Custom Decodable JSON - Get first array element - ios

Question

I have JSON data that looks like this:
{
// Other attributes here....
"id": "a4s5d6f8ddw",
"images": {
"selection": [
{
"url": "https://www.myimage.com"
},
// ... more images here
]
}
}
I want to extract the id and the first url from the nested JSON and store it in my struct. I've tried something like this, but I can't quite get it:
struct MyImage {
let id: String
let url: URL
enum CodingKeys: CodingKey {
case id
case images
}
enum Selection: CodingKey {
case selection
}
enum ImageURL: CodingKey {
case url
}
}
extension MyImage: Decodable {
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
id = try values.decode(String.self, forKey: .id)
let selection = try values.nestedContainer(keyedBy: Selection.self, forKey: .selection)
// Then what?? Need to extract just the first one and then decode to a URL
}
How can I finish this off?

Answer 1

You're on the right track, but some minor errors:
struct MyImage {
let id: String
let url: URL
enum CodingKeys: CodingKey {
case id
case images
}
// Keys inside of Images
enum ImagesKeys: CodingKey {
case selection
}
// Struct inside of Selection
private struct Selection: Decodable {
let url: URL
}
}
With that, the decoder is close to what you were thinking:
extension MyImage: Decodable {
init(from decoder: Decoder) throws {
// Decode the outer stuff
let values = try decoder.container(keyedBy: CodingKeys.self)
id = try values.decode(String.self, forKey: .id)
// Pull off the images object
let images = try values.nestedContainer(keyedBy: ImagesKeys.self, forKey: .images)
// Extract the selections array
var selections = try images.nestedUnkeyedContainer(forKey: .selection)
// Take the first element
let firstSelection = try selections.decode(Selection.self)
// Done.
self.url = firstSelection.url
}
}