How to handle a mix of standard and customized Swift 4 Decodable properties? - swift4

Question

I've been experimenting with customized Decodable properties for handling JSON in Swift 4 and I'm really impressed with the ease of mapping tricky type and format conversions.
However in the JSON data structures that the server exposes to me, only a handful of properties need this treatment. The rest are simple integers and strings. Is there some way to mix the customized decoder with the standard one?
Here's a simplified example showing what I'd like to get rid of:
struct mystruct : Decodable {
var myBool: Bool
var myDecimal: Decimal
var myDate: Date
var myString: String
var myInt: Int
}
extension mystruct {
private struct JSONsource: Decodable {
var my_Bool: Int
var my_Decimal: String
var my_Date: String
// These seem redundant, how can I remove them?
var myString: String
var myInt: Int
}
private enum CodingKeys: String, CodingKey {
case item
}
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
let item = try container.decode(JSONsource.self, forKey: .item)
myBool = item.my_Bool == 1 ? true : false
myDecimal = Decimal(string: item.my_Decimal)!
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSSSSSZZZZZ"
dateFormatter.locale = Locale(identifier: "en_US_POSIX")
myDate = dateFormatter.date(from: item.my_Date)!
// Can I somehow get rid of this redundant-looking code?
myString = item.myString
myInt = item.myInt
}
}
let myJSON = """
{
"item": {
"my_Decimal": "123.456",
"my_Bool" : 1,
"my_Date" : "2019-02-08T11:14:31.4547774-05:00",
"myInt" : 148727,
"myString" : "Hello there!"
}
}
""".data(using: .utf8)
let x = try JSONDecoder().decode(mystruct.self, from: myJSON!)
print("My decimal: \(x.myDecimal)")
print("My bool: \(x.myBool)")
print("My date: \(x.myDate)")
print("My int: \(x.myInt)")
print("My string: \(x.myString)")

Answer 1

JSONDecoder has a dateDecodingStrategy. No need to decode it manually. To simplify decoding your coding keys you can set decoders property .keyDecodingStrategy to . convertFromSnakeCase. You have also some type mismatches you can handle adding computed properties. Btw this might help creating a custom formatter for your ISO8601 date string with fractional seconds. How to create a date time stamp and format as ISO 8601, RFC 3339, UTC time zone? . Last but not least, it is Swift convention to name your structures using UpperCamelCase
struct Root: Codable {
let item: Item
}
struct Item : Codable {
var myBool: Int
var myDecimal: String
var myDate: Date
var myString: String
var myInt: Int
}
extension Item {
var bool: Bool {
return myBool == 1
}
var decimal: Decimal? {
return Decimal(string: myDecimal)
}
}
extension Item: CustomStringConvertible {
var description: String {
return "Iten(bool: \(bool), decimal: \(decimal ?? 0), date: \(myDate), string: \(myString), int: \(myInt))"
}
}
let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .convertFromSnakeCase
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSSSSSZZZZZ"
dateFormatter.locale = Locale(identifier: "en_US_POSIX")
decoder.dateDecodingStrategy = .formatted(dateFormatter)
do {
let item = try decoder.decode(Root.self, from: myJSON).item
print(item) // Iten(bool: true, decimal: 123.456, date: 2019-02-08 16:14:31 +0000, string: Hello there!, int: 148727)
}
catch {
print(error)
}