Codable decoding values in JSON converting snake case to camel - json

Question

When using Swift Codable you can specify a keyDecodingStrategy that will convert snake_case to camelCase. This works great for keys in a dictionary, but is there any solution for decoding values in a dictionary in a similarly clean way?
I have an enumeration that is used as a key in one place and as a value in another:
enum Foo: String, Codable, CodingKey, CaseIterable {
case bar
case bazQux // baz_qux in JSON, say
}
Then this is used as a key like so:
struct MyStruct: Codable {
enum Keys: String, CodingKey {
case myKey
}
let myProperty: [Bool]
public init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: Foo.self)
myProperty = Foo.allCases.map {
try container.decode(Bool.self, forKey: $0)
}
}
}
But it is also used as a value like so:
struct Buz: Decodable {
enum CodingKeys: String, CodingKey {
case foo
}
// Note this is called using a decoder with keyDecodingStrategy = .convertFromSnakeCase
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
let foo = try container.decode(Foo.self, forKey: .foo)
}
}
The JSON for example might include a line like this:
"foo": "baz_qux"
The value decoding only works if I set the raw value of the bazQux case to be baz_qux. But then that breaks the key decoding. It would also be annoying to have to make two separate enums for the same thing just to avoid this problem.
So I can then initialize the right model corresponding to the value.
I'd also like to avoid employing a "hacky" solution… Is there something reasonably elegant that works well with Codable?

Answer 1

Wound up adding a custom decoding initializer on Foo:
public init(from decoder: Decoder) throws {
let rawValue = try decoder.singleValueContainer().decode(String.self)
if let foo = Self.init(rawValue: rawValue.snakeToCamelCase) {
self = foo
} else {
throw CodingError.unknownValue
}
}
snakeToCamelCase is a simple extension method on String I added locally. Plus need to add the enum CodingError: Error to Foo if you want some error handling.
This isn't ideal but at least it's not too complicated. I would rather rely on built-in case conversion methods but I don't see a way to do that here.