使用 Codable 保存到 CoreData 字符串数组

Question

我卡住了。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 对象有 Genres 数组（字符串数组）。我创建了两个实体：电影和流派（具有一对多关系）。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，我知道流派数组没有键 "name".

{
"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"]
}

电影模特：

@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 Genre 中的 Movie 成反比关系。添加这个

@NSManaged var movie: Movie?

并在模型文件中建立连接。

然后解码字符串数组，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)

考虑使用从 Genre 到 Movie 的一对多关系，否则您将有很多 Genre 个同名实例。并考虑减少核心数据类中的可选项。 JSON 源似乎总是提供所有字段。你可以摆脱很多冗余代码。

使用 Codable 保存到 CoreData 字符串数组

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