在 API 请求中实现 Swift Result<Success, Error> 时遇到问题

Question

我有意创建一个已存在于 MongoDB 中的用户，以向用户显示错误消息，例如“请选择其他用户名”或“电子邮件已在使用中”，但我无法解码服务器的响应。

我的模型旨在处理成功（用户/令牌）或错误响应（消息）...

当在后端创建帐户时，我能够成功解码用户对象...

我做错了什么？我觉得我应该以某种方式为错误模型使用枚举？？

// POSTMAN RESPONSE WHEN USERNAME ALREADY TAKEN
{
    "success": false,
    "message": "Please choose a different username"
}

// XCODE ERROR MESSAGE 

//...Expected to decode Dictionary<String, Any> but found a string/data 
//instead.", underlyingError: nil))

// DATA MODELS

struct UserResponse: Decodable {
    let success: Bool
    let message: ErrorResponse?
    var user: User?
    var token: String?
}

struct ErrorResponse: Decodable, Error {
    let message: String
}

class LoginService {
    
     static func createAccount(username: String, email: String, password: String, 
completion: @escaping(Result <UserResponse, Error>) -> Void) {
     
        let user = UserSignup(username: username, email: email, password: password)
        
        // Create URL code
       
        do {
            let encoder = JSONEncoder()
            urlRequest.httpBody = try encoder.encode(user)
           
            let dataTask = URLSession.shared.dataTask(with: urlRequest) { data, response, error in
               
                if let error = error {
                    completion(.failure(error))
                    return
                }
                guard let jsonData = data else { return }
    
                do {
                    let responseObject = try JSONDecoder().decode(UserResponse.self, from: jsonData)
                    switch responseObject.success {
                    case true:
                        completion(.success(responseObject))
                    case false:
                        // not working
                        guard let errorMessage = responseObject.message else {
                          return
                        }
                        completion(.failure(errorMessage))
                    }
                } catch {
                    print(error)
                }
            }
            dataTask.resume()
        } catch {
            // handle error
        }
    }

Answer 1

错误显示message 是一个字符串，因此将其声明为String

struct UserResponse: Decodable {
    let success: Bool
    let message: String?
    var user: User?
    var token: String?
}

我觉得我应该以某种方式为错误模型使用枚举

摆脱可选项是个好主意。枚举首先解码status，然后根据值解码成功时的user 和token，失败时解码错误message

struct UserResponse {
    let user: User
    let token: String
}

enum Response : Decodable {
    case success(UserResponse)
    case failure(String)
    
    private enum CodingKeys : String, CodingKey { case success, message, user, token }
    
    init(from decoder : Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        let success = try container.decode(Bool.self, forKey: .success)
        if success {
            let user = try container.decode(User.self, forKey: .user)
            let token = try container.decode(String.self, forKey: .token)
            self = .success(UserResponse(user: user, token: token))
        } else {
            let message = try container.decode(String.self, forKey: .message)
            self = .failure(message)
        }
    }
}

然后你可以替换

   let responseObject = try JSONDecoder().decode(UserResponse.self, from: jsonData)
    switch responseObject.success {
    case true:
        completion(.success(responseObject))
    case false:
        // not working
        guard let errorMessage = responseObject.message else {
          return
        }
        completion(.failure(errorMessage))
    }

与

   let response = try JSONDecoder().decode(Response.self, from: jsonData)
    switch response {
    case .success(let responseObject):
        completion(.success(responseObject))
    case .failure(let errorMessage)
        completion(.failure(errorMessage))
    }