ManagedObjectConvertible.swift

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)

        try? context.save()
    }

    static func update(_ object: T, with context: NSManagedObjectContext) {
        guard let managedObject = get(object: object, with: context) else {
            return
        }

        managedObject.from(object: object)

        try? context.save()
    }

    static func delete(_ object: T, with context: NSManagedObjectContext) {
        guard let managedObject = get(object: object, with: context) else {
            return
        }

        context.delete(managedObject)

        try? context.save()
    }

    static func fetchAll(from context: NSManagedObjectContext) -> [T] {
        let request = NSFetchRequest<Self>(entityName: String(describing: self))
        request.returnsObjectsAsFaults = false

        do {
            let managedObjects = try context.fetch(request)
            return managedObjects.map { $0.toObject() }
        } catch {
            return [T]()
        }
    }

    private static func get(object: T, with context: NSManagedObjectContext) -> Self? {
        guard
            let identifier = object.identifier,
            let uri = URL(string: identifier),
            let objectID = context.persistentStoreCoordinator?.managedObjectID(forURIRepresentation: uri) else
        {
            return nil
        }

        do {
            return try context.existingObject(with: objectID) as? Self
        } catch {
            return nil
        }
    }
}