How to use a value from a struct dictionary and convert it to another type? - swift

Question

Here I want to be able to use the value returned from an array. It returns as a type from a struct. I'm unsure of how to use the value as an integer.
struct Item: Codable {
let data: [String : Datum]
}
struct Datum: Codable {
let value: Int
}
var array = Item(data: ["1" : Datum(value: 1),"2": Datum(value: 2), "3":Datum(value: 3)])
var keyArray = ["1", "2", "3"]
print(array.data[keyArray[0]]!)
// Prints Datum(value: 1)
print(array.data[keyArray[0]]! + 1)
//This produces an error "Cannot convert value of type 'Datum' to expected argument type 'Int'"
//Expected result should be 2
My use case is when I get returned a decoded JSON it normally comes back as a dictionary. I'm wanting to use the values returned with a key but I feel like I'm one step short.
Context
Full JSON Link
I'm going to retrieve values from this JSON. (Example from large JSON file)
{"data":{"2":{"high":179,"highTime":1628182107,"low":177,"lowTime":1628182102},"6":{"high":189987,"highTime":1628179815,"low":184107,"lowTime":1628182100},"8":{"high":190800,"highTime":1628181435,"low":188100,"lowTime":1628182095}
}}
The string in front refers to an item ID.
The struct that I came up to decode goes like this.
// MARK: - Single
struct Single: Codable {
let data: [String: Datum]
}
// MARK: - Datum
struct Datum: Codable {
let high, highTime: Int
let low, lowTime: Int?
}
From there I'm planning to iterate through the JSON response to retrieve the item prices I'd want.
#available(iOS 15.0, *)
struct ContentView: View {
#State var dataFromURL: Single = Single(data: [:])
var body: some View {
VStack {
Text("Hello, world!")
.padding()
}
.onAppear {
async {
try await decode()
}
}
}
func decode() async throws -> Single {
let decoder = JSONDecoder()
let urlString = "https://prices.runescape.wiki/api/v1/osrs/latest"
guard let url = URL(string: urlString) else { throw APIError.invalidURL }
let (data, response) = try await URLSession.shared.data(from: url)
guard let response = response as? HTTPURLResponse, response.statusCode == 200 else { throw APIError.invalidServerResponse }
guard let result = try? decoder.decode(Single.self, from: data) else { throw APIError.invalidData }
//We copy our result to an existing variable
dataFromURL = result
return result
}
}
enum APIError: Error {
case invalidURL
case invalidServerResponse
case invalidData
}
extension APIError: CustomStringConvertible {
public var description: String {
switch self {
case.invalidURL:
return "Bad URL"
case .invalidServerResponse:
return "The server did not return 200"
case .invalidData:
return "Their server returned bad data"
}
}
}
I haven't gotten further than grabbing the response from the URL. That is why once I start manipulating the data I'd like to use the response to find other things like what would a profit/loss with another item become. Which isn't the goal of this question at the moment.

Answer 1

The object model to parse that JSON would be:
struct Price: Decodable {
let high: Int?
let highTime: Date?
let low: Int?
let lowTime: Date?
}
struct ResponseObject: Decodable {
let prices: [String: Price]
enum CodingKeys: String, CodingKey {
case prices = "data"
}
}
(Note, the documentation says that either high or low might be missing, so we have to make them all optionals.)
Now, the id number is being passed as a string in the JSON/ResponseObject. But that is a number (look at mapping). So, I would remap that dictionary so that the key was an integer, e.g.
enum ApiError: Error {
case unknownError(Data?, URLResponse?)
}
func fetchLatestPrices(completion: #escaping (Result<[Int: Price], Error>) -> Void) {
let url = URL(string: "https://prices.runescape.wiki/api/v1/osrs/latest")!
let task = URLSession.shared.dataTask(with: url) { data, response, error in
guard
error == nil,
let responseData = data,
let httpResponse = response as? HTTPURLResponse,
200..<300 ~= httpResponse.statusCode
else {
completion(.failure(error ?? ApiError.unknownError(data, response)))
return
}
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .secondsSince1970
do {
let responseObject = try decoder.decode(ResponseObject.self, from: responseData)
let keysAndValues = responseObject.prices.map { (Int($0.key)!, $0.value) }
let prices = Dictionary(uniqueKeysWithValues: keysAndValues)
completion(.success(prices))
} catch {
completion(.failure(error))
}
}
task.resume()
}
The code that converts that [String: Price] to a [Int: Price] is this:
let keysAndValues = responseObject.prices.map { (Int($0.key)!, $0.value) }
let prices = Dictionary(uniqueKeysWithValues: keysAndValues)
I must say that this is a questionable API design, to have keys returned as integers in one endpoint and as strings as another. But it is what it is. So, the above is how you handle that.
Anyway, now that you have a dictionary of prices, keyed by the id numbers, you can use that in your code, e.g.
var prices: [Int: Price] = [:]
var products: [Product] = []
let group = DispatchGroup()
group.enter()
fetchLatestPrices { result in
defer { group.leave() }
switch result {
case .failure(let error):
print(error)
case .success(let values):
prices = values
}
}
group.enter()
fetchProducts { result in
defer { group.leave() }
switch result {
case .failure(let error):
print(error)
case .success(let values):
products = values }
}
group.notify(queue: .main) {
for product in products {
print(product.name, prices[product.id] ?? "no price found")
}
}
Where
func fetchProducts(completion: #escaping (Result<[Product], Error>) -> Void) {
let url = URL(string: "https://prices.runescape.wiki/api/v1/osrs/mapping")!
let task = URLSession.shared.dataTask(with: url) { data, response, error in
guard
error == nil,
let responseData = data,
let httpResponse = response as? HTTPURLResponse,
200..<300 ~= httpResponse.statusCode
else {
completion(.failure(error ?? ApiError.unknownError(data, response)))
return
}
do {
let products = try JSONDecoder().decode([Product].self, from: responseData)
completion(.success(products))
} catch {
completion(.failure(error))
}
}
task.resume()
}
And
struct Product: Decodable {
let id: Int
let name: String
let examine: String
let members: Bool
let lowalch: Int?
let limit: Int?
let value: Int
let highalch: Int?
let icon: String
}
(As an aside, I do not know if some of these other properties should be optionals or not. I just used optionals where I empirically discovered that they are occasionally missing.)