Swift 4 JSON 解码根数组

Question

我在使用 Swift 4 解码功能解码 JSON 响应时遇到问题。 我有主结构，它有一个内部结构 var hr_employees: [Employee]? = []。问题是 JSON 没有映射 'var hr_employees: [Employee]？ = []。

我得到了三个根值 response_status、access_level、session_token 的正确值。

////////////////////////////////////////////////////////////

struct EmployeeData: Codable {
     var response_status:Int=0
     var access_level:Int=0
     var session_token:String=""
     var hr_employees: [Employee]? = []
}

private enum CodingKeys: String, CodingKey {
        case response_status="response_status"
        case access_level="access_level"
        case session_token="session_token"
        case hr_employees="hr_employees"
    }

    init() {

    }



init(from decoder: Decoder) throws {
            let values = try decoder.container(keyedBy: CodingKeys.self)
            response_status = try values.decode(Int.self, forKey: .response_status)
            do{
                session_token = try values.decode(String.self, forKey: .session_token)
            }catch {
                print( "No value associated with key title (\"session_token\").")
            }
            do{
                access_level = try values.decode(Int.self, forKey: .access_level)
            }
            catch {
                print( "No value associated with key access_level ")
            }
        }

///////////////内部结构///////////////////

  struct Employee: Codable {
        var userId:Int=0
        var nameFirst:String=""
        var nameLast:String=""
        var position:String=""
        var company:String=""
        var supervisor:String=""
        var assistant:String=""
        var phone:String=""
        var email:String=""
        var address:String=""
        var gender:String=""
        var age:Int=0
        var nationality:String=""
        var firstLanguage:String=""
        var inFieldOfView:String = "0"
        var photo:String="user-default"
        var status:String="3"
    }

///////////下面是JSON///////////////////

{
"response_status":1
,"access_level":2
,"hr_employees":[
{
"user_id":4226
,"name_last":"Sampe"
,"name_first":"Frederica"
,"position":"Systems Maint"
,"phone":"123456"
,"email":"omega@demo.mobile"
,"address":"00100 Helsinki 1"
,"age":67
,"company":"Omega Enterprise"
}
,{
"user_id":5656
,"name_last":"Aalto"
,"name_first":"Antero"
,"position":"Programming Methodology and Languages Researcher"
,"supervisor":"Mayo Georgia"
,"phone":"123456"
,"email":"omega@demo.mobile"
,"address":"00100 Finland "
,"age":51
,"company":"Omega Fire Related Equipment"
}
]
}

Answer 1

一个问题是 JSON 中的内容与您对 Employee 的定义不匹配。例如，nameFirst 不存在，name_first 存在。

另一个是你有一个init(from:) 的自定义实现，它永远不会获取hr_employees 值！

Answer 2

有很多事情需要你改进：

1. 您的Structs 可以改进以利用Codable 协议的自动化功能。
2. 您需要了解为什么要使用CodingKeys 枚举
   • 在你的情况下......也是最好的地方（提示：在Struct 本身内）
3. 您需要知道哪些参数需要是可选的以及为什么
   • 这当然取决于你的 json 结构
4. 如果参数要具有默认值，那么您需要遵循一个完全不同的过程；就像拥有自己的init(from:Decoder)
   • 您在一定程度上需要，但并不能真正处理当前状态下的所有内容

---

根据您给定的 JSON 示例，您可以简单地执行以下操作。
但是...请注意，这并非旨在提供默认值。即，如果 json 中缺少某个键，例如 status，那么 Employee 结构中的参数 status 将是 nil，而不是默认值 "3"。

struct EmployeeData: Codable {
    var responseStatus: Int
    var accessLevel: Int

    /*
     sessionToken is optional because as per your JSON
     it seems it not always available
     */
    var sessionToken: String?

    var hrEmployees: [Employee]

    /*
     CodingKeys is inside the struct
     It's used if the JSON key names are different than
     the ones you plan to use.
     i.e. JSON has keys in snake_case but we want camelCase
     */
    enum CodingKeys: String, CodingKey {
        case responseStatus = "response_status"
        case accessLevel = "access_level"
        case sessionToken = "session_token"
        case hrEmployees = "hr_employees"
    }
}

---

struct Employee: Codable {
    var userId: Int
    var nameFirst: String
    var nameLast: String
    var position: String
    var company: String
    var supervisor: String?
    var assistant: String?
    var phone: String
    var email: String
    var address: String
    var gender: String?
    var age: Int
    var nationality: String?
    var firstLanguage: String?
    var inFieldOfView: String?
    var photo: String?
    var status: String?

    enum CodingKeys: String, CodingKey {
        case userId = "user_id"
        case nameFirst = "name_first"
        case nameLast = "name_last"
        case firstLanguage = "first_language"
        case inFieldOfView = "in_field_of_view"

        /*
         Keys names that are same in json as well as in your
         model need not have a raw string value
         but must be defined if it's to be encoded/decoded
         from the json else it can be omitted and a default
         value will be required which won't affect the encoding
         or decoding process
         */
        case position
        case company
        case supervisor
        case assistant
        case phone
        case email
        case address
        case gender
        case age
        case nationality
        case photo
        case status
    }
}

---

检查：

do {
    let employeeData = try JSONDecoder().decode(EmployeeData.self,
                                                from: jsonAsData)
    print(employeeData)
}
catch {
    /*
     If it comes here then debug, it's most probably nil keys
     meaning you need more optional parameters in your struct
     */
    print(error)
}

---

如果你想在你的Struct 中使用默认值，而上面的例子对你来说是一个破坏者，那么请检查以下答案：

• https://stackoverflow.com/a/44575580/2857130