Codable object mapping array element to string - ios

Question

I have a (annoying) situation where my back-end returns an object like this:
{
"user": {
"name": [
"John"
],
"familyName": [
"Johnson"
]
}
}
where each property is an array that holds a string as its first element. In my data model struct I could declare each property as an array but that really would be ugly. I would like to have my model as such:
struct User: Codable {
var user: String
var familyName: String
}
But this of course would fail the encoding/decoding as the types don't match. Until now I've used ObjectMapper library which provided a Map object and currentValue property, with that I could declare my properties as String type and in my model init method assig each value through this function:
extension Map {
public func firstFromArray<T>(key: String) -> T? {
if let array = self[key].currentValue as? [T] {
return array.first
}
return self[key].currentValue as? T
}
}
But now that I am converting to Codable approach, I don't know how to do such mapping. Any ideas?

Answer 1

You can override init(from decoder: Decoder):
let json = """
{
"user": {
"name": [
"John"
],
"familyName": [
"Johnson"
]
}
}
"""
struct User: Codable {
var name: String
var familyName: String
init(from decoder: Decoder) throws {
let container:KeyedDecodingContainer = try decoder.container(keyedBy: CodingKeys.self)
let nameArray = try container.decode([String].self, forKey: .name)
let familyNameArray = try container.decode([String].self, forKey: .familyName)
self.name = nameArray.first!
self.familyName = familyNameArray.first!
}
enum CodingKeys: String, CodingKey {
case name
case familyName
}
}
let data = json.data(using: .utf8)!
let decodedDictionary = try JSONDecoder().decode(Dictionary<String, User>.self, from: data)
print(decodedDictionary) // ["user": __lldb_expr_48.User(name: "John", familyName: "Johnson")]
let encodedData = try JSONEncoder().encode(decodedDictionary["user"]!)
let encodedStr = String(data: encodedData, encoding: .utf8)
print(encodedStr!) // {"name":"John","familyName":"Johnson"}

Answer 2

My tendency would be to adapt your model to the data coming in and create computed properties for use in the application, e.g.
struct User: Codable {
var user: [String]
var familyName: [String]
var userFirstName: String? {
return user.first
}
var userFamilyName: String? {
return familyName.first
}
}
This allows you to easily maintain parody with the data structure coming in without the maintenance cost of overriding the coding/decoding.
If it goes well with your design, you could also have a UI wrapper Type or ViewModel to more clearly differentiate the underlying Model from it's display.