UIManagedDocument migrate data model

问题:

I am working on an iPhone app that uses a subclass of UIManagedDocument and stores its documents on iCloud.

It was all working fine until I changed my core data model / scheme (adding a new model version - like I had several times in the past few weeks). I added a new property and changed the data type of one of the existing properties.

Now when I run my app I don't seem to be able to load my documents with UIManagedDocument's -openWithCompletionHandler:. I can create new documents and read/write those. If I change the data model version back 1 then I am able to read the existing docs, but not the new ones.

From what I understand I am only do lightweight migrations to the data model and UIManagedDocument is supposed to handle that right?

Any advice would be greatly appreciated!

回答1:

In a subclass of UIManagedDocument you may want to try overriding managedObjectModel like so:

- (NSManagedObjectModel *)managedObjectModel
{
    NSString *path = [[NSBundle mainBundle] pathForResource:@"<ModelNameHere>" ofType:@"momd"];
    NSURL *momURL = [NSURL fileURLWithPath:path];
    NSManagedObjectModel *managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:momURL];

    return managedObjectModel;
}

回答2:

Given below is based on my understanding:

NOTE - I haven't tried it for iCloud but I have tested it for non-icloud and seems ok.

UIManagedDocument configures the managedObjectModel and a Persistent Store Coordinator by itself

When migration needs to be done, just set the UIManagedDocument's persistentStoreOptions

//Note - In this example, managedDocument is a UIManagedDocument property

self.managedDocument.persistentStoreOptions = [NSDictionary dictionaryWithObjectsAndKeys:
                                        [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption,
                                        [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];

Refer:

• Apple Documentation on Core Data Versioning
• Point of using NSPersistentStoreCoordinator?