NSManagedObjectから任意のモデルに相互にマップしあう定義をプロトコル化するとCoreData Wrapper書くのに捗りそう

Mappable.swift

import Foundation
import CoreData

protocol NSManagedObjectMappable: NSManagedObject where MapFrom.MapFrom == Self {
    associatedtype MapFrom: MappableFromNSManagedObject
    static func mappedObject(from object: MapFrom, in context: NSManagedObjectContext) -> Self
}

enum MappingError: Error {
    case missingNonOptionalValue(String)
}

protocol MappableFromNSManagedObject where MapFrom.MapFrom == Self {
    associatedtype MapFrom: NSManagedObjectMappable
    static func mappedObject(from object: MapFrom) throws -> Self
}

extension MappableFromNSManagedObject {
    static func mapValue<T>(from object: MapFrom, keyPath: KeyPath<MapFrom, T?>) throws -> T {
        guard let value = object[keyPath: keyPath] else {
            throw MappingError.missingNonOptionalValue(String(describing: keyPath))
        }
        return value
    }
}

struct Sample {
    let string: String
    let number: Int
    let date: Date
}

extension Sample: MappableFromNSManagedObject {
    static func mappedObject(from object: SampleRecord) throws -> Sample {
        return Sample(
            string: try mapValue(from: object, keyPath: \.string),
            number: Int(object.number),
            date: try mapValue(from: object, keyPath: \.date)
        )
    }
}

extension SampleRecord: NSManagedObjectMappable {
    static func mappedObject(from object: Sample, in context: NSManagedObjectContext) -> Self {
        let entity = Self.init(context: context)
        entity.string = object.string
        entity.number = Int32(object.number)
        entity.date = object.date
        return entity
    }
}

class StoreService {
    private let coreDataStack: CoreDataStack

    init(from coreDataStack: CoreDataStack) {
        self.coreDataStack = coreDataStack
    }

    func insert<T: MappableFromNSManagedObject>(_ object: T) throws {
        let context = coreDataStack.newBackgroundContext
        let entity = T.MapFrom.mappedObject(from: object, in: context)
        try context.save()
    }
}