json - 预期解码 Dictionary 但发现一个数组而不是嵌套容器

Question

因此，我尝试使用 Codable 协议(protocol)解析此 JSON: https://randomuser.me/api/?results=100

这基本上是 100 个随机用户。

这是来自解码器的我的用户类初始化器，我需要它，因为用户是核心数据模型中的一个实体:

required convenience public init(from decoder: Decoder) throws {
        let managedObjectContext = CoreDataStack.sharedInstance.persistentContainer.viewContext
        guard let entity = NSEntityDescription.entity(forEntityName: "User", in: managedObjectContext) else {
                fatalError("Failed to decode User")
        }

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

        let container = try decoder.container(keyedBy: CodingKeys.self)
        let results = try container.nestedContainer(keyedBy: CodingKeys.self, forKey: .results)
        let name = try results.nestedContainer(keyedBy: CodingKeys.self, forKey: .name)
        firstName = try name.decode(String.self, forKey: .firstName)
        lastName = try name.decode(String.self, forKey: .lastName)

        let location = try results.nestedContainer(keyedBy: CodingKeys.self, forKey: .location)
        let street = try location.decode(String.self, forKey: .street)
        let city = try location.decode(String.self, forKey: .city)
        let postcode = try location.decode(String.self, forKey: .postcode)
        address = street + ", " + city + ", " + postcode

        email = try results.decode(String.self, forKey: .email)

        let pictures = try results.nestedContainer(keyedBy: CodingKeys.self, forKey: .pictures)
        pictureURL = try pictures.decode(String.self, forKey: .pictureURL)
    }

这是有缺陷的线路:

let results = try container.nestedContainer(keyedBy: CodingKeys.self, forKey: .results)

这是完整的错误:

typeMismatch(Swift.Dictionary<Swift.String, Any>, Swift.DecodingError.Context(codingPath: [], debugDescription: "Expected to decode Dictionary<String, Any> but found an array instead.", underlyingError: nil))

我认为这是由于 JSON 的结构所致，它是键“结果”下的 100 个元素的数组，我认为问题可能出在将它们全部组合在一起时。我该如何处理？

Answer 1

错误很明显:results 的值是一个数组，而 nestedContainers 需要一个字典。

要解码用户数组，您需要核心数据类之外的伞形结构。

struct Root : Decodable {
   let results: [User]
}

在解码 Root 时，为每个数组项调用 User 中的 init 方法。

要使用 nestedContainers，您必须将 CodingKey 分开。

这是没有 Core Data 内容的 init 方法。 postcode 可以是 String 或 Int

private enum CodingKeys: String, CodingKey { case name, location, email, picture }
private enum NameCodingKeys: String, CodingKey { case first, last }
private enum LocationCodingKeys: String, CodingKey { case street, city, postcode }
private enum PictureCodingKeys: String, CodingKey { case large, medium, thumbnail }

required convenience public init(from decoder: Decoder) throws {
    let container = try decoder.container(keyedBy: CodingKeys.self)
    let nameContainer = try container.nestedContainer(keyedBy: NameCodingKeys.self, forKey: .name)
    let firstName = try nameContainer.decode(String.self, forKey: .first)
    let lastName = try nameContainer.decode(String.self, forKey: .last)

    let locationContainer = try container.nestedContainer(keyedBy: LocationCodingKeys.self, forKey: .location)
    let street = try locationContainer.decode(String.self, forKey: .street)
    let city = try locationContainer.decode(String.self, forKey: .city)
    let postcode : String
    do {
        let postcodeInt = try locationContainer.decode(Int.self, forKey: .postcode)
        postcode = String(postcodeInt)
    } catch DecodingError.typeMismatch {
        postcode = try locationContainer.decode(String.self, forKey: .postcode)
    }
    let address = street + ", " + city + ", " + postcode

    let email = try container.decode(String.self, forKey: .email)

    let pictureContainer = try container.nestedContainer(keyedBy: PictureCodingKeys.self, forKey: .picture)
    let pictureURL = try pictureContainer.decode(URL.self, forKey: .large)
}