iPhone CoreData Automatic Light Migration

This post is pieced together from these 3 sources:

• Apple doco
• iPhone Development: Core Data Migration Problems?
• What do I have to do to get Core Data to automatically migrate models?

So there’s basically 3 steps to do (BEFORE you change your xcdatamodel file):

1. Set the Persistent Store options for automatic migration:

Change your persistentStoreCoordinator creation to this (replace YOURDB):

[code]
– (NSPersistentStoreCoordinator *)persistentStoreCoordinator {

if (persistentStoreCoordinator != nil) {
return persistentStoreCoordinator;
}

NSURL *storeUrl = [NSURL fileURLWithPath: [[self applicationDocumentsDirectory] stringByAppendingPathComponent: @"YOURDB.sqlite"]];

// handle db upgrade
NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption,
[NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];

NSError *error = nil;
persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel: [self managedObjectModel]];
if (![persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeUrl options:options error:&error]) {
// Handle error
}

return persistentStoreCoordinator;
}

[/code]

2. Version your Data Model and Edit the new file

1. Select your xcdatamodel file
2. Design->Data Model->Add Model Version (expand your xcdatamodeld item)
3. Select the “2” (or later) file, Design->Data Model->Set Current Version (edit this version)

3. Specify the momd resource

Change your managedObjectModel implementation to this (replace YOURRESOURCENAME)…

[code]
– (NSManagedObjectModel *)managedObjectModel {

if (managedObjectModel != nil) {
return managedObjectModel;
}

NSString *path = [[NSBundle mainBundle] pathForResource:@"YOURRESOURCENAME" ofType:@"momd"];
NSURL *momURL = [NSURL fileURLWithPath:path];
managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:momURL];

return managedObjectModel;
}
[/code]

Build and run!