How to save custom type in CoreData with Codable Protocol Swift

Question

I am trying to save the custom object of type codable, In which I am able to store Int16 type. But for [Movie] type in Coredata its NSObject, Entity I have an attribute movie is of type Transformable.

Error: No 'decodeIfPresent' candidates produce the expected contextual result type 'NSObject?'

How can save this custom type Array with Transformable type

class MovieResults: Results, Codable {

        required convenience public init(from decoder: Decoder) throws  {
            guard let codingUserInfoKeyManagedObjectContext = CodingUserInfoKey.context,
                let managedObjectContext = (UIApplication.shared.delegate as? AppDelegate)?.persistentContainer.viewContext,
                let entity = NSEntityDescription.entity(forEntityName: "Results", in: managedObjectContext) else {
                    fatalError("Failed to retrieve managed object context")
            }

            self.init(entity: entity, insertInto: managedObjectContext)

            let container = try decoder.container(keyedBy: CodingKeys.self)

            self.page = try container.decodeIfPresent(Int16.self, forKey: .page) ?? 0
            self.numberOfResults = try container.decodeIfPresent(Int16.self, forKey: .numberOfResults) ?? 0
            self.numberOfPages = try container.decodeIfPresent(Int16.self, forKey: .numberOfPages) ?? 0
            self.movies = try container.decodeIfPresent([Movie].self, forKey: .movies) ?? nil
        }

        // MARK: - Encodable
        public func encode(to encoder: Encoder) throws {
            var container = encoder.container(keyedBy: CodingKeys.self)
            try container.encode(page, forKey: .page)
            try container.encode(numberOfResults, forKey: .numberOfResults)
            try container.encode(numberOfPages, forKey: .numberOfPages)
            try container.encode(movies, forKey: .movies)
        }

        private enum CodingKeys: String, CodingKey {
            case page
            case numberOfResults = "total_results"
            case numberOfPages = "total_pages"
            case movies = "results"
        }
    }

Movie Array is an custom attribute of type Transformable in CoreData

class Movies: Movie, Codable {
    public func encode(to encoder: Encoder) throws {

    }

    required convenience init(from decoder: Decoder) throws {
        guard let codingUserInfoKeyManagedObjectContext = CodingUserInfoKey.context,
            let managedObjectContext = decoder.userInfo[codingUserInfoKeyManagedObjectContext] as? NSManagedObjectContext,
            let entity = NSEntityDescription.entity(forEntityName: "Movie", in: managedObjectContext) else {
                fatalError("Failed to decode User")
        }

        self.init(entity: entity, insertInto: managedObjectContext)

        let container = try decoder.container(keyedBy: CodingKeys.self)

        self.identifier = try container.decodeIfPresent(Int16.self, forKey: .identifier) ?? 0
        self.posterPath = try container.decodeIfPresent(String.self, forKey: .identifier)
        self.backdrop = try container.decodeIfPresent(String.self, forKey: .identifier)
        self.title = try container.decodeIfPresent(String.self, forKey: .identifier)
        self.releaseDate = try container.decodeIfPresent(String.self, forKey: .identifier)
        self.rating = try container.decodeIfPresent(Int16.self, forKey: .rating) ?? 0
        self.overview = try container.decodeIfPresent(String.self, forKey: .identifier)
    }

    enum CodingKeys: String, CodingKey {
        case identifier
        case posterPath = "poster_path"
        case backdrop = "backdrop_path"
        case title
        case releaseDate = "release_date"
        case rating = "vote_average"
        case overview
    }
}

With this, it's working fine.

self.movies = try container.decodeIfPresent([Movies].self, forKey: .movies)! as NSObject

I am Inheriting NSManagedObject Class Is this Correct way. I tried using the extension but it throws an error for initializers.?

public convenience init(from decoder: Decoder) throws

Initializer requirement 'init(from:)' can only be satisfied by a 'required' initializer in the definition of non-final class 'MovieResult'

@VaibhavParmar Error: No 'decodeIfPresent' candidates produce the expected contextual result type 'NSObject?' — salman siddiqui
Share with us your Movie class declaration and decoder implementation (if any). Also, is "movies" an attribute or a relationship? — staticVoidMan
@VaibhavParmar I have Edited and movies is an Array Attribute of Transformable type. — salman siddiqui
@VaibhavParmar Thx it works fine for encode. But using force unwrap is a good way..? — salman siddiqui

Vaibhav Parmar Vaibhav Parmar · Accepted Answer · 2019-02-04T06:00:17

I think this could be done in a more simpler way. Here is how you can give a try. Here is MovieResult class [It's good to have the name of the class in singular].

public class MovieResult: Codable {
    public var stringVariable: String
    public var intVariable: Int

    public init(stringVariable: String, intVariable: Int) {
        self.stringVariable = stringVariable
        self.intVariable = intVariable
    } 
}

Here you can persist MovieResult in UserDefaults.

public var savedMovieResult: MovieResult? {
    get {
        let data = UserDefaults.standard.object(forKey: "savedMovieResultKey") as? Data
        var movieResult: MovieResult?
        if let data = data {
            do {
                movieResult = try PropertyListDecoder().decode(MovieResult.self, from: data)
            } catch {
                print(error)
            }
        }
        return movieResult
    } set {
        do {
            try UserDefaults.standard.set(PropertyListEncoder().encode(newValue), forKey: "savedMovieResultKey")
            UserDefaults.standard.synchronize()
        } catch {
            print(error)
        }
    }
}

How to save custom type in CoreData with Codable Protocol Swift

1 Answers