How can I decode response data if data is nested in Swift - swift

Question

I've got a problem with decoding response data. Here is my request function
#IBAction func onGetCities(_ sender: UIButton) {
guard let url = URL(string: "http://somelink.com/city-list") else { return }
var request = URLRequest(url: url)
request.httpMethod = "GET"
let session = URLSession.shared
let task = session.dataTask(with: request) { (data, response, error) in
print(JSON(data))
guard let data = data else { return }
do{
let cities = try JSONDecoder().decode([City].self, from: data)
print(cities)
}catch{
}
}
task.resume()
}
And City struct
struct City: Decodable {
let id: Int
let city: String
}
Here is the response data, I want to decode "items"
{
"offset": 0,
"limit": 10,
"items": [
{id: 0, name: "City name"},
{id: 1, name: "City name1"},
.....
]
}

Answer 1

You need to have nested structures that mirror your nested JSON:
struct City: Decodable {
let id: Int
let city: String
}
struct ResponseObject: Decodable {
let items: [City]
let offset: Int
let limit: Int
}
And then:
do {
let result = try JSONDecoder().decode(ResponseObject.self, from: data)
print(result)
let cities = result.items
print(cities)
} catch {
print(error)
}
Note, in your original example, you included a JSON key, updated_at which was the date represented in number of seconds since 1970 (standard UNIX representation). So, to decode that:
struct City: Decodable {
let id: Int
let city: String
}
struct ResponseObject: Decodable {
let items: [City]
let offset: Int
let limit: Int
let code: Int
let updatedAt: Date
enum CodingKeys: String, CodingKey {
case items, offset, limit, code
case updatedAt = "updated_at"
}
}
And then:
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .secondsSince1970
do {
let result = try decoder.decode(ResponseObject.self, from: data)
print(result)
let cities = result.items
print(cities)
} catch {
print(error)
}