Array vs Dictionary response structures with JSONDecoder - swift

Question

Got the following data model:
class ResponseMultipleElements<Element: Decodable>: Decodable {
let statuscode: Int
let response_type: Int
let errormessage: String?
let detailresponse: Element?
}
class Element<T: Decodable>: Decodable {
let count: String;
let element: T?
}
For the following API response structure:
{
"statuscode": 200,
"response_type": 3,
"errormessage": null,
"detailresponse": {
"count": "1",
"campaigns": [
{
"id": 1,
"name": "Foo",
"targetagegroup": null,
"creator":...
...
}
}
}
I'm triggering JSONDecoder like this:
class APIService: NSObject {
func getCampaignList(completion: #escaping(Result<[Campaign], APIError>) -> Void) {
guard let endpoint = URL(string: apiBaseUrlSecure + "/campaignlist") else {fatalError()}
var request = URLRequest(url: endpoint)
request.addValue("Bearer " + UserDefaults.standard.string(forKey: "authtoken")!, forHTTPHeaderField: "Authorization")
request.httpMethod = "GET"
let dataTask = URLSession.shared.dataTask(with: request) { data, response, error in
guard let httpResponse = response as? HTTPURLResponse, httpResponse.statusCode == 200, let jsonData = data
else { print("ERROR: ", error ?? "unknown error"); completion(.failure(.responseError)); return }
do {
let response = try JSONDecoder().decode(ResponseMultipleElements<[Campaign]>.self, from: jsonData)
completion(.success(response.detailresponse!))
} catch {
print("Error is: ", error)
completion(.failure(.decodingError))
}
}
dataTask.resume()
}
...
}
And I'm finally trying to make use of the decoded campaign object like this
class CoopOverviewViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource {
override func viewDidLoad() {
super.viewDidLoad()
//do stuff
// load Campaigns
self.apiService.getCampaignList(completion: {result in
switch result {
case .success(let campaigns):
DispatchQueue.main.async {
print("CAMPAIGN DATA: ", campaigns[0].name)
}
case .failure(let error):
print("An error occured \(error.localizedDescription)")
}
})
...
}
Now I've got 2 questions:
1)
let element: T?
is actually called "campaigns" in the api response for this call. However, it could be cooperations, payments, etc. in other api responses with that same ResponseMultipleElements surrounding structure. Is there a way to make the key swappable here, like I've done with the value with the use of generics? If not, how else would I solve that problem?
2) I'm getting this error:
typeMismatch(Swift.Array<Any>,
Swift.DecodingError.Context(codingPath:
[CodingKeys(stringValue: "detailresponse", intValue: nil)],
debugDescription: "Expected to decode Array<Any> but found a dictionary instead.", underlyingError: nil))
I've told Swift that the "campaigns" part of the detailresponse is an Array of campaign objects - at least that's my understanding when looking at the api response. However, the error seems to say it's a dictionary. First, I don't get why that is and would really like to understand it. Second, I don't know how to tell it that it should expect a dictionary instead of an array then - getting confused with generics here a bit.
Thank you so much for your help in advance!

Answer 1

This is an approach to add a custom key decoding strategy to map any CodingKey but count in detailresponse to fixed value element.
First of all create a custom CodingKey
struct AnyCodingKey: CodingKey {
var stringValue: String
init?(stringValue: String) {
self.stringValue = stringValue
}
var intValue: Int? { return nil }
init?(intValue: Int) {
return nil
}
}
Then create the structs similar to Sh_Khan's answer, in most cases classes are not needed
struct ResponseMultipleElements<T: Decodable>: Decodable {
let statuscode : Int
let response_type : Int
let errormessage : String?
let detailresponse : Element<T>
}
struct Element<U: Decodable>: Decodable {
let count : String
let element : U
}
struct Campaign : Decodable {
let id : Int
let name : String
let targetagegroup : String?
}
Now comes the funny part. Create a custom key decoding strategy which returns always element for the CodingKey in detailresponse which is not count
do {
let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .custom { codingKeys in
let lastKey = codingKeys.last!
if lastKey.intValue != nil || codingKeys.count != 2 { return lastKey }
if lastKey.stringValue == "count" { return lastKey }
return AnyCodingKey(stringValue: "element")!
}
let result = try decoder.decode(ResponseMultipleElements<[Campaign]>.self, from: data)
completion(.success(result.detailresponse.element))
} catch {
print("Error is: ", error)
completion(.failure(error))
}