Exclude CodingKeys that doesn't need to be altered? - swift

Question

Say I have a struct User model which has many properties in it.
struct User: Codable {
let firstName: String
let lastName: String
// many more properties...
}
As you can see above it conforms to Codable. Imagine if the lastName property is should be encoded/decoded as secondName and I would like to keep it as lastName at my end, I need to add the CodingKeys to the User model.
struct User: Codable {
//...
private enum CodingKeys: String, CodingKey {
case firstName
case lastName = "secondName"
// all the other cases...
}
}
Is there any possible way to avoid including all the cases in CodingKeys that have the same value as rawValue like the firstName in the above example (Feels redundant)? I know if I avoid the cases in CodingKeys it won't be included while decoding/encoding. But, is there a way I could override this behaviour?

Answer 1

There is a codable way, but the benefit is questionable.
Create a generic CodingKey
struct AnyKey: CodingKey {
var stringValue: String
var intValue: Int?
init?(stringValue: String) { self.stringValue = stringValue; self.intValue = nil }
init?(intValue: Int) { self.stringValue = String(intValue); self.intValue = intValue }
}
and add a custom keyDecodingStrategy
struct User: Codable {
let firstName: String
let lastName: String
let age : Int
}
let jsonString = """
{"firstName":"John", "secondName":"Doe", "age": 30}
"""
let data = Data(jsonString.utf8)
do {
let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .custom({ keyPath -> CodingKey in
let key = keyPath.last!
return key.stringValue == "secondName" ? AnyKey(stringValue:"lastName")! : key
})
let result = try decoder.decode(User.self, from: data)
print(result)
} catch {
print(error)
}

Answer 2

There is not such a feature at this time. But you can take advantage of using computed properties and make the original one private.
struct User: Codable {
var firstName: String
private var secondName: String
var lastName: String {
get { secondName }
set { secondName = newValue }
}
}
So no need to manual implementing of CodingKeys at all and it acts exactly like the way you like. Take a look at their counterparts: