FetchingData.swift

final class CoreDataStore: NSPersistentContainer {   
    func fetchedResultsController(named name: String, sortDescriptors: [NSSortDescriptor], predicate: NSPredicate? = nil, sectionNameKeyPath: String? = nil) -> NSFetchedResultsController<NSFetchRequestResult> {
        let request = NSFetchRequest<NSFetchRequestResult>(entityName: name)
        if let predicate = predicate {
            request.predicate = predicate
        }
        request.sortDescriptors = sortDescriptors.isEmpty ? nil : sortDescriptors
        return NSFetchedResultsController(fetchRequest: request, managedObjectContext: viewContext, sectionNameKeyPath: sectionNameKeyPath, cacheName: nil)
    }
}

final class PlanetManager {
    lazy var planetsController: NSFetchedResultsController<Planet> = {
        let descriptors = [NSSortDescriptor(key: "position", ascending: true)]
        return dataStore.fetchedResultsController(named: "Planet", sortDescriptors: descriptors) as! NSFetchedResultsController<Planet>
    }()
}