Custom NSMigrationPolicy methods not invoked when NSMappingModel is created in code

Hi, I’m running into an issue with Core Data migrations using a custom NSMappingModel created entirely in Swift (not using .xcmappingmodel files).

Setup: • I’m performing a migration with a manually constructed NSMappingModel • One of the NSEntityMapping instances is configured as follows: • mappingType = .customEntityMappingType (or .transformEntityMappingType) • entityMigrationPolicyClassName is set to a valid subclass of NSEntityMigrationPolicy • The class implements the expected methods like: @objc func createDestinationInstances(…) throws { … } @objc func createCustomDestinationInstance(…) throws -> NSManagedObject { … }

The policy class is instantiated (confirmed via logging in init()), but none of the migration methods are ever called.

I have also tried adding valid NSPropertyMapping instances with real valueExpression bindings to force activation, but that didn’t make a difference.

Constraints: • I cannot use .xcmappingmodel files in this context due to transformable attributes not compatible with the visual editor. • Therefore, I need the entire mapping model to be defined in Swift.

Workaround:

As a temporary workaround, I’m migrating the data manually using two persistent stores and NSManagedObjectContext, but I’d prefer to rely on NSMigrationManager as designed.

Question:

Is there a known limitation that prevents Core Data from invoking NSMigrationPolicy methods when using in-memory NSMappingModel instances? Or is there any specific setup required to trigger them when not loading from .xcmappingmodel?

Thanks in advance.