SwiftUI macOS JSON 转换为 class Codable

Question

I get the following json from an api call but am having trouble making the proper structure in swift and then getting the data as an array.

JSON:

{
   "status":"ok",
   "users":[
      {
         "position":0,
         "user":{
            "pk":"",
            "full_name":"",
            "username":"",
            "profile_pic_url":""
         }
      },...
   ]
}

Swift:

class Response: Codable {
    var status: String
    var users: [User]?
}

class User: Identifiable, Codable {
    var uuid = UUID()
    
    var pk: String
    var full_name: String
    var username: String
    var profile_pic_url: String
    
    enum CodingKeys: String, CodingKey {
        case
        pk = "user.pk",
        full_name = "user.full_name",
        username = "user.username",
        profile_pic_url = "user.profile_pic_url"
    }
}

class Fetch: ObservableObject {
    @Published var results = [User]()
    @Published var resultState = false
    @Published var errorState = false
    init(url: String) {
        self.results = []
        let url = URL(string: url)!
        URLSession.shared.dataTask(with: url) { data, response, error in
            do {
                if let data = data {
                    let results = try JSONDecoder().decode(Response.self, from: data)
                    DispatchQueue.main.async {
                        self.results = results.users ?? []
                        self.resultState = true
                    }
                    print("Widget: Ok.")
                } else {
                    self.results = []
                    self.resultState = true
                    print("Widget: No data.")
                }
            } catch {
                self.errorState = true
                self.resultState = true
                print("Widget: Error", error)
            }
        }.resume()
    }
}

Code:

@ObservedObject var fetch = Fetch(url: "")

List(fetch.results) { user in
    UserItem(user: user)
}

The problem is that inside array users, it contains an object, this object contains two elements a position attribute and then the user object.

What I think I'm doing wrong is taking the user object.

Can anyone help me out?

Edit:

struct Response: Codable {
    let status: String
    let users: [UserType]?
}

struct UserType: Codable {
    let position: Int
    let user: User
}

struct User: Codable {
    let pk: String
    let full_name: String
    let username: String
    let profile_pic_url: String
    enum CodingKeys: String, CodingKey {
        case pk, full_name, username, profile_pic_url
    }
}

class Fetch: ObservableObject {
    @Published var results = [User]()
    @Published var resultState = false
    @Published var errorState = false
    init(url: String) {
        self.results = []
        let url = URL(string: url)!
        URLSession.shared.dataTask(with: url) { data, response, error in
            do {
                if let data = data {
                    let results = try JSONDecoder().decode(Response.self, from: data)
                    let users = results.users?.map { $0.user }
                    DispatchQueue.main.async {
                        self.results = users ?? []
                        self.resultState = true
                    }
                    print("Widget: Ok.")
                } else {
                    self.results = []
                    self.resultState = true
                    print("Widget: No data.")
                }
            } catch {
                self.errorState = true
                self.resultState = true
                print("Widget: Error", error)
            }
        }.resume()
    }
}

        List(fetch.results) { user in
            UserItem(user: user)
        }

Answer 1

You need an extra struct that holds the User type

struct UserType: Codable {
    let position: Int
    let user: User
}

Meaning the top type becomes

struct Response: Codable {
    let status: String
    let users: [UserType]?
}

You also need to change the CodingKeys enum since it should just contain the property names which mean the enum can be written as

enum CodingKeys: String, CodingKey {
    case pk, full_name, username, profile_pic_url
}

For completeness here is the full User type

struct User: Identifiable, Codable {
    var uuid = UUID()

    var pk: String
    var full_name: String
    var username: String
    var profile_pic_url: String

    enum CodingKeys: String, CodingKey {
        case pk, full_name, username, profile_pic_url
    }
}

and when decoding then you can extract the users array with the map function

do {
    let results = try JSONDecoder().decode(Response.self, from: data)
    let users = results.users?.map { $0.user }
    ....

Note that I changed from class to struct because struct is better suited for this but class works as well. I also wonder why the users property is optional, I didn't change that but can the array really be nil?

Answer 2

You can try this.

    struct Response: Codable {
    let status: String 
    let users: [UserWPosition]
    
    var userNoPositions: [UserInfo] { // computed value with only array of userinfo
        users.compactMap { $0.user }
    }
}

// MARK: - User with position object
struct UserWPosition: Codable {
    let position: Int  // commenting this will also do no effect
    let user: UserInfo
}

// MARK: - UserInfo
struct UserInfo: Codable {
    let pk, fullName, username, profilePicURL: String
    enum CodingKeys: String, CodingKey {
        case pk
        case fullName = "full_name"
        case username
        case profilePicURL = "profile_pic_url"
    }
}

Read the comments I added to the code decoding will not code a key that's not added to the struct so commenting out position will have no issue also, the hierarchy of it should be like this now I added a userNoPositions computed value in response to give array of users easily.
Simply to access the array without positions

var resp =  try! JSONDecoder().decode(Response.self, from: encoded)  // encoded is the data from json   
print(resp.userNoPositions) // the array