Related
I have a custom struct I want to store in AppStorage:
struct Budget: Codable, RawRepresentable {
enum CodingKeys: String, CodingKey {
case total, spent
}
var total: Double
var spent: Double
init(total: Double = 5000.0, spent: Double = 3000.0) {
self.total = total
self.spent = spent
}
init?(rawValue: String) {
guard let data = rawValue.data(using: .utf8),
let result = try? JSONDecoder().decode(Budget.self, from: data)
else { return nil }
self = result
}
var rawValue: String {
guard let data = try? JSONEncoder().encode(self),
let result = String(data: data, encoding: .utf8)
else {
return ""
}
return result
}
}
I then have the following view:
struct DemoView: View {
#AppStorage(UserDefaults.StorageKeys.budget.rawValue) var budget = Budget()
var body: some View {
Button("Update") {
budget.total = 10
}
}
}
When I tap the button the app crashes with Thread 1: EXC_BAD_ACCESS on guard let data = try? JSONEncoder().encode(self) for rawValue in Budget. What am I doing wrong here?
You are running into infinite recursion. This is because types that conforms to both Encodable and RawRepresentable automatically get this encode(to:) implementation (source), which encodes the raw value. This means that when you call JSONEncoder().encode, it would try to call the getter of rawValue, which calls JSONEncoder().encode, forming infinite recursion.
To solve this, you can implement encode(to:) explicitly:
func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: CodingKeys.self)
try container.encode(total, forKey: .total)
try container.encode(spent, forKey: .spent)
}
Note that you should also implement init(from:) explicitly, because you also get a init(from:) implementation (source) that tries to decode your JSON as a single JSON string, which you certainly do not want.
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
total = try container.decode(Double.self, forKey: .total)
spent = try container.decode(Double.self, forKey: .spent)
}
Here is the code I am using,
struct CreatePostResponseModel : Codable{
var transcodeId:String?
var id:String = ""
enum TopLevelCodingKeys: String, CodingKey {
case _transcode = "_transcode"
case _transcoder = "_transcoder"
}
enum CodingKeys:String, CodingKey{
case id = "_id"
}
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: TopLevelCodingKeys.self)
if let transcodeId = try container.decodeIfPresent(String.self, forKey: ._transcode) {
self.transcodeId = transcodeId
}else if let transcodeId = try container.decodeIfPresent(String.self, forKey: ._transcoder) {
self.transcodeId = transcodeId
}
}
}
Here, transcodeId is decided by either _transcode or _transcoder.
But I want id and rest of the keys (not included here) to be automatically decoded. How can I do it ?
You need to manually parse all the keys once you implement init(from:) in the Codable type.
struct CreatePostResponseModel: Decodable {
var transcodeId: String?
var id: String
enum CodingKeys:String, CodingKey{
case id, transcode, transcoder
}
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
id = try container.decodeIfPresent(String.self, forKey: .id) ?? ""
if let transcodeId = try container.decodeIfPresent(String.self, forKey: .transcode) {
self.transcodeId = transcodeId
} else if let transcodeId = try container.decodeIfPresent(String.self, forKey: .transcoder) {
self.transcodeId = transcodeId
}
}
}
In the above code,
In case you only want to decode the JSON, there is no need to use Codable. Using Decodable is enough.
Using multiple enums for CodingKey seems unnecessary here. You can use a single enum CodingKeys.
If the property name and the key name is an exact match, there is no need to explicitly specify the rawValue of that case in enum CodingKeys. So, there is no requirement of "_transcode" and "_transcoder" rawValues in TopLevelCodingKeys.
Apart from all that, you can use keyDecodingStrategy as .convertFromSnakeCase to handle underscore notation (snake case notation), i.e.
do {
let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .convertFromSnakeCase //here.....
let model = try decoder.decode(CreatePostResponseModel.self, from: data)
print(model)
} catch {
print(error)
}
So, you don't need to explicitly handle all the snake-case keys. It'll be handled by the JSONDecoder on its own.
This can be one of the good solution for you wherever you want you can add multiple keys for one variable:
var transcodeId:String?
public init(from decoder: Decoder) throws {
do {
let container = try decoder.container(keyedBy: CodingKeys.self)
transcodeId = container.getValueFromAvailableKey(codingKeys: [CodingKeys._transcoder,CodingKeys._transcode])
} catch {
print("Error reading config file: \(error.localizedDescription)")
}
}
extension KeyedDecodingContainerProtocol{
func getValueFromAvailableKey(codingKeys:[CodingKey])-> String?{
for key in codingKeys{
for keyPath in self.allKeys{
if key.stringValue == keyPath.stringValue{
do{
return try self.decodeIfPresent(String.self, forKey: keyPath)
} catch {
return nil
}
}
}
}
return nil
}
}
Hope it helps.
The compiler-generated init(from:) is all-or-nothing. You can’t have it decode some keys and “manually” decode others.
One way to use the compiler-generated init(from:) is by giving your struct both of the possible encoded properties, and make transcodeId a computed property:
struct CreatePostResponseModel: Codable {
var transcodeId: String? {
get { _transcode ?? _transcoder }
set { _transcode = newValue; _transcoder = nil }
}
var _transcode: String? = nil
var _transcoder: String? = nil
var id: String = “”
// other properties
}
Swift 4 added the new Codable protocol. When I use JSONDecoder it seems to require all the non-optional properties of my Codable class to have keys in the JSON or it throws an error.
Making every property of my class optional seems like an unnecessary hassle since what I really want is to use the value in the json or a default value. (I don't want the property to be nil.)
Is there a way to do this?
class MyCodable: Codable {
var name: String = "Default Appleseed"
}
func load(input: String) {
do {
if let data = input.data(using: .utf8) {
let result = try JSONDecoder().decode(MyCodable.self, from: data)
print("name: \(result.name)")
}
} catch {
print("error: \(error)")
// `Error message: "Key not found when expecting non-optional type
// String for coding key \"name\""`
}
}
let goodInput = "{\"name\": \"Jonny Appleseed\" }"
let badInput = "{}"
load(input: goodInput) // works, `name` is Jonny Applessed
load(input: badInput) // breaks, `name` required since property is non-optional
You can implement the init(from decoder: Decoder) method in your type instead of using the default implementation:
class MyCodable: Codable {
var name: String = "Default Appleseed"
required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
if let name = try container.decodeIfPresent(String.self, forKey: .name) {
self.name = name
}
}
}
You can also make name a constant property (if you want to):
class MyCodable: Codable {
let name: String
required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
if let name = try container.decodeIfPresent(String.self, forKey: .name) {
self.name = name
} else {
self.name = "Default Appleseed"
}
}
}
or
required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
self.name = try container.decodeIfPresent(String.self, forKey: .name) ?? "Default Appleseed"
}
Re your comment: With a custom extension
extension KeyedDecodingContainer {
func decodeWrapper<T>(key: K, defaultValue: T) throws -> T
where T : Decodable {
return try decodeIfPresent(T.self, forKey: key) ?? defaultValue
}
}
you could implement the init method as
required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
self.name = try container.decodeWrapper(key: .name, defaultValue: "Default Appleseed")
}
but that is not much shorter than
self.name = try container.decodeIfPresent(String.self, forKey: .name) ?? "Default Appleseed"
You can use a computed property that defaults to the desired value if the JSON key is not found.
class MyCodable: Decodable {
var name: String { return _name ?? "Default Appleseed" }
var age: Int?
// this is the property that gets actually decoded/encoded
private var _name: String?
enum CodingKeys: String, CodingKey {
case _name = "name"
case age
}
}
If you want to have the property read-write, you can also implement the setter:
var name: String {
get { _name ?? "Default Appleseed" }
set { _name = newValue }
}
This adds a little extra verbosity as you'll need to declare another property, and will require adding the CodingKeys enum (if not already there). The advantage is that you don't need to write custom decoding/encoding code, which can become tedious at some point.
Note that this solution only works if the value for the JSON key either holds a string or is not present. If the JSON might have the value under another form (e.g. it's an int), then you can try this solution.
Approach that I prefer is using so called DTOs - data transfer object.
It is a struct, that conforms to Codable and represents the desired object.
struct MyClassDTO: Codable {
let items: [String]?
let otherVar: Int?
}
Then you simply init the object that you want to use in the app with that DTO.
class MyClass {
let items: [String]
var otherVar = 3
init(_ dto: MyClassDTO) {
items = dto.items ?? [String]()
otherVar = dto.otherVar ?? 3
}
var dto: MyClassDTO {
return MyClassDTO(items: items, otherVar: otherVar)
}
}
This approach is also good since you can rename and change final object however you wish to.
It is clear and requires less code than manual decoding.
Moreover, with this approach you can separate networking layer from other app.
You can implement.
struct Source : Codable {
let id : String?
let name : String?
enum CodingKeys: String, CodingKey {
case id = "id"
case name = "name"
}
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
id = try values.decodeIfPresent(String.self, forKey: .id) ?? ""
name = try values.decodeIfPresent(String.self, forKey: .name)
}
}
I came across this question looking for the exact same thing. The answers I found were not very satisfying even though I was afraid that the solutions here would be the only option.
In my case, creating a custom decoder would require a ton of boilerplate that would be hard to maintain so I kept searching for other answers.
I ran into this article that shows an interesting way to overcome this in simple cases using a #propertyWrapper. The most important thing for me, was that it was reusable and required minimal refactoring of existing code.
The article assumes a case where you'd want a missing boolean property to default to false without failing but also shows other different variants.
You can read it in more detail but I'll show what I did for my use case.
In my case, I had an array that I wanted to be initialized as empty if the key was missing.
So, I declared the following #propertyWrapper and additional extensions:
#propertyWrapper
struct DefaultEmptyArray<T:Codable> {
var wrappedValue: [T] = []
}
//codable extension to encode/decode the wrapped value
extension DefaultEmptyArray: Codable {
func encode(to encoder: Encoder) throws {
try wrappedValue.encode(to: encoder)
}
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
wrappedValue = try container.decode([T].self)
}
}
extension KeyedDecodingContainer {
func decode<T:Decodable>(_ type: DefaultEmptyArray<T>.Type,
forKey key: Key) throws -> DefaultEmptyArray<T> {
try decodeIfPresent(type, forKey: key) ?? .init()
}
}
The advantage of this method is that you can easily overcome the issue in existing code by simply adding the #propertyWrapper to the property. In my case:
#DefaultEmptyArray var items: [String] = []
Hope this helps someone dealing with the same issue.
UPDATE:
After posting this answer while continuing to look into the matter I found this other article but most importantly the respective library that contains some common easy to use #propertyWrappers for these kind of cases:
https://github.com/marksands/BetterCodable
If you don't want to implement your encoding and decoding methods, there is somewhat dirty solution around default values.
You can declare your new field as implicitly unwrapped optional and check if it's nil after decoding and set a default value.
I tested this only with PropertyListEncoder, but I think JSONDecoder works the same way.
If you think that writing your own version of init(from decoder: Decoder) is overwhelming, I would advice you to implement a method which will check the input before sending it to decoder. That way you'll have a place where you can check for fields absence and set your own default values.
For example:
final class CodableModel: Codable
{
static func customDecode(_ obj: [String: Any]) -> CodableModel?
{
var validatedDict = obj
let someField = validatedDict[CodingKeys.someField.stringValue] ?? false
validatedDict[CodingKeys.someField.stringValue] = someField
guard
let data = try? JSONSerialization.data(withJSONObject: validatedDict, options: .prettyPrinted),
let model = try? CodableModel.decoder.decode(CodableModel.self, from: data) else {
return nil
}
return model
}
//your coding keys, properties, etc.
}
And in order to init an object from json, instead of:
do {
let data = try JSONSerialization.data(withJSONObject: json, options: .prettyPrinted)
let model = try CodableModel.decoder.decode(CodableModel.self, from: data)
} catch {
assertionFailure(error.localizedDescription)
}
Init will look like this:
if let vuvVideoFile = PublicVideoFile.customDecode($0) {
videos.append(vuvVideoFile)
}
In this particular situation I prefer to deal with optionals but if you have a different opinion, you can make your customDecode(:) method throwable
enum PostType: Decodable {
init(from decoder: Decoder) throws {
// What do i put here?
}
case Image
enum CodingKeys: String, CodingKey {
case image
}
}
What do i put to complete this?
Also, lets say i changed the case to this:
case image(value: Int)
How do I make this conform to Decodable?
Here is my full code (which does not work)
let jsonData = """
{
"count": 4
}
""".data(using: .utf8)!
do {
let decoder = JSONDecoder()
let response = try decoder.decode(PostType.self, from: jsonData)
print(response)
} catch {
print(error)
}
}
}
enum PostType: Int, Codable {
case count = 4
}
Also, how will it handle an enum like this?
enum PostType: Decodable {
case count(number: Int)
}
It's pretty easy, just use String or Int raw values which are implicitly assigned.
enum PostType: Int, Codable {
case image, blob
}
image is encoded to 0 and blob to 1
Or
enum PostType: String, Codable {
case image, blob
}
image is encoded to "image" and blob to "blob"
This is a simple example how to use it:
enum PostType : Int, Codable {
case count = 4
}
struct Post : Codable {
var type : PostType
}
let jsonString = "{\"type\": 4}"
let jsonData = Data(jsonString.utf8)
do {
let decoded = try JSONDecoder().decode(Post.self, from: jsonData)
print("decoded:", decoded.type)
} catch {
print(error)
}
Update
In iOS 13.3+ and macOS 15.1+ it's allowed to en-/decode fragments – single JSON values which are not wrapped in a collection type
let jsonString = "4"
let jsonData = Data(jsonString.utf8)
do {
let decoded = try JSONDecoder().decode(PostType.self, from: jsonData)
print("decoded:", decoded) // -> decoded: count
} catch {
print(error)
}
In Swift 5.5+ it's even possible to en-/decode enums with associated values without any extra code. The values are mapped to a dictionary and a parameter label must be specified for each associated value
enum Rotation: Codable {
case zAxis(angle: Double, speed: Int)
}
let jsonString = #"{"zAxis":{"angle":90,"speed":5}}"#
let jsonData = Data(jsonString.utf8)
do {
let decoded = try JSONDecoder().decode(Rotation.self, from: jsonData)
print("decoded:", decoded)
} catch {
print(error)
}
How to make enums with associated types conform to Codable
This answer is similar to #Howard Lovatt's but avoids creating a PostTypeCodableForm struct and instead uses the KeyedEncodingContainer type provided by Apple as a property on Encoder and Decoder, which reduces boilerplate.
enum PostType: Codable {
case count(number: Int)
case title(String)
}
extension PostType {
private enum CodingKeys: String, CodingKey {
case count
case title
}
enum PostTypeCodingError: Error {
case decoding(String)
}
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
if let value = try? values.decode(Int.self, forKey: .count) {
self = .count(number: value)
return
}
if let value = try? values.decode(String.self, forKey: .title) {
self = .title(value)
return
}
throw PostTypeCodingError.decoding("Whoops! \(dump(values))")
}
func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: CodingKeys.self)
switch self {
case .count(let number):
try container.encode(number, forKey: .count)
case .title(let value):
try container.encode(value, forKey: .title)
}
}
}
This code works for me on Xcode 9b3.
import Foundation // Needed for JSONEncoder/JSONDecoder
let encoder = JSONEncoder()
encoder.outputFormatting = .prettyPrinted
let decoder = JSONDecoder()
let count = PostType.count(number: 42)
let countData = try encoder.encode(count)
let countJSON = String.init(data: countData, encoding: .utf8)!
print(countJSON)
// {
// "count" : 42
// }
let decodedCount = try decoder.decode(PostType.self, from: countData)
let title = PostType.title("Hello, World!")
let titleData = try encoder.encode(title)
let titleJSON = String.init(data: titleData, encoding: .utf8)!
print(titleJSON)
// {
// "title": "Hello, World!"
// }
let decodedTitle = try decoder.decode(PostType.self, from: titleData)
Swift would throw a .dataCorrupted error if it encounters unknown enum value. If your data is coming from a server, it can send you an unknown enum value at any time (bug server side, new type added in an API version and you want the previous versions of your app to handle the case gracefully, etc), you'd better be prepared, and code "defensive style" to safely decode your enums.
Here is an example on how to do it, with or without associated value
enum MediaType: Decodable {
case audio
case multipleChoice
case other
// case other(String) -> we could also parametrise the enum like that
init(from decoder: Decoder) throws {
let label = try decoder.singleValueContainer().decode(String.self)
switch label {
case "AUDIO": self = .audio
case "MULTIPLE_CHOICES": self = .multipleChoice
default: self = .other
// default: self = .other(label)
}
}
}
And how to use it in a enclosing struct:
struct Question {
[...]
let type: MediaType
enum CodingKeys: String, CodingKey {
[...]
case type = "type"
}
extension Question: Decodable {
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
[...]
type = try container.decode(MediaType.self, forKey: .type)
}
}
To extend on #Toka's answer, you may too add a raw representable value to the enum, and use the default optional constructor to build the enum without a switch:
enum MediaType: String, Decodable {
case audio = "AUDIO"
case multipleChoice = "MULTIPLE_CHOICES"
case other
init(from decoder: Decoder) throws {
let label = try decoder.singleValueContainer().decode(String.self)
self = MediaType(rawValue: label) ?? .other
}
}
It may be extended using a custom protocol that allows to refactor the constructor:
protocol EnumDecodable: RawRepresentable, Decodable {
static var defaultDecoderValue: Self { get }
}
extension EnumDecodable where RawValue: Decodable {
init(from decoder: Decoder) throws {
let value = try decoder.singleValueContainer().decode(RawValue.self)
self = Self(rawValue: value) ?? Self.defaultDecoderValue
}
}
enum MediaType: String, EnumDecodable {
static let defaultDecoderValue: MediaType = .other
case audio = "AUDIO"
case multipleChoices = "MULTIPLE_CHOICES"
case other
}
It can also be easily extended for throwing an error if an invalid enum value was specified, rather than defaulting on a value. Gist with this change is available here: https://gist.github.com/stephanecopin/4283175fabf6f0cdaf87fef2a00c8128.
The code was compiled and tested using Swift 4.1/Xcode 9.3.
A variant of #proxpero's response that is terser would be to formulate the decoder as:
public init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
guard let key = values.allKeys.first else { throw err("No valid keys in: \(values)") }
func dec<T: Decodable>() throws -> T { return try values.decode(T.self, forKey: key) }
switch key {
case .count: self = try .count(dec())
case .title: self = try .title(dec())
}
}
func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: CodingKeys.self)
switch self {
case .count(let x): try container.encode(x, forKey: .count)
case .title(let x): try container.encode(x, forKey: .title)
}
}
This permits the compiler to exhaustively verify the cases, and also doesn't suppress the error message for the case where the encoded value doesn't match the key's expected value.
Actually the answers above are really great, but they are missing some details for what many people need in a continuously developed client/server project. We develop an app while our backend continually evolves over time, which means some enum cases will change that evolution. So we need an enum decoding strategy that is able to decode arrays of enums that contain unknown cases. Otherwise decoding the object that contains the array simply fails.
What I did is quite simple:
enum Direction: String, Decodable {
case north, south, east, west
}
struct DirectionList {
let directions: [Direction]
}
extension DirectionList: Decodable {
public init(from decoder: Decoder) throws {
var container = try decoder.unkeyedContainer()
var directions: [Direction] = []
while !container.isAtEnd {
// Here we just decode the string from the JSON which always works as long as the array element is a string
let rawValue = try container.decode(String.self)
guard let direction = Direction(rawValue: rawValue) else {
// Unknown enum value found - ignore, print error to console or log error to analytics service so you'll always know that there are apps out which cannot decode enum cases!
continue
}
// Add all known enum cases to the list of directions
directions.append(direction)
}
self.directions = directions
}
}
Bonus: Hide implementation > Make it a Collection
To hide implementation detail is always a good idea. For this you'll need just a little bit more code. The trick is to conform DirectionsList to Collection and make your internal list array private:
struct DirectionList {
typealias ArrayType = [Direction]
private let directions: ArrayType
}
extension DirectionList: Collection {
typealias Index = ArrayType.Index
typealias Element = ArrayType.Element
// The upper and lower bounds of the collection, used in iterations
var startIndex: Index { return directions.startIndex }
var endIndex: Index { return directions.endIndex }
// Required subscript, based on a dictionary index
subscript(index: Index) -> Element {
get { return directions[index] }
}
// Method that returns the next index when iterating
func index(after i: Index) -> Index {
return directions.index(after: i)
}
}
You can read more about conforming to custom collections in this blog post by John Sundell: https://medium.com/#johnsundell/creating-custom-collections-in-swift-a344e25d0bb0
You can do what you want, but it is a bit involved :(
import Foundation
enum PostType: Codable {
case count(number: Int)
case comment(text: String)
init(from decoder: Decoder) throws {
self = try PostTypeCodableForm(from: decoder).enumForm()
}
func encode(to encoder: Encoder) throws {
try PostTypeCodableForm(self).encode(to: encoder)
}
}
struct PostTypeCodableForm: Codable {
// All fields must be optional!
var countNumber: Int?
var commentText: String?
init(_ enumForm: PostType) {
switch enumForm {
case .count(let number):
countNumber = number
case .comment(let text):
commentText = text
}
}
func enumForm() throws -> PostType {
if let number = countNumber {
guard commentText == nil else {
throw DecodeError.moreThanOneEnumCase
}
return .count(number: number)
}
if let text = commentText {
guard countNumber == nil else {
throw DecodeError.moreThanOneEnumCase
}
return .comment(text: text)
}
throw DecodeError.noRecognizedContent
}
enum DecodeError: Error {
case noRecognizedContent
case moreThanOneEnumCase
}
}
let test = PostType.count(number: 3)
let data = try JSONEncoder().encode(test)
let string = String(data: data, encoding: .utf8)!
print(string) // {"countNumber":3}
let result = try JSONDecoder().decode(PostType.self, from: data)
print(result) // count(3)
Features
Simple use. One line in Decodable instance: line eg let enum: DecodableEnum<AnyEnum>
Is decoded with standard mapping mechanism: JSONDecoder().decode(Model.self, from: data)
covered case of receiving unknown data (for example, mapping a Decodable object will not fail if you receive unexpected data)
handle/deliver mapping or decoding errors
Details
Xcode 12.0.1 (12A7300)
Swift 5.3
Solution
import Foundation
enum DecodableEnum<Enum: RawRepresentable> where Enum.RawValue == String {
case value(Enum)
case error(DecodingError)
var value: Enum? {
switch self {
case .value(let value): return value
case .error: return nil
}
}
var error: DecodingError? {
switch self {
case .value: return nil
case .error(let error): return error
}
}
enum DecodingError: Error {
case notDefined(rawValue: String)
case decoding(error: Error)
}
}
extension DecodableEnum: Decodable {
init(from decoder: Decoder) throws {
do {
let rawValue = try decoder.singleValueContainer().decode(String.self)
guard let layout = Enum(rawValue: rawValue) else {
self = .error(.notDefined(rawValue: rawValue))
return
}
self = .value(layout)
} catch let err {
self = .error(.decoding(error: err))
}
}
}
Usage sample
enum SimpleEnum: String, Codable {
case a, b, c, d
}
struct Model: Decodable {
let num: Int
let str: String
let enum1: DecodableEnum<SimpleEnum>
let enum2: DecodableEnum<SimpleEnum>
let enum3: DecodableEnum<SimpleEnum>
let enum4: DecodableEnum<SimpleEnum>?
}
let dictionary: [String : Any] = ["num": 1, "str": "blablabla", "enum1": "b", "enum2": "_", "enum3": 1]
let data = try! JSONSerialization.data(withJSONObject: dictionary)
let object = try JSONDecoder().decode(Model.self, from: data)
print("1. \(object.enum1.value)")
print("2. \(object.enum2.error)")
print("3. \(object.enum3.error)")
print("4. \(object.enum4)")
A lot of good approaches here, but I have not seen one discussing enums with more than one value, although it can be deduced from examples - maybe someone can find a use for this one:
import Foundation
enum Tup {
case frist(String, next: Int)
case second(Int, former: String)
enum TupType: String, Codable {
case first
case second
}
enum CodingKeys: String, CodingKey {
case type
case first
case firstNext
case second
case secondFormer
}
}
extension Tup: Codable {
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
let type = try values.decode(TupType.self, forKey: .type)
switch type {
case .first:
let str = try values.decode(String.self, forKey: .first)
let next = try values.decode(Int.self, forKey: .firstNext)
self = .frist(str, next: next)
case .second:
let int = try values.decode(Int.self, forKey: .second)
let former = try values.decode(String.self, forKey: .secondFormer)
self = .second(int, former: former)
}
}
func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: CodingKeys.self)
switch self {
case .frist(let str, next: let next):
try container.encode(TupType.first, forKey: .type)
try container.encode(str, forKey: .first)
try container.encode(next, forKey: .firstNext)
case .second(let int, former: let former):
try container.encode(TupType.second, forKey: .type)
try container.encode(int, forKey: .second)
try container.encode(former, forKey: .secondFormer)
}
}
}
let example1 = Tup.frist("123", next: 90)
do {
let encoded = try JSONEncoder().encode(example1)
print(encoded)
let decoded = try JSONDecoder().decode(Tup.self, from: encoded)
print("decoded 1 = \(decoded)")
}
catch {
print("errpr = \(error.localizedDescription)")
}
let example2 = Tup.second(10, former: "dantheman")
do {
let encoded = try JSONEncoder().encode(example2)
print(encoded)
let decoded = try JSONDecoder().decode(Tup.self, from: encoded)
print("decoded 2 = \(decoded)")
}
catch {
print("errpr = \(error.localizedDescription)")
}
Here is a simple example of how to make an enum decodable in Swift.
Sample JSON:
[
{
"title": "1904",
"artist": "The Tallest Man on Earth",
"year": "2012",
"type": "hindi"
},
{
"title": "#40",
"artist": "Dave Matthews",
"year": "1999",
"type": "english"
},
{
"title": "40oz to Freedom",
"artist": "Sublime",
"year": "1996",
"type": "english"
},
{
"title": "#41",
"artist": "Dave Matthews",
"year": "1996",
"type": "punjabi"
}
]
Model struct:
struct Song: Codable {
public enum SongType: String, Codable {
case hindi = "hindi"
case english = "english"
case punjabi = "punjabi"
case tamil = "tamil"
case none = "none"
}
let title: String
let artist: String
let year: String
let type: SongType?
}
Now, you can parse the JSON file and parse the data into an array of songs like below:
func decodeJSON() {
do {
// creating path from main bundle and get data object from the path
if let bundlePath = Bundle.main.path(forResource: "sample", ofType: "json"),
let jsonData = try String(contentsOfFile: bundlePath).data(using: .utf8) {
// decoding an array of songs
let songs = try JSONDecoder().decode([Song].self, from: jsonData)
// printing the type of song
songs.forEach { song in
print("Song type: \(song.type?.rawValue ?? "")")
}
}
} catch {
print(error)
}
}
Comment below in case of any queries.
I have the following code to extract a JSON contained within a coding key:
let value = try! decoder.decode([String:Applmusic].self, from: $0["applmusic"])
This successfully handles the following JSONs:
{
"applmusic":{
"code":"AAPL",
"quality":"good",
"line":"She told me don't worry",
}
However, fails to extract a JSON with the coding key of applmusic from the following one:
{
"applmusic":{
"code":"AAPL",
"quality":"good",
"line":"She told me don't worry",
},
"spotify":{
"differentcode":"SPOT",
"music_quality":"good",
"spotify_specific_code":"absent in apple"
},
"amazon":{
"amzncode":"SPOT",
"music_quality":"good",
"stanley":"absent in apple"
}
}
The data models for applmusic,spotify and amazon are different. However, I need only to extract applmusic and omit other coding keys.
My Swift data model is the following:
public struct Applmusic: Codable {
public let code: String
public let quality: String
public let line: String
}
The API responds with the full JSON and I cannot ask it to give me only the needed fields.
How to decode only the specific part of the json? It seems, that Decodable requires me to deserialize the whole json first, so I have to know the full data model for it.
Obviously, one of the solutions would be to create a separate Response model just to contain the applmusicparameter, but it looks like a hack:
public struct Response: Codable {
public struct Applmusic: Codable {
public let code: String
public let quality: String
public let line: String
}
// The only parameter is `applmusic`, ignoring the other parts - works fine
public let applmusic: Applmusic
}
Could you propose a better way to deal with such JSON structures?
A little bit more insight
I use it the following technique in the generic extension that automatically decodes the API responses for me. Therefore, I'd prefer to generalize a way for handling such cases, without the need to create a Root structure. What if the key I need is 3 layers deep in the JSON structure?
Here is the extension that does the decoding for me:
extension Endpoint where Response: Swift.Decodable {
convenience init(method: Method = .get,
path: Path,
codingKey: String? = nil,
parameters: Parameters? = nil) {
self.init(method: method, path: path, parameters: parameters, codingKey: codingKey) {
if let key = codingKey {
guard let value = try decoder.decode([String:Response].self, from: $0)[key] else {
throw RestClientError.valueNotFound(codingKey: key)
}
return value
}
return try decoder.decode(Response.self, from: $0)
}
}
}
The API is defined like this:
extension API {
static func getMusic() -> Endpoint<[Applmusic]> {
return Endpoint(method: .get,
path: "/api/music",
codingKey: "applmusic")
}
}
Updated: I made an extension of JSONDecoder out of this answer, you can check it here: https://github.com/aunnnn/NestedDecodable, it allows you to decode a nested model of any depth with a key path.
You can use it like this:
let post = try decoder.decode(Post.self, from: data, keyPath: "nested.post")
You can make a Decodable wrapper (e.g., ModelResponse here), and put all the logic to extract nested model with a key inside that:
struct DecodingHelper {
/// Dynamic key
private struct Key: CodingKey {
let stringValue: String
init?(stringValue: String) {
self.stringValue = stringValue
self.intValue = nil
}
let intValue: Int?
init?(intValue: Int) {
return nil
}
}
/// Dummy model that handles model extracting logic from a key
private struct ModelResponse<NestedModel: Decodable>: Decodable {
let nested: NestedModel
public init(from decoder: Decoder) throws {
let key = Key(stringValue: decoder.userInfo[CodingUserInfoKey(rawValue: "my_model_key")!]! as! String)!
let values = try decoder.container(keyedBy: Key.self)
nested = try values.decode(NestedModel.self, forKey: key)
}
}
static func decode<T: Decodable>(modelType: T.Type, fromKey key: String) throws -> T {
// mock data, replace with network response
let path = Bundle.main.path(forResource: "test", ofType: "json")!
let data = try Data(contentsOf: URL(fileURLWithPath: path), options: .mappedIfSafe)
let decoder = JSONDecoder()
// ***Pass in our key through `userInfo`
decoder.userInfo[CodingUserInfoKey(rawValue: "my_model_key")!] = key
let model = try decoder.decode(ModelResponse<T>.self, from: data).nested
return model
}
}
You can pass your desired key through userInfo of JSONDecoder ("my_model_key"). It is then converted to our dynamic Key inside ModelResponse to actually extract the model.
Then you can use it like this:
let appl = try DecodingHelper.decode(modelType: Applmusic.self, fromKey: "applmusic")
let amazon = try DecodingHelper.decode(modelType: Amazon.self, fromKey: "amazon")
let spotify = try DecodingHelper.decode(modelType: Spotify.self, fromKey: "spotify")
print(appl, amazon, spotify)
Full code:
https://gist.github.com/aunnnn/2d6bb20b9dfab41189a2411247d04904
Bonus: Deeply nested key
After playing around more, I found you can easily decode a key of arbitrary depth with this modified ModelResponse:
private struct ModelResponse<NestedModel: Decodable>: Decodable {
let nested: NestedModel
public init(from decoder: Decoder) throws {
// Split nested paths with '.'
var keyPaths = (decoder.userInfo[CodingUserInfoKey(rawValue: "my_model_key")!]! as! String).split(separator: ".")
// Get last key to extract in the end
let lastKey = String(keyPaths.popLast()!)
// Loop getting container until reach final one
var targetContainer = try decoder.container(keyedBy: Key.self)
for k in keyPaths {
let key = Key(stringValue: String(k))!
targetContainer = try targetContainer.nestedContainer(keyedBy: Key.self, forKey: key)
}
nested = try targetContainer.decode(NestedModel.self, forKey: Key(stringValue: lastKey)!)
}
Then you can use it like this:
let deeplyNestedModel = try DecodingHelper.decode(modelType: Amazon.self, fromKey: "nest1.nest2.nest3")
From this json:
{
"apple": { ... },
"amazon": {
"amzncode": "SPOT",
"music_quality": "good",
"stanley": "absent in apple"
},
"nest1": {
"nest2": {
"amzncode": "Nest works",
"music_quality": "Great",
"stanley": "Oh yes",
"nest3": {
"amzncode": "Nest works, again!!!",
"music_quality": "Great",
"stanley": "Oh yes"
}
}
}
}
Full code: https://gist.github.com/aunnnn/9a6b4608ae49fe1594dbcabd9e607834
You don't really need the nested struct Applmusic inside Response. This will do the job:
import Foundation
let json = """
{
"applmusic":{
"code":"AAPL",
"quality":"good",
"line":"She told me don't worry"
},
"I don't want this":"potatoe",
}
"""
public struct Applmusic: Codable {
public let code: String
public let quality: String
public let line: String
}
public struct Response: Codable {
public let applmusic: Applmusic
}
if let data = json.data(using: .utf8) {
let value = try! JSONDecoder().decode(Response.self, from: data).applmusic
print(value) // Applmusic(code: "AAPL", quality: "good", line: "She told me don\'t worry")
}
Edit: Addressing your latest comment
If the JSON response would change in a way that the applmusic tag is nested, you would only need to properly change your Response type. Example:
New JSON (note that applmusic is now nested in a new responseData tag):
{
"responseData":{
"applmusic":{
"code":"AAPL",
"quality":"good",
"line":"She told me don't worry"
},
"I don't want this":"potatoe",
}
}
The only change needed would be in Response:
public struct Response: Decodable {
public let applmusic: Applmusic
enum CodingKeys: String, CodingKey {
case responseData
}
enum ApplmusicKey: String, CodingKey {
case applmusic
}
public init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
let applmusicKey = try values.nestedContainer(keyedBy: ApplmusicKey.self, forKey: .responseData)
applmusic = try applmusicKey.decode(Applmusic.self, forKey: .applmusic)
}
}
The previous changes wouldn't break up any existing code, we are only fine-tuning the private implementation of how the Response parses the JSON data to correctly fetch an Applmusic object. All calls such as JSONDecoder().decode(Response.self, from: data).applmusic would remain the same.
Tip
Finally, if you want to hide the Response wrapper logic altogether, you may have one public/exposed method which will do all the work; such as:
// (fine-tune this method to your needs)
func decodeAppleMusic(data: Data) throws -> Applmusic {
return try JSONDecoder().decode(Response.self, from: data).applmusic
}
Hiding the fact that Response even exists (make it private/inaccessible), will allow you to have all the code through your app only have to call decodeAppleMusic(data:). For example:
if let data = json.data(using: .utf8) {
let value = try! decodeAppleMusic(data: data)
print(value) // Applmusic(code: "AAPL", quality: "good", line: "She told me don\'t worry")
}
Recommended read:
Encoding and Decoding Custom Types
https://developer.apple.com/documentation/foundation/archives_and_serialization/encoding_and_decoding_custom_types
Interesting question. I know that it was 2 weeks ago but I was wondering
how it can be solved using library KeyedCodable I created. Here is my proposition with generic:
struct Response<Type>: Codable, Keyedable where Type: Codable {
var responseObject: Type!
mutating func map(map: KeyMap) throws {
try responseObject <-> map[map.userInfo.keyPath]
}
init(from decoder: Decoder) throws {
try KeyedDecoder(with: decoder).decode(to: &self)
}
}
helper extension:
private let infoKey = CodingUserInfoKey(rawValue: "keyPath")!
extension Dictionary where Key == CodingUserInfoKey, Value == Any {
var keyPath: String {
set { self[infoKey] = newValue }
get {
guard let key = self[infoKey] as? String else { return "" }
return key
}
}
use:
let decoder = JSONDecoder()
decoder.userInfo.keyPath = "applmusic"
let response = try? decoder.decode(Response<Applmusic>.self, from: jsonData)
Please notice that keyPath may be nested more deeply I mean it may be eg. "responseData.services.applemusic".
In addition Response is a Codable so you can encode it without any additional work.