使用Codable保存到String的CoreData数组中

Question

我被卡住了。我有json（电影数组）。我正在尝试使用Codable协议解析它，并保存到Core Data。问题是Movie对象具有流派数组（字符串数组）。我创建了两个实体：电影和流派（关系一对多）。解析Movie对象没有问题，但是当我尝试解析流派时-它不起作用。

有什么想法吗？

P.S。是的，我知道类型数组没有键“名称”。

{
"title": "Dawn of the Planet of the Apes",
"image": "https://api.androidhive.info/json/movies/1.jpg",
"rating": 8.3,
"releaseYear": 2014,
"genre": ["Action", "Drama", "Sci-Fi"]
},
{
"title": "District 9",
"image": "https://api.androidhive.info/json/movies/2.jpg",
"rating": 8,
"releaseYear": 2009,
"genre": ["Action", "Sci-Fi", "Thriller"]
}

电影模式：

@objc(Movie)
class Movie: NSManagedObject, Decodable {

    @NSManaged var title: String?
    @NSManaged var image: String?
    @NSManaged var rating: Float
    @NSManaged var releaseYear: Int
    @NSManaged var genres: Set<Genre>?

    enum apiKey: String, CodingKey {
        case title
        case image
        case rating
        case releaseYear
        case genres = "genre"
    }

    @nonobjc public class func request() -> NSFetchRequest<Movie> {
        return NSFetchRequest<Movie>(entityName: "Movie")
    }

    // MARK: - Decodable

    public required convenience init(from decoder: Decoder) throws {

        guard let contextUserInfoKey = CodingUserInfoKey.context,
            let manageObjContext = decoder.userInfo[contextUserInfoKey] as? NSManagedObjectContext,
            let manageObjMovie = NSEntityDescription.entity(forEntityName: "Movie", in: manageObjContext) else {
            fatalError("Error to getting context")
        }

        self.init(entity: manageObjMovie, insertInto: manageObjContext)

        let container = try decoder.container(keyedBy: apiKey.self)
        self.title = try container.decodeIfPresent(String.self, forKey: .title)
        self.image = try container.decodeIfPresent(String.self, forKey: .image)
        self.rating = try container.decodeIfPresent(Float.self, forKey: .rating) ?? 0
        self.releaseYear = try container.decodeIfPresent(Int.self, forKey: .releaseYear) ?? 0

        self.genres = try container.decodeIfPresent(Set<Genre>.self, forKey: .genres) ?? []        
    }
}

// MARK: Generated accessors for geonames
extension Movie {

    @objc(addGenresObject:)
    @NSManaged func addToGenres(_ value: Genre)

    @objc(setKeyObject:)
    @NSManaged func setKeyObject(_ value: String)
}

流派模型：

@objc(Genre)
class Genre: NSManagedObject, Decodable {

    @NSManaged var name: String?

    enum apiKey: String, CodingKey {
        case name
    }

    @nonobjc public class func request() -> NSFetchRequest<Genre> {
        return NSFetchRequest<Genre>(entityName: "Genre")
    }

    // MARK: - Decodable

    public required convenience init(from decoder: Decoder) throws {

        guard let contextUserInfoKey = CodingUserInfoKey.context,
            let manageObjContext = decoder.userInfo[contextUserInfoKey] as? NSManagedObjectContext,
            let manageObjGenre = NSEntityDescription.entity(forEntityName: "Genre", in: manageObjContext) else {
            fatalError("Error to getting context")
        }

        self.init(entity: manageObjGenre, insertInto: manageObjContext)

        let container = try decoder.container(keyedBy: apiKey.self)
        self.name = try container.decodeIfPresent(String.self, forKey: .name)
    }
}

Answer 1

您需要与Movie中的Genre成反比关系。添加此

@NSManaged var movie: Movie?

并在模型文件中建立连接。

然后解码一个字符串数组，将其映射到Genre实例，并在init方法的末尾将self分配给该关系

let genreData = try container.decodeIfPresent([String].self, forKey: .genres) ?? []
let genreArray = genreData.map { name in
    let genre = Genre(context: manageObjContext)
    genre.name = name
    genre.movie = self
    return genre
}
self.genres = Set(genreArray)

也考虑使用从Genre到Movie的多对多关系，因为否则，您将有很多具有相同名称的Genre实例。并考虑减少Core Data类中的可选参数。似乎JSON源始终提供所有字段。您可以摆脱很多多余的代码。