Swift Json decoding nested array / dictionary to flat model - ios

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