CoreDataAsKeyValueStore.swift

import Foundation
import CoreData

class PersistentContainer: NSPersistentContainer {
    static let modelName = "MyDataModel"
    static var main: PersistentContainer? = {
        guard
            let modelURL = Bundle.framework.url(forResource: modelName, withExtension: "momd"),
            let model = NSManagedObjectModel(contentsOf: modelURL)
        else {
            return  nil
        }

        let container = PersistentContainer(name: modelName, managedObjectModel: model)
        container.loadPersistentStores { (_, error) in
            print(error as Any)
        }
        return container
    }()
}

struct CoreDataStorage {
    var container: Entity? // this is Swift's auto-generated class for the entity you modeled in your DataCoreModel
    let context = PersistentContainer.main!.viewContext
    let decoder = JSONDecoder()
    let encoder = JSONEncoder()

    init?() {
        let request = Entity.fetchRequest()
        let results = try? context.fetch(request)
        if results?.count == 0 {
            container = Entity(context: context)
        } else {
            container = results?.first ?? Entity(context: context)
        }
    }

    func integer(forKey defaultName: String) -> Int {
        (container?.value(forKey: defaultName) as? Int) ?? 0
    }

    func string(forKey defaultName: String) -> String? {
        container?.value(forKey: defaultName) as? String
    }

    func object<T>(ofType type: T.Type, forKey defaultName: String) -> T? where T : Decodable {
        guard let data = container?.value(forKey: defaultName) as? Data else {
            return nil
        }
        return try? decoder.decode(T.self, from: data)
    }

    func set(_ value: Any?, forKey defaultName: String) {
        container?.setValue(value, forKey: defaultName)
        try? context.save()
    }

    func setObject<T>(_ value: T, forKey defaultName: String) where T : Encodable {
        container?.setValue(try? encoder.encode(value), forKey: defaultName)
        try? context.save()
    }

    func setValuesForKeys(_ keyedValues: [String : Any]) {
        keyedValues.forEach {
            self.set($0.value, forKey: $0.key)
        }
        try? context.save()
    }

    func removeObject(forKey defaultName: String) {
        container?.setValue(nil, forKey: defaultName)
    }

    func removeObjects(forKeys keys: [String]) {
        keys.forEach {
            removeObject(forKey: $0)
        }
    }

    func dictionaryRepresentation() -> [String : Any] {
        guard let container = container else { return [:] }
        return container.dictionaryWithValues(
            forKeys: Mirror(reflecting: container).children.compactMap { $0.label }
        )
    }
}

struct CoreDataStore {
    var storage: Storage
    var name: String
    var otherAttribute: DecodableClass

    var name: String? {
        get {
            storage.string(forKey: "name")
        }
        set {
            storage.setObject(newValue, forKey: "name")
        }
    }
  
    var otherAttribute: String? {
        get {
            storage.string(forKey: "otherAttribute")
        }
        set {
            storage.set(newValue, forKey: "otherAttribute")
        }
    }


    func clear() {
        storage.removeObjects(forKeys: ["name", "otherAttribute"])
    }

    init(storage: CoreDataStorage) {
        self.storage = storage
    }
}