动态的JSON解码Swift 4

Question

我正在尝试在Swift 4中解码以下JSON：

{
    "token":"RdJY3RuB4BuFdq8pL36w",
    "permission":"accounts, users",
    "timout_in":600,
    "issuer": "Some Corp",
    "display_name":"John Doe",
    "device_id":"uuid824fd3c3-0f69-4ee1-979a-e8ab25558421"
}

问题是，JSON中的最后两个元素（display_name和device_id）可能存在或可能不存在，或者这些元素可以被命名为完全不同但仍然未知的内容，即"fred": "worker", "hours" : 8

因此，我要实现的目标是解码已知的内容，即token，permission，timeout_in和issuer以及任何其他元素（display_name，device_id等）将它们放入字典中。

我的结构看起来像这样：

struct AccessInfo : Decodable
{
    let token: String
    let permission: [String]
    let timeout: Int
    let issuer: String
    let additionalData: [String: Any]
    private enum CodingKeys: String, CodingKey
    {
        case token
        case permission
        case timeout = "timeout_in"
        case issuer
    }
    public init(from decoder: Decoder) throws
    {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        token = container.decode(String.self, forKey: .token)
        permission = try container.decodeIfPresent(String.self, forKey: .permission).components(separatedBy: ",")
        timeout = try container.decode(Int.self, forKey: . timeout)
        issuer = container.decode(String.self, forKey: .issuer)
        // This is where I'm stuck, how do I add the remaining
        // unknown JSON elements into additionalData?
    }
}
// Calling code, breviated for clarity
let decoder = JSONDecoder()
let accessInfo = try decoder.decode(AccessInfo.self, from: data!)

能够解码已知结构的一部分，如果有人可以提供一些指导，我可以在其中包含动态信息。

谢谢

Answer 1

受@matt评论的启发，这是我使用的完整示例。我扩展了KeyedDecodingContainer以解码未知密钥并提供一个参数以滤除已知的CodingKeys。

示例JSON

{
    "token":"RdJY3RuB4BuFdq8pL36w",
    "permission":"accounts, users",
    "timout_in":600,
    "issuer": "Some Corp",
    "display_name":"John Doe",
    "device_id":"uuid824fd3c3-0f69-4ee1-979a-e8ab25558421"
}

Swift Structs

struct AccessInfo : Decodable
{
    let token: String
    let permission: [String]
    let timeout: Int
    let issuer: String
    let additionalData: [String: Any]
    private enum CodingKeys: String, CodingKey
    {
        case token
        case permission
        case timeout = "timeout_in"
        case issuer
    }
    public init(from decoder: Decoder) throws
    {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        token = container.decode(String.self, forKey: .token)
        permission = try container.decode(String.self, forKey: .permission).components(separatedBy: ",")
        timeout = try container.decode(Int.self, forKey: . timeout)
        issuer = container.decode(String.self, forKey: .issuer)
        // Additional data decoding
        let container2 = try decoder.container(keyedBy: AdditionalDataCodingKeys.self)
        self.additionalData = container2. decodeUnknownKeyValues(exclude: CodingKeys.self)
    }
}
private struct AdditionalDataCodingKeys: CodingKey
{
    var stringValue: String
    init?(stringValue: String)
    {
        self.stringValue = stringValue
    }
    var intValue: Int?
    init?(intValue: Int)
    {
        return nil
    }
}

keyeddecodingcontainer扩展

extension KeyedDecodingContainer where Key == AdditionalDataCodingKeys
{
    func decodeUnknownKeyValues<T: CodingKey>(exclude keyedBy: T.Type) -> [String: Any]
    {
        var data = [String: Any]()
        for key in allKeys
        {
            if keyedBy.init(stringValue: key.stringValue) == nil
            {
                if let value = try? decode(String.self, forKey: key)
                {
                    data[key.stringValue] = value
                }
                else if let value = try? decode(Bool.self, forKey: key)
                {
                    data[key.stringValue] = value
                }
                else if let value = try? decode(Int.self, forKey: key)
                {
                    data[key.stringValue] = value
                }
                else if let value = try? decode(Double.self, forKey: key)
                {
                    data[key.stringValue] = value
                }
                else if let value = try? decode(Float.self, forKey: key)
                {
                    data[key.stringValue] = value
                }
                else
                {
                    NSLog("Key %@ type not supported", key.stringValue)
                }
            }
        }
        return data
    }
}

调用代码

let decoder = JSONDecoder()
let accessInfo = try decoder.decode(AccessInfo.self, from: data!)
print("Token: (accessInfo.token)")
print("Permission: (accessInfo.permission)")
print("Timeout: (accessInfo.timeout)")
print("Issuer: (accessInfo.issuer)")
print("Additional Data: (accessInfo.additionalData)")

输出

Token: RdJY3RuB4BuFdq8pL36w
Permission: ["accounts", "users"]
Timeout: 600
Issuer: "Some Corp"
Additional Data: ["display_name":"John Doe", "device_id":"uuid824fd3c3-0f69-4ee1-979a-e8ab25558421"]

Answer 2

这个问题实际上是Swift 4的重复，直到解码时间才能清楚地解码。一旦您理解构建岩石底部最小编码键采用器结构的技巧，您就可以将其用于任何字典。

在这种情况下，您将使用键控容器的allKeys获取未知的JSON字典键。

要证明，我将把自己仅限于JSON词典的完全未知部分。想象一下这个JSON：

let j = """
{
    "display_name":"John Doe",
    "device_id":"uuid824fd3c3-0f69-4ee1-979a-e8ab25558421"
}
"""
let jdata = j.data(using: .utf8)!

假定我们不知道该词典中有什么，除了它具有字符串键和字符串值的事实。因此，我们想在不知道其键的情况下解析jdata。

因此，我们有一个由一个字典属性组成的结构：

struct S {
    let stuff : [String:String]
}

现在的问题是如何将JSON分析到该结构 - 即如何使该结构符合可解码并处理该JSON。

这是：

struct S : Decodable {
    let stuff : [String:String]
    private struct CK : CodingKey {
        var stringValue: String
        init?(stringValue: String) {
            self.stringValue = stringValue
        }
        var intValue: Int?
        init?(intValue: Int) {
            return nil
        }
    }
    init(from decoder: Decoder) throws {
        let con = try! decoder.container(keyedBy: CK.self)
        var d = [String:String]()
        for key in con.allKeys {
            let value = try! con.decode(String.self, forKey:key)
            d[key.stringValue] = value
        }
        self.stuff = d
    }
}

现在我们解析：

let s = try! JSONDecoder().decode(S.self, from: jdata)

我们得到了一个s实例，其 stuff是这个词典：

["device_id": "uuid824fd3c3-0f69-4ee1-979a-e8ab25558421", "display_name": "John Doe"]

这就是我们想要的结果。