Swift & Codable: how to "bypass" some JSON levels? - json

Question

I would like to use this Pokémon API to fetch some data and convert it into a Swift Pokemon struct.
Here is an extract of the response I get when fetching Pokemon #142:
{
"id": 142,
"name": "aerodactyl",
"types": [{
"type": {
"name": "rock",
"url": "https://pokeapi.co/api/v2/type/6/"
},
"slot": 1
},
{
"type": {
"name": "flying",
"url": "https://pokeapi.co/api/v2/type/3/"
},
"slot": 2
}
]
}
Here is the struct I wrote to convert this JSON into a Swift type:
struct Pokemon: Codable {
var id: Int
let name: String
var types: [PokemonType]?
}
struct PokemonType: Codable {
var type: PokemonTypeContent
}
struct PokemonTypeContent: Codable {
var name: PokemonTypeNameContent
}
enum PokemonTypeNameContent: String, Codable {
case flying = "flying"
case rock = "rock"
// ...
}
Now here is my problem: when I want to get the Pokemon types, I need to dig into this:
pokemon.types.first?.type.name
I would like to know if I have instead a way of getting the PokemonTypeNameContent array in the Pokemon struct, to do something like this:
struct Pokemon {
var types: [PokemonTypeNameContent]?
}
(I am not interested in getting the slot values).
Thank you for your help!

Answer 1

You can do custom encoding for PokemonTypeNameContent, and traverse through the levels of JSON using nestedContainer
enum PokemonTypeNameContent: String, Decodable {
case flying = "flying"
case rock = "rock"
// ...
enum OuterCodingKeys: CodingKey { case type }
enum InnerCodingKeys: CodingKey { case name }
init(from decoder: Decoder) throws {
// this is the container for each JSON object in the "types" array
let container = try decoder.container(keyedBy: OuterCodingKeys.self)
// this finds the nested container (i.e. JSON object) associated with the key "type"
let innerContainer = try container.nestedContainer(keyedBy: InnerCodingKeys.self, forKey: .type)
// now we can decode "name" as a string
let name = try innerContainer.decode(String.self, forKey: .name)
if let pokemonType = Self.init(rawValue: name) {
self = pokemonType
} else {
throw DecodingError.typeMismatch(
PokemonTypeNameContent.self,
.init(codingPath: innerContainer.codingPath + [InnerCodingKeys.name],
debugDescription: "Unknown pokemon type '\(name)'",
underlyingError: nil
)
)
}
}
}
// Pokemon can then be declared like this:
struct Pokemon: Decodable {
let id: Int
let name: String
let types: [PokemonTypeNameContent]
}
Do note that this means that you lose the option of decoding PokemonTypeNameContent as a regular enum. If you do want to do that, put the custom decoding code into a property wrapper. Note that we would be decoding the entire JSON array, instead of each JSON object.
#propertyWrapper
struct DecodePokemonTypes: Decodable {
var wrappedValue: [PokemonTypeNameContent]
init(wrappedValue: [PokemonTypeNameContent]) {
self.wrappedValue = wrappedValue
}
enum OuterCodingKeys: CodingKey { case type }
enum InnerCodingKeys: CodingKey { case name }
init(from decoder: Decoder) throws {
// container for the "types" JSON array
var unkeyedContainer = try decoder.unkeyedContainer()
wrappedValue = []
// while we are not at the end of the JSON array
while !unkeyedContainer.isAtEnd {
// similar to the first code snippet
let container = try unkeyedContainer.nestedContainer(keyedBy: OuterCodingKeys.self)
let innerContainer = try container.nestedContainer(keyedBy: InnerCodingKeys.self, forKey: .type)
let name = try innerContainer.decode(String.self, forKey: .name)
if let pokemonType = PokemonTypeNameContent(rawValue: name) {
wrappedValue.append(pokemonType)
} else {
throw DecodingError.typeMismatch(
PokemonTypeNameContent.self,
.init(codingPath: innerContainer.codingPath + [InnerCodingKeys.name],
debugDescription: "Unknown pokemon type '\(name)'",
underlyingError: nil
)
)
}
}
}
}
// You would write this in Pokemon
#DecodePokemonTypes
var types: [PokemonTypeNameContent]