Convert string to Date/Int/Double using codable

Question

I am getting a response from an API but the problem is that the API is sending values back as a string of dates and doubles. I am therefore getting the error "Expected to decode Double but found a string/data instead." I have structured my struct like this to solve the problem but this seems like a patch. Is there any better way to fix this issue? I feel like apple has thought of this and included something natively to address this.

struct SimpleOrder:Codable{ 
    var createdDate:Date! {
        return createdDateString.dateFromISO8601
    }
    var createdDateString:String

    var orderId:String!

    var priceVal:Double!
    var priceString:String{
        didSet {
            priceVal = Double(self.priceString)!
        }
    }

    private enum CodingKeys: String, CodingKey {
        //case createdDate
        case createdDateString = "time"

        case orderId = "id"

        case priceVal
        case priceString = "price"
    }
}

I don't know if this is relevant but this is how it is being used. I am getting the data as a string and converting it to data which is stored in the dataFromString variable

let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .iso8601 //This is irrelevant though because the date is returned as a string. 

do{
    let beer = try decoder.decode(SimpleOrder.self, from: dataFromString)
    print ("beer is \(beer)")
}catch let error{
    print ("error is \(error)")
}

As a result of using codable, I am getting an error when trying to get an empty instance of SimpleOrder. Before I was using codable, I had no issues using SimpleOrder() without any arguments.

Error: Cannot invoke initializer for type 'SimpleOrder' with no arguments

var singlePoint = SimpleOrder()

Don't use didset. Make priceVal a computed property with a getter but without a setter — Leo Dabus, Dec 01 '17 at 20:00
so that is the method that I used for the date. There is no better way to do it? Nothing that is build into Codable so that there doesn't need to be two duplicate properties in the struct (one as a string and the other as a date/double/int). — Nevin Jethmalani, Dec 01 '17 at 20:02
Btw no need to repeat case case case. Just use a single one `case createdDateString = "time", orderId = "id", priceString = "price"` — Leo Dabus, Dec 01 '17 at 20:03
You are not storing any value. It will be computed when needed — Leo Dabus, Dec 01 '17 at 20:04
yes I know but I just like the way it looks when there are multiple cases — Nevin Jethmalani, Dec 01 '17 at 20:04
Btw you can add those computed properties in an extension to make your structure more readable — Leo Dabus, Dec 01 '17 at 20:05
awesome thanks a lot! I am also getting this error: `Cannot invoke initializer for type 'SimpleOrder' with no arguments` when I do this `var emptyPoint = SimpleOrder()`. Before I started using codable, this was not an issue. — Nevin Jethmalani, Dec 01 '17 at 20:06
if I don't put priceVal in the keys, then it says it doesn't conform to the codable protocol — Nevin Jethmalani, Dec 01 '17 at 20:07
It won't complain once you make it a read only computed property as I suggested — Leo Dabus, Dec 01 '17 at 20:08
yes, that is why `createdDate ` is commented out above as well — Nevin Jethmalani, Dec 01 '17 at 20:08
For the date you can use a custom date formatter to decode it — Leo Dabus, Dec 01 '17 at 20:09
`decoder.dateDecodingStrategy = .formatted(Formatter.iso8601)` https://stackoverflow.com/questions/28016578/swift-how-to-create-a-date-time-stamp-and-format-as-iso-8601-rfc-3339-utc-tim/28016692#28016692 — Leo Dabus, Dec 01 '17 at 20:11
YES. That is what I was looking for I think for the date. I haven't tried it but it looks like it will work. Do you know how I can have an empty property instance of SimpleOrder? like `let tempOrder = SimpleOrder()` I am getting this error: `Cannot invoke initializer for type 'SimpleOrder' with no arguments` — Nevin Jethmalani, Dec 01 '17 at 20:13
Why would you need that? and Yes you need to create the initializer and make your properties optionals or give them a default value — Leo Dabus, Dec 01 '17 at 20:20
So that I can use that struct like this `var singlePoint = SimpleOrder()` I am not sure if that is what I need. — Nevin Jethmalani, Dec 01 '17 at 20:21
I did that but it is still giving the same issue and it says this is what my argument needs to be `SimpleOrder(from: <#T##Decoder#>)` — Nevin Jethmalani, Dec 01 '17 at 20:25
Again create an initializer providing default values to the properties or nil — Leo Dabus, Dec 01 '17 at 20:26
sorry, how exactly would I do that? `init(){createdDateString=""}` something like this? — Nevin Jethmalani, Dec 01 '17 at 20:30

Leo Dabus · Accepted Answer · 2017-12-01T21:33:40.460

struct SimpleOrder: Codable {
    var created: Date?
    var orderId: String?
    var price: String?
    private enum CodingKeys: String, CodingKey {
        case created = "time", orderId = "id", price
    }
    init(created: Date? = nil, orderId: String? = nil, price: String? = nil) {
        self.created = created
        self.orderId = orderId
        self.price = price
    }
}

extension SimpleOrder {
    var priceValue: Double? {
        guard let price = price else { return nil }
        return Double(price)
    }
}

extension Formatter {
    static let iso8601: DateFormatter = {
        let formatter = DateFormatter()
        formatter.calendar = Calendar(identifier: .iso8601)
        formatter.locale = Locale(identifier: "en_US_POSIX")
        formatter.timeZone = TimeZone(secondsFromGMT: 0)
        formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSXXXXX"
        return formatter
    }()
}

Decoding the json data returned by the API:

let jsonData = Data("""
{
    "time": "2017-12-01T20:41:48.700Z",
    "id": "0001",
    "price": "9.99"
}
""".utf8)

let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .formatted(Formatter.iso8601)

do {
    let simpleOrder = try decoder.decode(SimpleOrder.self, from: jsonData)
    print(simpleOrder)
} catch {
    print(error)
}

Or initialising a new object with no values:

var order = SimpleOrder()

In swift 4: `decoder.dateDecodingStrategy = .iso8601` – jumper Mar 15 '19 at 10:01 — jumper, Mar 15 '19 at 10:01
@jumper that won’t include fractional seconds – Leo Dabus Jun 13 '19 at 13:02 — Leo Dabus, Jun 13 '19 at 13:02

Convert string to Date/Int/Double using codable

1 Answers1