Dynamically change API data fetching structure - ios

Question

I am fetching data from an API that keeps changing it's format several times a day from String to Double erratically..
Is it possible to do something to the struct to prevent returning nil when fetching and automatically using with the right type?
struct BitcoinGBP : Decodable {
let price : Double
let percentChange24h : Double
private enum CodingKeys : String, CodingKey {
case price = "PRICE"
case percentChange24h = "CHANGEPCT24HOUR"
}
}
Would simply using Double? work?

Answer 1

Write a custom initializer to handle both cases
struct BitcoinGBP : Decodable {
let price : Double
let percentChange24h : Double
private enum CodingKeys : String, CodingKey {
case price = "PRICE"
case percentChange24h = "CHANGEPCT24HOUR"
}
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
percentChange24h = try container.decode(Double.self, forKey: .percentChange24h)
do {
price = try container.decode(Double.self, forKey: .price)
} catch DecodingError.typeMismatch(_, _) {
let stringValue = try container.decode(String.self, forKey: .price)
price = Double(stringValue)!
}
}
}

Answer 2

In my experience you need to design your structures, models to correspond to what you expect to use in your application and not what API will give you. You need to be prepared for the API to give you incorrect data types or missing, strange data.
If API changes too much then users will need to update but this is generally never done. Endpoints must have versions and need to change version when a big difference is made. If this is not the case that it is flawed API (these things still do happen) in which case you should use your own server, proxy which connects to desired server and modifies their API to your own. You put some tests on it to detect if their API has changed and modify your own as quickly as possible so all applications can still connect to it. But this is way out of the scope of this question.
If your structure must be with having price and percentage change in 24h where both are double then simply expect string or anything from the API. I like to avoid any tools that do that automatically so I just use convenience constructors and a set of tools of my own to produce something like:
class BitcoinGBP {
var price: Double = 0.0
var priceChange24h: Double = 0.0
convenience init(price: Double, priceChange24h: Double) {
self.init()
self.price = price
self.priceChange24h = priceChange24h
}
/// Construuctor designed to accept JSON formated dictionary
///
/// - Parameter descriptor: A JSON descriptor
convenience init(descriptor: [String: Any]) {
self.init()
self.price = double(value: descriptor["PRICE"]) ?? 0.0
self.priceChange24h = double(value: descriptor["CHANGEPCT24HOUR"]) ?? 0.0
}
/// A conveninece method to extract a double value
///
/// - Parameter value: A value to be converted
/// - Returns: Double value if possible
func double(value: Any?) -> Double? {
if let value = value as? String {
return Double(value)
} else if let value = value as? Double {
return value
} else if let value = value as? Float {
return Double(value)
} else if let value = value as? Int {
return Double(value)
} else if let value = value as? Bool {
return value ? 1.0 : 0.0
} else {
return nil
}
}
}
Now the rest is just depending on what functionality you need.