Swift Json 解码嵌套数组/字典到平面 model

Question

I am trying to decode the following json object to my User model in Swift.

My issue is decoding the values _id and token out of the tokens array, where the first token in the array contains the values I want to decode into User.tokenId and User.token.

I am trying to extract/map the values directly into my User model struct without having another nested struct in my User model ( such as struct Token { var id: String, var token: String } )

let json = """
    {
        "currentLocation": {
            "latitude": 0,
            "longitude": 0
        },
        "profileImageUrl": "",
        "bio": "",
        "_id": "601453e4aae564fc19075b68",
        "username": "johnsmith",
        "name": "john",
        "email": "johnsmith@gmail.com",
        "keywords": ["word", "weds"],
        "tokens": [
            {
                "_id": "213453e4aae564fcqu775b69",
                "token": "eyJhbGciOiJIUzqoNiIsInR5cCI6IkpXVCJ9.eyJfaWQiOiI2MDE0NTNlNGFhZTU2NGZjMTkwNzViNjgiLCJpYXQiOjE2MTE5NDQ5MzIsImV4cCI6MTYxMjM3NjkzMn0.PbTsA3B0MAfcVvEF1UAMhUXFiqIL1FcxVFGgMTZ5HCk"
            }
        ],
        "createdAt": "2021-01-29T18:28:52.845Z",
        "updatedAt": "2021-01-29T18:28:52.883Z"
    }
    """.data(using: .utf8)!


struct User: Codable {
    var latitude: Double 
    var longitude: Double 
    var profileImageUrl: String 
    var bio: String 
    var userId: String 
    var username: String
    var name: String
    var email: String
    var keywords: [String]
    var tokenId: String
    var token: String
    var createdAt: Date
    var updatedAt: Date
    
    private enum UserKeys: String, CodingKey {
        case currentLocation
        case profileImageUrl
        case bio
        case userId = "_id"
        case username
        case name
        case email
        case keywords
        case tokens
        case createdAt
        case updatedAt
    }
    
    private enum CurrentLocationKeys: String, CodingKey { 
        case latitude
        case longitude
    }
    
    private enum TokenKeys: String, CodingKey {
        case tokenId = "_id"
        case token
    }
    
    init(from decoder: Decoder) throws {
        
        let userContainer = try decoder.container(keyedBy: UserKeys.self)
              let currentLocationContainer = try userContainer.nestedContainer(keyedBy: CurrentLocationKeys.self, forKey: .currentLocation) 
              self.latitude = try currentLocationContainer.decode(Double.self, forKey: .latitude)
              self.longitude = try currentLocationContainer.decode(Double.self, forKey: .longitude)
            self.profileImageUrl = try userContainer.decode(String.self, forKey: .profileImageUrl)
            self.bio = try userContainer.decode(String.self, forKey: .bio)
            self.userId = try userContainer.decode(String.self, forKey: .userId)
            self.username = try userContainer.decode(String.self, forKey: .username)
            self.name = try userContainer.decode(String.self, forKey: .name)
            self.email = try userContainer.decode(String.self, forKey: .email)
            self.keywords = try userContainer.decode([String].self, forKey: .keywords)
              let tokensContainer = try userContainer.nestedContainer(keyedBy: TokenKeys.self, forKey: .tokens)
              self.tokenId = try tokensContainer.decode(String.self, forKey: .tokenId)
              self.token = try tokensContainer.decode(String.self, forKey: .token)
            self.createdAt = try userContainer.decode(Date.self, forKey: .createdAt)
            self.updatedAt = try userContainer.decode(Date.self, forKey: .updatedAt)
    }
}

let user = try! decoder.decode(User.self, from: json)

Answer 1

First of all I assume that your decoder has an appropriate date decoding strategy to be able to decode the ISO8601 strings to Date .

The enclosing container of the token dictionary is an array. You have to insert an intermediate nestedUnkeyedContainer

...
var arrayContainer = try userContainer.nestedUnkeyedContainer(forKey: .tokens)
let tokensContainer = try arrayContainer.nestedContainer(keyedBy: TokenKeys.self)
self.tokenId = try tokensContainer.decode(String.self, forKey: .tokenId)
self.token = try tokensContainer.decode(String.self, forKey: .token)
...

It's much less code to decode the JSON into multiple structs