I have a Playlist entity and Song entity. They have a one to many relationship where one playlist contains many songs. I want to remove the relationship and instead add a new attribute called playlistId of type UUID and assign the playlist Id to it during migration.

I have tried and check all the class names in the Mapping model file but the methods refuse to get called.

Is it because my core data stack is in a custom directory? At the moment in the mapping model, the custom class name is set to “MyAppName.MappingModel”

class DataController {
    static let shared = DataController()

    let container: NSPersistentContainer!
    
    init() {
        container = NSPersistentContainer(name: "Database")
        
        let coreDataDirectory = FileManager.getApplicationSupportDirectory().appendingPathComponent("Database")
        let description = NSPersistentStoreDescription(url: coreDataDirectory)
        
        self.container.persistentStoreDescriptions = [description]

        if let description = container.persistentStoreDescriptions.first {
            description.shouldMigrateStoreAutomatically = true
            description.shouldInferMappingModelAutomatically = false
        }

                                
        container.loadPersistentStores { [weak self] description, error in
            guard let self else { return }
            
            if let error = error {
                print("Core Data failed to load: (error.localizedDescription)")
                fatalError()
            }

            container.viewContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
        }
}

class MappingModel: NSEntityMigrationPolicy {
    override func createDestinationInstances(forSource sInstance: NSManagedObject, in mapping: NSEntityMapping, manager: NSMigrationManager) throws {
        //Never called.
        print("Running migration")
    }
}

extension Song {

    @nonobjc public class func fetchRequest() -> NSFetchRequest<Song> {
        return NSFetchRequest<Song>(entityName: "Song")
    }

    @NSManaged public var album: String?
    @NSManaged public var artist: String?
    @NSManaged public var artwork: String?
    @NSManaged public var fileExtension: String?
    @NSManaged public var name: String?
}