如何使用 Codable 协议快速构建 json 对象模型

Question

I'm coding a REST Web app client and I use JSON which looks like this:

JSON1

{
  "device" : "iPhone"
  "manufacturer" : "Apple"
  "id" : 42

  "owner" : "Steve"
}

But the API could give me this kind of JSON also

JSON2

{
  "device" : "iPhone"
  "manufacturer" : "Apple"
  "id" : 42

  "latitude" : 3.1415926535
  "longitude" : 2.7182818284
}

So now in my app I create a struct who conforms to the Codable protocol

struct MyStruct : Codable {
  var name: String
  var manufacturer: String

  var owner: String?

  // I prefer to use a property of type Location rather than 2 variables
  var location: Location? {
    guard let latitude = latitude, let longitude = longitude else {
      return nil
    }

    return Location(latitude: latitude, longitude: longitude)
  }

  // Used to conform to the Codable protocol
  private var latitude: Double?
  private var longitude: Double?
}

struct Location {
  var latitude: Double = 0.0
  var longitude: Double = 0.0
}

This architecture works but it seems to me not the best one or elegant. Would you know if a better approach exists? Should I use 2 differents json model instead like:

struct MyStruct1 : Codable {
  var name: String
  var manufacturer: String
  var owner: String
}

struct MyStruct2 : Codable {
  var name: String
  var manufacturer: String

  private var latitude: Double
  private var longitude: Double
}

I'm new to REST API client and this kind of JSON doesn't seems to use a good architecture.

Answer 1

Make the owner , latitude & longitude properties optional. And use decodeIfPresent for decoding properties only when they exists.

You can create a struct as-

struct UserData: Codable {//Confroms to Codable protocol
    var id: Int
    var device: String
    var manufacturer: String
    var owner: String? = nil//Making property optional
    var latitude: Double? = nil//Making property optional
    var longitude: Double? = nil//Making property optional
    init(from decoder: Decoder) throws {
        let values = try decoder.container(keyedBy: CodingKeys.self)
        id = try values.decode(Int.self, forKey: .id)
        device = try values.decode(String.self, forKey: .device)
        manufacturer = try values.decode(String.self, forKey: .manufacturer)
        owner = try values.decodeIfPresent(String.self, forKey: .owner)
        latitude = try values.decodeIfPresent(Double.self, forKey: .latitude)
        longitude = try values.decodeIfPresent(Double.self, forKey: .longitude)
    }
}

Example Json:

    let jsonExample = """
 {
  "device" : "iPhone",
  "manufacturer" : "Apple",
  "id" : 42,
  "owner" : "Steve"
}
""".data(using: .utf8)!
    let jsonExample2 = """
 {
  "device" : "iPhone",
  "manufacturer" : "Apple",
  "id" : 42,
  "latitude" : 3.1415926535,
  "longitude" : 2.7182818284
}
""".data(using: .utf8)!.

Usage:

    //Decode struct using JSONDecoder
     let jsonDecoder = JSONDecoder()
            do {
                let modelResult = try jsonDecoder.decode(UserData.self,from: jsonExample2)
                print("owner is \(String(describing: modelResult.owner)) - latitude is \(String(describing: modelResult.latitude)) - longitude is \(String(describing: (modelResult.longitude)))")
            } catch {
                print(error)
            }