- (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其标题的Core Data书中获得的方法的编辑版本。我希望我能称赞作者。 ：S
当心，这里有一些代码，您应该在实现中删除它们。我主要用于更新有关迁移进度的视图。
您可以这样使用此方法：
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!");
}
使用此方法之前，请记住先删除轻量级迁移选项。
关于iphone - CoreData版本控制和阻止轻量级迁移，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/9588906/