nicol3a

/// An object that wants to be convertible in a managed object should implement the `ObjectConvertible` protocol.
protocol ObjectConvertible {
    /// An identifier that is used to fetch the corresponding database object.
    var identifier: String? { get }
}

nicol3a

class Event: ObjectConvertible {
    var title: String?
    var date: Date?
    private(set) var identifier: String?

    init(title: String, date: Date?, identifier: String? = nil) {
        self.title = title
        self.date = date
        self.identifier = identifier
    }

nicol3a

/// A `NSManagedObject` that wants to be converted from an `ObjectConvertible` object should implement the `ManagedObjectConvertible` protocol.
protocol ManagedObjectConvertible {
    /// An object which should implement the `ObjectConvertible` protocol.
    associatedtype T

    /// A String representing a URI that provides an archiveable reference to the object in Core Data.
    var identifier: String? { get }

    /// Insert an object in Core Data.
    ///

nicol3a

extension ManagedObjectConvertible where T: ObjectConvertible, Self: NSManagedObject {
    var identifier: String? {
        return objectID.uriRepresentation().absoluteString
    }

    static func insert(_ object: T, with context: NSManagedObjectContext) {
        guard object.identifier == nil else { return }

        let managedObject = Self(context: context)
        managedObject.from(object: object)

nicol3a

@objc(EventManagedObject)
public class EventManagedObject: NSManagedObject, ManagedObjectConvertible {
    typealias T = Event

    func from(object: Event) {
        title = object.title
        date = object.date
    }

    func toObject() -> Event {

nicol3a

// Get context
let context: NSManagedObjectContext = ...

// Create
let eventToInsert = Event(title: "I went to the hairdresser", date: Date())
EventManagedObject.insert(object: eventToInsert, with: context)

// Read
let events: [Event] = EventManagedObject.fetchAll(from: context)

nicol3a

@objc(EventManagedObject)
public class EventManagedObject: NSManagedObject, ManagedObjectConvertible {
    static func fetchAll(from context: NSManagedObjectContext) -> [Event] {
        let request = NSFetchRequest<EventManagedObject>(entityName: "EventManagedObject")
        request.returnsObjectsAsFaults = false

        do {
            let eventManagedObjects = try context.fetch(request)
            let events = eventManagedObjects.map { $0.toObject() }

nicol3a

class EventStore {
    private let context: NSManagedObjectContext

    init(context: NSManagedObjectContext) {
        self.context = context
    }

    func insert(_ event: Event) {
        EventManagedObject.insert(event, with: context)
    }

nicol3a

class AppDelegate: UIResponder, UIApplicationDelegate {
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Initialize store
        let context: NSManagedObjectContext = ...
        let store = EventStore(context: context)

        // Initialize root view controller
        let viewController = EventListTableViewController(store: store)

        // Initialize window...