json - Swift 4 Codable; How to decode object with single root-level key

Question

I'm using the Swift 4 Codable protocol with JSON data. My data is formatted such that there is a single key at the root level with an object value containing the properties I need, such as:

{
  "user": {
    "id": 1,
    "username": "jdoe"
  }
}

I have a User struct that can decode the user key:

struct User: Codable {
  let id: Int
  let username: String
}

Since id and username are properties of user, not at the root level, I needed to make a wrapper type like so:

struct UserWrapper: Codable {
  let user: User
}

I can then decode the JSON via the UserWrapper, and the User is decoded also. It seems like a lot of redundant code since I'll need an extra wrapper on every type I have. Is there a way to avoid this wrapper pattern or a more correct/elegant way of handling this situation?

Answer 1

You could decode using a dictionary: user combination then extract out the user object. e.g.

struct User: Codable {
    let id: Int
    let username: String
}

let decoder = JSONDecoder()
let userDictionary = try decoder.decode([String: User].self, from: jsonData)