Why JSONDecoder doesn't work with a date format? - json

Question

I have a simple structs to represent a JSON about a stock:
struct Share: Decodable {
enum CodingKeys: String, CodingKey {
case metaData = "Meta Data"
case prices = "Time Series (Daily)"
}
var metaData: [String: String]
var prices: [Date: TradingDay]
}
struct TradingDay: Decodable {
enum CodingKeys: String, CodingKey {
case open = "1. open"
case close = "4. close"
case high = "2. high"
case low = "3. low"
}
enum DecodingErrors: Error {
case canNotMakeDouble
case invalidCodingKeys
}
var open: Double
var close: Double
var high: Double
var low: Double
init(from decoder: Decoder) throws {
guard let container = try? decoder.container(keyedBy: CodingKeys.self) else {
throw DecodingErrors.invalidCodingKeys
}
guard let open = try? Double(container.decode(String.self, forKey: .open)),
let close = try? Double(container.decode(String.self, forKey: .close)),
let high = try? Double(container.decode(String.self, forKey: .high)),
let low = try? Double(container.decode(String.self, forKey: .low)) else {
throw DecodingErrors.canNotMakeDouble
}
self.open = open
self.close = close
self.high = high
self.low = low
}
}
JSON looks like this:
{
"Meta Data": {
"1. Information": "Daily Prices (open, high, low, close) and Volumes",
"2. Symbol": "IBM",
"3. Last Refreshed": "2022-07-01",
"4. Output Size": "Compact",
"5. Time Zone": "US/Eastern"
},
"Time Series (Daily)": {
"2022-07-01": {
"1. open": "141.0000",
"2. high": "141.6700",
"3. low": "139.2600",
"4. close": "141.1200",
"5. volume": "4012106"
},
"2022-06-30": {
"1. open": "139.5800",
"2. high": "142.4600",
"3. low": "139.2800",
"4. close": "141.1900",
"5. volume": "4878020"
},
and so on.
I'm trying to decode this with the following code:
if let (data, _) = try? await URLSession.shared.data(for: request) {
let decoder = JSONDecoder()
let formatter = DateFormatter()
formatter.dateFormat = "yyyy-MM-dd"
decoder.dateDecodingStrategy = .formatted(formatter)
do {
let share = try decoder.decode(Share.self, from: data)
print(share.metaData)
print(share.prices)
} catch {
print(error.localizedDescription)
}
}
But all I see is just an error.
When I make a prices dictionary (7th row) [String: TradingDay] type, it works appropriately.
Why doesn't it decode the dates, though I passed in the date format?
Thanks everyone.