'Failed to call designated initializer on NSManagedObject class' NSManagedObject and NSCoding - swift

Question

I'm attempting to:
Load an array of custom objects from JSON file.
Save it in CoreData.
Fetch it using NSFetchRequest.
Note: Each element in the array of custom objects named 'Cube' also contains a nested array of custom objects named 'Algorithm', which also conform to NSCoding (shown in code snippet below).
Steps 1 + 2 seem to work fine. The error occurs when fetching the top level Entities named 'Cube', specifically right after the self.init() is called inside the nested class 'Algorithm'.
Algorithm class:
#objc(Algorithm)
public class Algorithm: NSManagedObject, Decodable, Encodable, NSSecureCoding {
enum CodingKeys: String, CodingKey {
case imageNumber, alg, alternativeAlgs, type, tags, isFavorite, optimalMoves, name }
public static var supportsSecureCoding = true
public func encode(with coder: NSCoder) {
coder.encode(imageNumber, forKey: CodingKeys.imageNumber.rawValue)
coder.encode(optimalMoves, forKey: CodingKeys.optimalMoves.rawValue)
coder.encode(alg, forKey: CodingKeys.alg.rawValue)
coder.encode(name, forKey: CodingKeys.name.rawValue)
coder.encode(type, forKey: CodingKeys.type.rawValue)
coder.encode(isFavorite, forKey: CodingKeys.isFavorite.rawValue)
coder.encode(alternativeAlgs, forKey: CodingKeys.alternativeAlgs.rawValue)
coder.encode(tags, forKey: CodingKeys.tags.rawValue) }
required convenience public init?(coder: NSCoder) {
self.init()
imageNumber = coder.decodeObject(forKey: CodingKeys.imageNumber.rawValue) as? String ?? ""
optimalMoves = coder.decodeObject(forKey: CodingKeys.optimalMoves.rawValue) as? String ?? ""
alg = coder.decodeObject(forKey: CodingKeys.alg.rawValue) as? String ?? ""
name = coder.decodeObject(forKey: CodingKeys.name.rawValue) as? String ?? ""
type = coder.decodeObject(forKey: CodingKeys.type.rawValue) as? String ?? ""
isFavorite = coder.decodeBool(forKey: CodingKeys.isFavorite.rawValue)
alternativeAlgs = coder.decodeObject(forKey: CodingKeys.alternativeAlgs.rawValue) as? [String] ?? []
tags = coder.decodeObject(forKey: CodingKeys.tags.rawValue) as? [String] ?? [] }
required convenience public init(from decoder: Decoder) throws {
guard let context = decoder.userInfo[CodingUserInfoKey.managedObjectContext] as? NSManagedObjectContext else {
throw DecoderConfigurationError.missingManagedObjectContext
}
self.init(context: context)
let container = try decoder.container(keyedBy: CodingKeys.self)
self.imageNumber = try container.decode(String.self, forKey: .imageNumber)
self.optimalMoves = try container.decode(String.self, forKey: .optimalMoves)
self.alg = try container.decode(String.self, forKey: .alg)
self.name = try container.decode(String.self, forKey: .name)
self.type = try container.decode(String.self, forKey: .type)
self.isFavorite = try container.decode(Bool.self, forKey: .isFavorite)
self.alternativeAlgs = try container.decode([String].self, forKey: .alternativeAlgs) as [String]
self.tags = try container.decode([String].self, forKey: .tags) as [String] }
public func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: CodingKeys.self)
try container.encode(imageNumber, forKey: .imageNumber)
try container.encode(optimalMoves, forKey: .optimalMoves)
try container.encode(alg, forKey: .alg)
try container.encode(name, forKey: .name)
try container.encode(type, forKey: .type)
try container.encode(isFavorite, forKey: .isFavorite)
try container.encode(alternativeAlgs, forKey: .alternativeAlgs)
try container.encode(tags, forKey: .tags) }
}
extension Algorithm {
#nonobjc public class func fetchRequest() -> NSFetchRequest<Algorithm> {
return NSFetchRequest<Algorithm>(entityName: "Algorithm")
}
#NSManaged public var alg: String
#NSManaged public var alternativeAlgs: [String]
#NSManaged public var imageNumber: String
#NSManaged public var isFavorite: Bool
#NSManaged public var name: String
#NSManaged public var optimalMoves: String
#NSManaged public var tags: [String]
#NSManaged public var type: String
#NSManaged public var cube: Cube?
}
extension Algorithm : Identifiable {
}
After reading people's comments I am aware I should replace the self.init() with NSManagedObject's designated init, but I haven't found the right way to do so. The app crashes after replacing the self.init() with the following code:
let context = CoreDataManager.shared.container.viewContext
self.init(context: context)
// self.init()
FWI - in the CoreData.xcdatamodeled file inspector the algorithms array is defined as Transformable with a custom transformer - AlgorithmDataTransformer:
#objc(AlgorithmDataTransformer)
public final class AlgorithmDataTransformer: ValueTransformer {
override public func transformedValue(_ value: Any?) -> Any? {
guard let array = value as? [Algorithm] else { return nil }
do {
return try NSKeyedArchiver.archivedData(withRootObject: array, requiringSecureCoding: true)
} catch {
assertionFailure("Failed to transform `Algorithm` to `Data`")
return nil
}
}
override public func reverseTransformedValue(_ value: Any?) -> Any? {
guard let data = value as? NSData else { return nil }
do {
return try NSKeyedUnarchiver.unarchivedArrayOfObjects(ofClass: Algorithm.self, from: data as Data)
} catch {
assertionFailure("Failed to transform `Data` to `Algorithm`")
return nil
}
}
}
extension AlgorithmDataTransformer {
/// The name of the transformer. This is the name used to register the transformer using `ValueTransformer.setValueTrandformer(_"forName:)`.
static let name = NSValueTransformerName(rawValue: String(describing: AlgorithmDataTransformer.self))
/// Registers the value transformer with `ValueTransformer`.
public static func register() {
let transformer = AlgorithmDataTransformer()
ValueTransformer.setValueTransformer(transformer, forName: name)
}
}