How to decode this particular JSON model? - ios

Question

EDIT 2:
After changing the Model struct and calling the JSON decoder without a completion handler, I have managed to get this to work. Thank you all for your help.
Fixed code:
Model
import Foundation
struct RatesResponse: Decodable, Hashable{
let rates: [String: Double]
}
Decoder Class
import Foundation
class RatesModelData{
public var rateCurrency = [String]()
public var rateValue = [Double]()
public func getRates(currency: String){
guard let url = URL(string: "https://api.exchangerate.host/latest?base=\(currency)")
else {
print("URL is invalid")
return
}
var request = URLRequest(url: url)
let dataTask = URLSession.shared.dataTask(with: request){data, response, error in
if let data = data {
do{
let ratesResponse = try JSONDecoder().decode(RatesResponse.self, from: data)
for rate in ratesResponse.rates{
self.rateCurrency.append(rate.key)
self.rateValue.append(rate.value)
}
print(self.rateCurrency)
} catch {
print(error)
}
}
}
dataTask.resume()
}
}
EDIT:
I have changed let rate = Rates to let rates = Rates, modified the decoder class to the following and added a do/catch statement however I am now getting the error "The data given is invalid JSON". I have updated the code snippets as well.
I have this json model:
https://api.exchangerate.host/latest?base=usd
and I cannot for the life of me figure out how to decode it properly. I know its a dictionary and has to be decoded as such but i'm struggling to wrap my head around what i'm doing wrong.
Model:
struct RatesResponse: Decodable, Hashable{
let rates : Rates
}
struct Rates: Decodable, Hashable {
let rates: [String: Double]
}
Decoder Class:
class RatesModelData{
public func getRates(currency: String, _ completionHandler: #escaping(Rates) -> Void){
guard let url = URL(string: "https://api.exchangerate.host/latest?base=\(currency)")
else {
print("URL is invalid")
return
}
var request = URLRequest(url: url)
request.httpMethod = "GET"
request.setValue("application/json", forHTTPHeaderField: "ACCEPT")
let dataTask = URLSession.shared.dataTask(with: request){data, response, error in
do{
if let data = data {
if let ratesResponse = try JSONDecoder().decode(RatesResponse?.self, from: data){
completionHandler(ratesResponse.rates)
}
return
}
guard let httpResponse = response as? HTTPURLResponse, (200...299).contains(httpResponse.statusCode) else{
print("Error with response: \(response)")
return
}
if let error = error {
print("Error Thrown : \(error)")
return
}
} catch {
print(error)
}
}
dataTask.resume()
}
}
I ideally want to get this to be displayed in a list view (SwiftUI), but for now just asking for some advice as to where i've gone wrong with my decoding.

Answer 1

Your object model suggests that the value associated with rates key is another object with another rates key. But that doesn’t match the JSON you have provided. The value associated with top-level rates key is just a dictionary.
So you could do the following and be done with it:
struct ResponseObject: Decodable {
let rates: [String: Double]
}
Or, if you want to capture everything in this JSON, you could add the additional properties:
struct Motd: Decodable {
let msg: String
let url: URL
}
struct ResponseObject: Decodable {
let motd: Motd
let success: Bool
let base: String
let date: Date
let rates: [String: Double]
}
And then:
do {
let formatter = DateFormatter()
formatter.locale = Locale(identifier: "en_US_POSIX")
formatter.dateFormat = "yyyy-MM-dd"
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .formatted(formatter)
let responseObject = try decoder.decode(ResponseObject.self, from: data)
print(responseObject)
} catch {
print(error)
}
FWIW, the base, date, and rates objects likely could/should be optionals, e.g.:
struct ResponseObject: Decodable {
let motd: Motd
let success: Bool
let base: String?
let date: Date?
let rates: [String: Double]?
}
To confirm, we would need to see what a well-formed non-success response looks like. Glancing at the documentation it was not immediately obvious, but something like the above is likely what you want, where JSONDecoder would be able to successfully decode both success responses and failure responses.

Answer 2

I went through the struggles of parsing JSON into structs last year so I feel comfortable helping you out. It's definitely a challenging concept to wrap your head around:
First, let me explain what's wrong with your structs:
struct RatesResponse: Decodable, Hashable{
let rates : Rates
// "rates" is a root-level key in your JSON.
// You're giving it the value of your structure Rates,
// which also has a key titled "rates".
}
struct Rates: Decodable, Hashable {
let rates: [String: Double]
}
Here's what your JSON would look like if these structs could be used to parse it:
{
"rates": {
"rates": {
"AED": 3.671827,
"AFN": 80.098152
}
}
In your actual JSON, your "rates" key has the value of an object (or dictionary, which is nothing more than an array with keys and values) I'm sure you don't want to make a struct with a variable for every single currency, so just use an array in your struct, with an element type of String: Double
struct RatesResponse: Decodable, Hashable{
let rates : [String: Double]
}
JSON key "rates" has a value of a dictionary where the keys are strings and the values are doubles.
After decoding in your URLSession, you can do:
for rate in ratesResponse.rates {
let currency = rate.key // AED, AFN, etc.
let exchangeRate = rate.value // 3.671827, 80.098152, etc.
// With these variables, you can append each of them to a new, separate array for use in your SwiftUI list.
}