How to parse weather data from NASA API - json

Question

So, the issue is - I am trying to display the Mars weather from the Mars Insight API. Here is a link Insight Weather, the data is returning in JSON format and has three levels. The keys have names that change depending on the current date (sols). How to make the structure of mutable properties?... when the property names change every day. Do we have any instruments to parse such JSON?
{
"815": {
"First_UTC": "2021-03-12T14:54:38Z",
"Last_UTC": "2021-03-13T15:34:09Z",
"Month_ordinal": 12,
"Northern_season": "late winter",
"PRE": {
"av": 728.378,
"ct": 153082,
"mn": 708.4211,
"mx": 744.9279
},
"Season": "winter",
"Southern_season": "late summer",
"WD": {
"most_common": null
}
},
"818": {
"First_UTC": "2021-03-15T20:01:49Z",
"Last_UTC": "2021-03-16T17:32:54Z",
"Month_ordinal": 12,
"Northern_season": "late winter",
"PRE": {
"av": 727.696,
"ct": 109855,
"mn": 710.223,
"mx": 743.946
},
"Season": "winter",
"Southern_season": "late summer",
"WD": {
"most_common": null
}
},
"819": {
....
,
"sol_keys": [
"815",
"818",
"819",
"820",
"821"
],
"validity_checks": {
"815": {
"PRE": {
"sol_hours_with_data": [
0,
1,
2,
3,
4,
5,
6,
7,
8,
9,
10,
11,
12,
13,
14,
15,
16,
17,
18,
19,
20,
21,
22,
23
],
"valid": true
}
}
So, Structure:
import Foundation
struct WeatherData: Decodable {
let season: String?
let pre: pre?
let solKeys: [String]
enum CodingKeys: String, CodingKey {
case season = "season"
case pre = "PRE"
case solKeys = "sol_keys"
}
struct pre: Decodable {
let av: Double?
let mn: Double?
let mx: Double?
enum CodingKeys: String, CodingKey {
case av = "av"
case mn = "mn"
case mx = "mx"
}
}
}
Parsing:
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
let urlString = "https://api.nasa.gov/insight_weather/?api_key=DEMO_KEY&feedtype=json&ver=1.0"
guard let url = URL(string: urlString) else { return}
URLSession.shared.dataTask(with: url) { (data, response, error) in
guard let safeData = data else { return }
do {
let solWeather = try JSONDecoder().decode([String:WeatherData].self, from: safeData)
if let keys = solWeather["sol_keys"] {
for key in keys { //error: For-in loop requires 'WeatherData' to conform to 'Sequence'
let report = solWeather [key]
}
}
print(solWeather)
}
catch let error {
print(error)
}
}.resume()
}
}
Got an error: For-in loop requires 'WeatherData' to conform to 'Sequence'
Don't understand why :(( Can someone help me?
Thanks!

Answer 1

You cannot decode [String:WeatherData].self because the dictionary contains other values which are not WeatherData, for example the [String] value of sol_keys.
The only way to decode this JSON with JSONDecoder is to implement init(with decoder, decode the sol_keys and create your own temporary CodingKeys to be able to decode the arbitrary dictionary keys.
First declare the custom CodingKey
public struct SolKeys: CodingKey {
public let stringValue: String
public init?(stringValue: String) { self.stringValue = stringValue }
public var intValue: Int? { return nil }
public init?(intValue: Int) { return nil }
}
The Decodable structs are
struct SolData : Decodable {
let firstUTC, lastUTC : Date
let pre : Pre
private enum CodingKeys : String, CodingKey {
case firstUTC = "First_UTC", lastUTC = "Last_UTC", pre = "PRE"
}
}
struct Pre: Decodable {
let av, mn, mx : Double
}
struct WeatherData: Decodable {
let solKeys: [String]
var soldata = [String:SolData]()
enum CodingKeys: String, CodingKey {
case solKeys = "sol_keys"
}
init(from decoder : Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
self.solKeys = try container.decode([String].self, forKey: .solKeys)
let customContainer = try decoder.container(keyedBy: SolKeys.self)
for key in solKeys {
let solKey = SolKeys(stringValue: key)!
let data = try customContainer.decode(SolData.self, forKey: solKey)
soldata[key] = data
}
}
}
And the code to receive and decode the data
let urlString = "https://api.nasa.gov/insight_weather/?api_key=DEMO_KEY&feedtype=json&ver=1.0"
let url = URL(string: urlString)!
URLSession.shared.dataTask(with: url) { (data, response, error) in
if let error = error { print(error); return }
do {
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .iso8601
let solWeather = try decoder.decode(WeatherData.self, from: data!)
let keys = solWeather.solKeys
for key in keys {
let report = solWeather.soldata[key]!
print(report)
}
}
catch {
print(error)
}
}.resume()