Core Data migration problem: “Persistent store migration failed, missing source managed object model.”

Question

The Background

• A Cocoa Non Document Core Data project with two Managed Object Models.
• Model 1 stays the same. Model 2 has changed, s

Answer 1

Rather than merging all models in the bundle, I've specified the two models I want to use (model 1 and the new version of model 2) and merged them using modelByMergingModels:

This doesn't seem right. Why merge the models? You want to use model 2, migrating your store from model 1.

From the NSManagedObjectModel class reference

modelByMergingModels:

Creates a single model from an array of existing models.

You don't need to do anything special/specific with your source model (model 1).. just so long as it's in your bundle, the automatic lightweight migration process will discover and use it.

I would suggest abandoning the mapping model you created in Xcode, as I've seen terrible performance in comparison with the automatic-lightweight migrations. Your mileage may vary, my changes between models are different to yours, but i wouldn't be surprised. Try some timing with and without your own mapping model in the bundle.

 /* Inferred mapping */
 NSError *error;
 NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                          [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption,
                          [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption,nil];
 NSPersistentStore *migratedStore = [persistentStoreCoordinator addPersistentStoreWithType:nil
                                                                             configuration:nil
                                                                                       URL:self.storeURL
                                                                                   options:options
                                                                                     error:&error];
 migrationWasSuccessful = (migratedStore != nil);

You can verify in your code that your source model is available, by attempting to load it and verify that it is not nil:

NSString *modelDirectoryPath = [[NSBundle mainBundle] pathForResource:@"YourModelName" ofType:@"momd"];
if (modelDirectoryPath == nil) return nil;
NSString *modelPath = [modelDirectoryPath stringByAppendingPathComponent:@"YourModelName"];
NSURL *modelFileURL = [NSURL fileURLWithPath:modelPath];
NSManagedObjectModel *modelOne = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelFileURL];
if (modelOne == nil) {
    NSLog(@"Woops, Xcode lost my source model");
}
else {
    [modelOne release];
}

This assumes in your project you have a resource "YourModelName.xcdatamodeld" and "YourModelName.xcdatamodel" within it.

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Also, you can check if that model is compatible with your existing, pre-migration persistent store:

NSError *error;
NSDictionary *storeMeta = [NSPersistentStoreCoordinator metadataForPersistentStoreOfType:nil URL:self.storeURL error:&error];
if (storeMeta == nil) {
    // Unable to read store meta
    return NO;
}
BOOL isCompatible = [modelOne isConfiguration:nil compatibleWithStoreMetadata:storeMeta];

That code assumes you have a method -storeURL to specify where the persistent store is loaded from.