I have a service whose response vary based on the orderNumer(input parameter which I pass to service). all most all object are same but only one object(ex meta object which is dictionary)vary based on order number. But I would like to reuse the same model class everywhere but due to different meta object can't be able to create that meta object in model class.I can achieve it by creating individual model class but not a right solution.
struct BookingInfo: Codable {
let created_time: Int
// Some other 20 key value pairs
let oms_meta: Meta /* oms_meta": {
"package": {
"description": "gzhdjjdjd"
}*/
}
// Meta for Order1
struct Meta: Codable {
let package: Description
enum CodingKeys : String, CodingKey {
case package = "package"
}
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
package = try values.decode(Description.self, forKey: .package)
}
}
// Meta for Order 2
struct Meta: Codable {
let customer_payment_details: Int
let items: Int // this can be anything dictinary or some time array of dictionary
enum CodingKeys : String, CodingKey {
case package = "customer_payment_details"
case items = "items"
}
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
customer_payment_details = try values.decode(Int.self, forKey: .package)
items = try values.decode(Int.self, forKey: .package)
}
}
Only meta parameters are varying from service to service.
Thanks in advance
If you want to only use 1 model, you should provide a variable for all the possible keys in the dictionary and set them as optional.
Let's say all orders have an orderNumber, but only some have an orderImage you could do it like this:
struct Order: Codable {
var orderNumber: Int
var orderImage: Data?
var orderName: String?
var orderDescription: String?
}
This way, the returned data only has to contain an orderNumber to be able to decode it.
Edit: You'd have to make a seperate model for each type of 'meta data' as they seem to be very different from eachother. Note that there is nothing wrong with creating a lot of model classes as long as they represent a specific data object.
[
{
"created_time": 1,
"oms_meta": {
"name": "1"
}
},
{
"created_time": 1,
"oms_meta": [
1
]
}
]
Suppose we have a response something like this, where you can have multiple oms_meta objects. So what we can do here is to specify an enum which will contain both array as well as dictionary, it doesn't matter if the service sends you array or dictionary if you need to specify other data types mentioned it in that enum. So it will be like,
struct BookingInfoElement: Codable {
let createdTime: Int?
let omsMeta: OmsMetaUnion?
enum CodingKeys: String, CodingKey {
case createdTime = "created_time"
case omsMeta = "oms_meta"
}
}
enum OmsMetaUnion: Codable {
case integerArray([Int])
case omsMetaClass(OmsMetaClass)
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
if let x = try? container.decode([Int].self) {
self = .integerArray(x)
return
}
if let x = try? container.decode(OmsMetaClass.self) {
self = .omsMetaClass(x)
return
}
throw DecodingError.typeMismatch(OmsMetaUnion.self, DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Wrong type for OmsMetaUnion"))
}
func encode(to encoder: Encoder) throws {
var container = encoder.singleValueContainer()
switch self {
case .integerArray(let x):
try container.encode(x)
case .omsMetaClass(let x):
try container.encode(x)
}
}
}
struct OmsMetaClass: Codable {
let name: String?
enum CodingKeys: String, CodingKey {
case name = "name"
}
}
typealias BookingInfo = [BookingInfoElement]
So, if you specifically want to have multiple types for a single variable you can create another enum with that multiple types and assign accordingly. You can access that variable using switch like, and check on array and dictionary types.
After doing some analyses I found the solution for my requirement. As I wanted to reuse the Model class and OMS_Meta dictionary different from product to product, I'm adding omsMeta to JSONDecoder().userInfo property
struct BookingInfo: Codable {
let created_time: Int
let oms_meta: [String: Any]
}
public static let metaUserInfo = CodingUserInfoKey(rawValue: "oms_meta")!
decoder.userInfo[BookingInfo.metaUserInfo] = jsonDecode
By doing this I can re use my model class.
It's not about decoding a property value with multiple types (int, string)..
I have an object called data it can return multiple types, What could be done at this point may look something like this :
enum MyData: Codable {
case ObjOne(groupObject)
case ObjTwo(imageObject)
init(from decoder: Decoder) throws {
let value = try decoder.singleValueContainer()
if let v = try? value.decode(groupObject.self) {
self = .ObjOne(v)
return
} else if let v = try? value.decode(imageObject.self) {
self = .ObjTwo(v)
return
}
throw Rating.ParseError.notRecognizedType(value)
}
enum ParseError: Error {
case notRecognizedType(Any)
}
}
The issue here is that i try to make MyData decode the object based on another value that was used in the previous decoding process, in short words, i want to pass a value to MyData so it can determine which to decode
I have this
enum ContentType: String, Codable {
case linear
case grid
case slider
}
And i want MyData to know about this ContentType value so MyData can determine how the flow will go,
So where did ContentType come from ? it's in the same list of properties in the previous main object, coming from something that looks like this
struct Catalog: Codable {
var dataType: ContentType?
var data: MyData?
}
What i want to achieve in more simple words ?
struct Catalog: Codable {
var dataType: ContentType?
var data: MyData<dataType>? <--// i know this is not possible,
// -- but i want MyData to know about the dataType value that will be decoded
}
--------- JSON i want to parse
[{
"data_type": "group",
"data": {
"group_id": 127 // this refers to object : groupObject
}
},
{
"data_type": "image",
"data": {
"image": "http://google.com/favicon" // this is referring : imageObject
}
}
]
You see the point above, is that "data" can return different objects, based on the value of data_type
Rather than using generics I created an empty protocol that conforms to Decodable and used that as the type for data. Then the content structs needs to conform to this protocol.
protocol MyData: Decodable {}
struct Group: MyData {
let groupId: Int
}
struct Image: MyData {
let image: String
}
struct Catalog: Decodable {
var dataType: String
var data: MyData
enum CodingKeys: String, CodingKey {
case dataType, data
}
enum ParseError: Error {
case notRecognizedType(Any)
}
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
dataType = try container.decode(String.self, forKey: .dataType)
switch dataType {
case "group":
data = try container.decode(Group.self, forKey: .data)
case "image":
data = try container.decode(Image.self, forKey: .data)
default:
throw ParseError.notRecognizedType(dataType)
}
}
}
Note that I didn't use the enum ContentType in the init because it didn't match the sample json data but that should be easily fixed.
Standard code for using this solution
do {
let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .convertFromSnakeCase
let result = try decoder.decode([Catalog].self, from: data)
print(result)
} catch {
print(error)
}
I have following general structure where data can be anyother codable object
struct GeneralResponse<T:Codable>: Codable {
let message: String
let status: Bool
let data: T?
enum CodingKeys: String, CodingKey {
case message = "Message"
case status = "Status"
case data = "Data"
}
}
I have Following Like response codable class which will be used as data in GeneralResponse
class ImgLike: Codable {
let id: Int?
let imageID, user: String?
#available(*, deprecated, message: "Do not use.")
private init() {
fatalError("Swift 4.1")
}
enum CodingKeys: String, CodingKey {
case id = "ID"
case imageID = "ImageID"
case user = "User"
}
}
Question 1 : When the token expires on API, The response data is empty {} still It show ImgLike object with all nil properties. Why it not show data to be nil ?
Then If I check object?.data == nil it is showing false !! So I need to check each property
Question 2 : In ImgLike If I am using custom encode function. GeneralResponse not parsed with ImgLike not parsed it shows error in catch statement
required init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
imageID = try values.decode(String.self, forKey: .imageID)
user = try values.decode(String.self, forKey: .user)
do {
id = Int(try values.decode(String.self, forKey: .id))
} catch {
id = try values.decode(Int.self, forKey: .id)
}
}
The equivalents of Swift-nil are JSON-null and JSON-not-set. {} is a valid dictionary in JSON and so not Swift-nil.
I guess that you mean that you get an error incase you use the custom decoder function? That‘s expected since the default decoder uses decodeIfPresent instead of decode to decode optionals since they are allowed not to be set.
And since you decode an empty dictionary {} none of the values are present/set.
Counting keys in dict to avoid decoding from JSON-{}
This CodingKey-struct accepts every key it gets.
fileprivate struct AllKeysAllowed: CodingKey {
var stringValue: String
var intValue: Int?
init?(stringValue: String) {
self.stringValue = stringValue
}
init?(intValue: Int) {
self.intValue = intValue
stringValue = "\(intValue)"
}
}
struct GeneralResponse<T:Codable>: Decodable {
let message: String
let status: Bool
let data: T?
enum CodingKeys: String, CodingKey {
case message = "Message"
case status = "Status"
case data = "Data"
}
public init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
message = try container.decode(String.self, forKey: .message)
status = try container.decode(Bool.self, forKey: .status)
Decode .data to a container which had all keys accepted.
Then the number of keys in the JSON-dictionary is readable with dataContainer.allKeys.count.
let dataContainer = try container.nestedContainer(keyedBy: AllKeysAllowed.self, forKey: .data)
if dataContainer.allKeys.count != 0 {
data = try container.decode(T.self, forKey: .data)
} else {
data = nil
}
}
}
Note that the default Codable implementation uses decodeIfPresent instead of decode. decodeIfPresent will not throw an error even if the key is not present in the JSON. It will simply return nil. So an empty JSON dictionary has no KVPs, so all the properties are set to nil.
In your custom implementation of Codable, you are using decode, which will throw an error if the key is not found.
The reason why object?.data != nil is because object?.data is a ImgLike???. You are wrapping an optional in an optional in an optional. I see that the type of object is GeneralResponse<ImgLike?>?. This will make data's type be ImgLike??. I don't think this is your intention. You probably intended to use GeneralRepsonse<ImgLike>. You might have forgotten to unwrap an optional somewhere. You also need to unwrap the outermost optional:
if let nonNilObject = object {
// nonNilObject.data is of type ImgLike?
}
As already mentioned the decoder does not treat an empty dictionary as nil.
You can add this functionality in a generic way with a tiny protocol and an extension of KeyedDecodingContainer
public protocol EmptyDictionaryRepresentable {
associatedtype CodingKeys : RawRepresentable where CodingKeys.RawValue == String
associatedtype CodingKeyType: CodingKey = Self.CodingKeys
}
extension KeyedDecodingContainer {
public func decodeIfPresent<T>(_ type: T.Type, forKey key: KeyedDecodingContainer.Key) throws -> T?
where T : Decodable & EmptyDictionaryRepresentable
{
guard contains(key) else { return nil }
let container = try nestedContainer(keyedBy: type.CodingKeyType.self, forKey: key)
return container.allKeys.isEmpty ? nil : try decode(T.self, forKey: key)
}
}
Just add EmptyDictionaryRepresentable conformance to ImgLike, the associated types are inferred.
class ImgLike: Codable, EmptyDictionaryRepresentable {
The properties in ImgLike could be even declared as non-optional
I have the following JSON code and want to parse it in Swift. I use Alamofire to get the JSON and have created a struct for the parsing:
{
"-8802586561990153106-1804221538-5":{
"zug":{
"klasse":"RB",
"nummer":"28721"
},
"ankunft":{
"zeitGeplant":"1804221603",
"zeitAktuell":"1804221603",
"routeGeplant":[
"Wiesbaden Hbf",
"Mainz Hbf"
]
},
"abfahrt":{
"zeitGeplant":"1804221604",
"zeitAktuell":"1804221604",
"routeGeplant":[
"Gro\u00df Gerau",
"Klein Gerau",
"Weiterstadt"
]
}
},
"8464567322535526441-1804221546-15":{
"zug":{
"klasse":"RB",
"nummer":"28724"
},
"ankunft":{
"zeitGeplant":"1804221657",
"zeitAktuell":"1804221708",
"routeGeplant":[
"Aschaffenburg Hbf",
"Mainaschaff"
]
},
"abfahrt":{
"zeitGeplant":"1804221658",
"zeitAktuell":"1804221709",
"routeGeplant":[
"Mainz-Bischofsheim"
]
}
}
}
I have created a struct for this that looks like this:
struct CallResponse: Codable {
struct DirectionTrain: Codable {
struct Train: Codable {
let trainClass: String
let trainNumber: String
}
struct Arrival: Codable {
let line: String
let eta: Date
let ata: Date
let platform: String
let route: [String]
}
struct Departure: Codable {
let line: String
let etd: Date
let atd: Date
let platform: String
let route: [String]
}
}
}
The rest of my code is:
Alamofire.request(url!).responseJSON { response in
switch response.result {
case .success:
let decoder = JSONDecoder()
let parsedResult = try! decoder.decode(CallResponse.self, from: response.data!)
case .failure(let error):
print(error)
}
}
When I run this code the error message is:
Thread 1: Fatal error: 'try!' expression unexpectedly raised an error: Swift.DecodingError.keyNotFound(CodingKeys(stringValue: "train", intValue: nil), Swift.DecodingError.Context(codingPath: [], debugDescription: "No value associated with key CodingKeys(stringValue: \"train\", intValue: nil) (\"train\").", underlyingError: nil))
Can anyone help me find my problem? Thank you for your answers!
The problem is merely that your structs look nothing at all like your JSON!
Your JSON is a dictionary whose keys have names like "-8802586561990153106-1804221538-5" and "8464567322535526441-1804221546-15". But I don't see you declaring any struct that deals with those keys.
Then each of those turns out to be a dictionary with keys like "zug", "ankunft", and "abfahrt". But I don't see you declaring any struct that deals with those keys either.
And then the "zug" has keys "klasse" and "nummer"; you don't have those either.
And so on.
Either your structs must look exactly like your JSON, or else you must define CodingKeys and possibly also implement init(from:) to deal with any differences between your structs and your JSON. I suspect that the keys "-8802586561990153106-1804221538-5" and "8464567322535526441-1804221546-15" are unpredictable, so you will probably have to write init(from:) in order to deal with them.
For example, I was able to decode your JSON like this (I do not really recommend using try!, but we decoded without error and it's just a test):
struct Entry : Codable {
let zug : Zug
let ankunft : AnkunftAbfahrt
let abfahrt : AnkunftAbfahrt
}
struct Zug : Codable {
let klasse : String
let nummer : String
}
struct AnkunftAbfahrt : Codable {
let zeitGeplant : String
let zeitAktuell : String
let routeGeplant : [String]
}
struct Top : Decodable {
var entries = [String:Entry]()
init(from decoder: Decoder) throws {
struct CK : CodingKey {
var stringValue: String
init?(stringValue: String) {
self.stringValue = stringValue
}
var intValue: Int?
init?(intValue: Int) {
return nil
}
}
let con = try! decoder.container(keyedBy: CK.self)
for key in con.allKeys {
self.entries[key.stringValue] =
try! con.decode(Entry.self, forKey: key)
}
}
}
// d is a Data containing your JSON
let result = try! JSONDecoder().decode(Top.self, from: d)
While using Swift4 and Codable protocols I got the following problem - it looks like there is no way to allow JSONDecoder to skip elements in an array.
For example, I have the following JSON:
[
{
"name": "Banana",
"points": 200,
"description": "A banana grown in Ecuador."
},
{
"name": "Orange"
}
]
And a Codable struct:
struct GroceryProduct: Codable {
var name: String
var points: Int
var description: String?
}
When decoding this json
let decoder = JSONDecoder()
let products = try decoder.decode([GroceryProduct].self, from: json)
Resulting products is empty. Which is to be expected, due to the fact that the second object in JSON has no "points" key, while points is not optional in GroceryProduct struct.
Question is how can I allow JSONDecoder to "skip" invalid object?
One option is to use a wrapper type that attempts to decode a given value; storing nil if unsuccessful:
struct FailableDecodable<Base : Decodable> : Decodable {
let base: Base?
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
self.base = try? container.decode(Base.self)
}
}
We can then decode an array of these, with your GroceryProduct filling in the Base placeholder:
import Foundation
let json = """
[
{
"name": "Banana",
"points": 200,
"description": "A banana grown in Ecuador."
},
{
"name": "Orange"
}
]
""".data(using: .utf8)!
struct GroceryProduct : Codable {
var name: String
var points: Int
var description: String?
}
let products = try JSONDecoder()
.decode([FailableDecodable<GroceryProduct>].self, from: json)
.compactMap { $0.base } // .flatMap in Swift 4.0
print(products)
// [
// GroceryProduct(
// name: "Banana", points: 200,
// description: Optional("A banana grown in Ecuador.")
// )
// ]
We're then using .compactMap { $0.base } to filter out nil elements (those that threw an error on decoding).
This will create an intermediate array of [FailableDecodable<GroceryProduct>], which shouldn't be an issue; however if you wish to avoid it, you could always create another wrapper type that decodes and unwraps each element from an unkeyed container:
struct FailableCodableArray<Element : Codable> : Codable {
var elements: [Element]
init(from decoder: Decoder) throws {
var container = try decoder.unkeyedContainer()
var elements = [Element]()
if let count = container.count {
elements.reserveCapacity(count)
}
while !container.isAtEnd {
if let element = try container
.decode(FailableDecodable<Element>.self).base {
elements.append(element)
}
}
self.elements = elements
}
func encode(to encoder: Encoder) throws {
var container = encoder.singleValueContainer()
try container.encode(elements)
}
}
You would then decode as:
let products = try JSONDecoder()
.decode(FailableCodableArray<GroceryProduct>.self, from: json)
.elements
print(products)
// [
// GroceryProduct(
// name: "Banana", points: 200,
// description: Optional("A banana grown in Ecuador.")
// )
// ]
I would create a new type Throwable, which can wrap any type conforming to Decodable:
enum Throwable<T: Decodable>: Decodable {
case success(T)
case failure(Error)
init(from decoder: Decoder) throws {
do {
let decoded = try T(from: decoder)
self = .success(decoded)
} catch let error {
self = .failure(error)
}
}
}
For decoding an array of GroceryProduct (or any other Collection):
let decoder = JSONDecoder()
let throwables = try decoder.decode([Throwable<GroceryProduct>].self, from: json)
let products = throwables.compactMap { $0.value }
where value is a computed property introduced in an extension on Throwable:
extension Throwable {
var value: T? {
switch self {
case .failure(_):
return nil
case .success(let value):
return value
}
}
}
I would opt for using a enum wrapper type (over a Struct) because it may be useful to keep track of the errors that are thrown as well as their indices.
Swift 5
For Swift 5 Consider using the Result enum e.g.
struct Throwable<T: Decodable>: Decodable {
let result: Result<T, Error>
init(from decoder: Decoder) throws {
result = Result(catching: { try T(from: decoder) })
}
}
To unwrap the decoded value use the get() method on the result property:
let products = throwables.compactMap { try? $0.result.get() }
The problem is that when iterating over a container, the container.currentIndex isn’t incremented so you can try to decode again with a different type.
Because the currentIndex is read only, a solution is to increment it yourself successfully decoding a dummy. I took #Hamish solution, and wrote a wrapper with a custom init.
This problem is a current Swift bug: https://bugs.swift.org/browse/SR-5953
The solution posted here is a workaround in one of the comments.
I like this option because I’m parsing a bunch of models the same way on a network client, and I wanted the solution to be local to one of the objects. That is, I still want the others to be discarded.
I explain better in my github https://github.com/phynet/Lossy-array-decode-swift4
import Foundation
let json = """
[
{
"name": "Banana",
"points": 200,
"description": "A banana grown in Ecuador."
},
{
"name": "Orange"
}
]
""".data(using: .utf8)!
private struct DummyCodable: Codable {}
struct Groceries: Codable
{
var groceries: [GroceryProduct]
init(from decoder: Decoder) throws {
var groceries = [GroceryProduct]()
var container = try decoder.unkeyedContainer()
while !container.isAtEnd {
if let route = try? container.decode(GroceryProduct.self) {
groceries.append(route)
} else {
_ = try? container.decode(DummyCodable.self) // <-- TRICK
}
}
self.groceries = groceries
}
}
struct GroceryProduct: Codable {
var name: String
var points: Int
var description: String?
}
let products = try JSONDecoder().decode(Groceries.self, from: json)
print(products)
There are two options:
Declare all members of the struct as optional whose keys can be missing
struct GroceryProduct: Codable {
var name: String
var points : Int?
var description: String?
}
Write a custom initializer to assign default values in the nil case.
struct GroceryProduct: Codable {
var name: String
var points : Int
var description: String
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
name = try values.decode(String.self, forKey: .name)
points = try values.decodeIfPresent(Int.self, forKey: .points) ?? 0
description = try values.decodeIfPresent(String.self, forKey: .description) ?? ""
}
}
A solution made possible by Swift 5.1, using the property wrapper:
#propertyWrapper
struct IgnoreFailure<Value: Decodable>: Decodable {
var wrappedValue: [Value] = []
private struct _None: Decodable {}
init(from decoder: Decoder) throws {
var container = try decoder.unkeyedContainer()
while !container.isAtEnd {
if let decoded = try? container.decode(Value.self) {
wrappedValue.append(decoded)
}
else {
// item is silently ignored.
try? container.decode(_None.self)
}
}
}
}
And then the usage:
let json = """
{
"products": [
{
"name": "Banana",
"points": 200,
"description": "A banana grown in Ecuador."
},
{
"name": "Orange"
}
]
}
""".data(using: .utf8)!
struct GroceryProduct: Decodable {
var name: String
var points: Int
var description: String?
}
struct ProductResponse: Decodable {
#IgnoreFailure
var products: [GroceryProduct]
}
let response = try! JSONDecoder().decode(ProductResponse.self, from: json)
print(response.products) // Only contains banana.
Note: The property wrapper things will only works if the response can be wrapped in a struct (i.e: not a top level array).
In that case, you can still wrap it manually (with a typealias for better readability):
typealias ArrayIgnoringFailure<Value: Decodable> = IgnoreFailure<Value>
let response = try! JSONDecoder().decode(ArrayIgnoringFailure<GroceryProduct>.self, from: json)
print(response.wrappedValue) // Only contains banana.
Ive put #sophy-swicz solution, with some modifications, into an easy to use extension
fileprivate struct DummyCodable: Codable {}
extension UnkeyedDecodingContainer {
public mutating func decodeArray<T>(_ type: T.Type) throws -> [T] where T : Decodable {
var array = [T]()
while !self.isAtEnd {
do {
let item = try self.decode(T.self)
array.append(item)
} catch let error {
print("error: \(error)")
// hack to increment currentIndex
_ = try self.decode(DummyCodable.self)
}
}
return array
}
}
extension KeyedDecodingContainerProtocol {
public func decodeArray<T>(_ type: T.Type, forKey key: Self.Key) throws -> [T] where T : Decodable {
var unkeyedContainer = try self.nestedUnkeyedContainer(forKey: key)
return try unkeyedContainer.decodeArray(type)
}
}
Just call it like this
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
self.items = try container.decodeArray(ItemType.self, forKey: . items)
}
For the example above:
let json = """
[
{
"name": "Banana",
"points": 200,
"description": "A banana grown in Ecuador."
},
{
"name": "Orange"
}
]
""".data(using: .utf8)!
struct Groceries: Codable
{
var groceries: [GroceryProduct]
init(from decoder: Decoder) throws {
var container = try decoder.unkeyedContainer()
groceries = try container.decodeArray(GroceryProduct.self)
}
}
struct GroceryProduct: Codable {
var name: String
var points: Int
var description: String?
}
let products = try JSONDecoder().decode(Groceries.self, from: json)
print(products)
Instead, You can also do like this:
struct GroceryProduct: Decodable {
var name: String
var points: Int
var description: String?
}'
and then in while getting it:
'let groceryList = try JSONDecoder().decode(Array<GroceryProduct>.self, from: responseData)'
Unfortunately Swift 4 API doesn't have failable initializer for init(from: Decoder).
Only one solution that I see is implementing custom decoding, giving default value for optional fields and possible filter with needed data:
struct GroceryProduct: Codable {
let name: String
let points: Int?
let description: String
private enum CodingKeys: String, CodingKey {
case name, points, description
}
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
name = try container.decode(String.self, forKey: .name)
points = try? container.decode(Int.self, forKey: .points)
description = (try? container.decode(String.self, forKey: .description)) ?? "No description"
}
}
// for test
let dict = [["name": "Banana", "points": 100], ["name": "Nut", "description": "Woof"]]
if let data = try? JSONSerialization.data(withJSONObject: dict, options: []) {
let decoder = JSONDecoder()
let result = try? decoder.decode([GroceryProduct].self, from: data)
print("rawResult: \(result)")
let clearedResult = result?.filter { $0.points != nil }
print("clearedResult: \(clearedResult)")
}
I improved on #Hamish's for the case, that you want this behaviour for all arrays:
private struct OptionalContainer<Base: Codable>: Codable {
let base: Base?
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
base = try? container.decode(Base.self)
}
}
private struct OptionalArray<Base: Codable>: Codable {
let result: [Base]
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
let tmp = try container.decode([OptionalContainer<Base>].self)
result = tmp.compactMap { $0.base }
}
}
extension Array where Element: Codable {
init(from decoder: Decoder) throws {
let optionalArray = try OptionalArray<Element>(from: decoder)
self = optionalArray.result
}
}
Swift 5
Inspired with previous answers I decode inside Result enum extension.
What do you think about it?
extension Result: Decodable where Success: Decodable, Failure == DecodingError {
public init(from decoder: Decoder) throws {
let container: SingleValueDecodingContainer = try decoder.singleValueContainer()
do {
self = .success(try container.decode(Success.self))
} catch {
if let decodingError = error as? DecodingError {
self = .failure(decodingError)
} else {
self = .failure(DecodingError.dataCorrupted(.init(codingPath: [], debugDescription: error.localizedDescription)))
}
}
}
}
Usage
let listResult = try? JSONDecoder().decode([Result<SomeObject, DecodingError>].self, from: ##YOUR DATA##)
let list: [SomeObject] = listResult.compactMap {try? $0.get()}
#Hamish's answer is great. However, you can reduce FailableCodableArray to:
struct FailableCodableArray<Element : Codable> : Codable {
var elements: [Element]
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
let elements = try container.decode([FailableDecodable<Element>].self)
self.elements = elements.compactMap { $0.wrapped }
}
func encode(to encoder: Encoder) throws {
var container = encoder.singleValueContainer()
try container.encode(elements)
}
}
I had a similar issue recently, but slightly different.
struct Person: Codable {
var name: String
var age: Int
var description: String?
var friendnamesArray:[String]?
}
In this case, if one of the element in friendnamesArray is nil, the whole object is nil while decoding.
And the right way to handle this edge case is to declare the string array[String] as array of optional strings[String?] as below,
struct Person: Codable {
var name: String
var age: Int
var description: String?
var friendnamesArray:[String?]?
}
You made the description optional, you should also make the points field optional if there is a chance it could be nil, such as this:
struct GroceryProduct: Codable {
var name: String
var points: Int?
var description: String?
}
Just make sure you safe-unwrap it however you see fit for it's use. I'm guessing nil points == 0 in the actual use case so an example could be:
let products = try JSONDecoder().decode([GroceryProduct].self, from: json)
for product in products {
let name = product.name
let points = product.points ?? 0
let description = product.description ?? ""
ProductView(name, points, description)
}
or in-line:
let products = try JSONDecoder().decode([GroceryProduct].self, from: json)
for product in products {
ProductView(product.name, product.points ?? 0, product.description ?? "")
}
I come up with this KeyedDecodingContainer.safelyDecodeArray that provides a simple interface:
extension KeyedDecodingContainer {
/// The sole purpose of this `EmptyDecodable` is allowing decoder to skip an element that cannot be decoded.
private struct EmptyDecodable: Decodable {}
/// Return successfully decoded elements even if some of the element fails to decode.
func safelyDecodeArray<T: Decodable>(of type: T.Type, forKey key: KeyedDecodingContainer.Key) -> [T] {
guard var container = try? nestedUnkeyedContainer(forKey: key) else {
return []
}
var elements = [T]()
elements.reserveCapacity(container.count ?? 0)
while !container.isAtEnd {
/*
Note:
When decoding an element fails, the decoder does not move on the next element upon failure, so that we can retry the same element again
by other means. However, this behavior potentially keeps `while !container.isAtEnd` looping forever, and Apple does not offer a `.skipFailable`
decoder option yet. As a result, `catch` needs to manually skip the failed element by decoding it into an `EmptyDecodable` that always succeed.
See the Swift ticket https://bugs.swift.org/browse/SR-5953.
*/
do {
elements.append(try container.decode(T.self))
} catch {
if let decodingError = error as? DecodingError {
Logger.error("\(#function): skipping one element: \(decodingError)")
} else {
Logger.error("\(#function): skipping one element: \(error)")
}
_ = try? container.decode(EmptyDecodable.self) // skip the current element by decoding it into an empty `Decodable`
}
}
return elements
}
}
The potentially infinite loop while !container.isAtEnd is a concern, and it's addressed by using EmptyDecodable.
A much simpler attempt:
Why don't you declare points as optional or make the array contain optional elements
let products = [GroceryProduct?]
Features:
Simple use. One line in Decodable instance: let array: CompactDecodableArray<Int>
Is decoded with standard mapping mechanism: JSONDecoder().decode(Model.self, from: data)
skips incorrect elements (returns array with only successful mapped elements)
Details
Xcode 12.1 (12A7403)
Swift 5.3
Solution
class CompactDecodableArray<Element>: Decodable where Element: Decodable {
private(set) var elements = [Element]()
required init(from decoder: Decoder) throws {
guard var unkeyedContainer = try? decoder.unkeyedContainer() else { return }
while !unkeyedContainer.isAtEnd {
if let value = try? unkeyedContainer.decode(Element.self) {
elements.append(value)
} else {
unkeyedContainer.skip()
}
}
}
}
// https://forums.swift.org/t/pitch-unkeyeddecodingcontainer-movenext-to-skip-items-in-deserialization/22151/17
struct Empty: Decodable { }
extension UnkeyedDecodingContainer {
mutating func skip() { _ = try? decode(Empty.self) }
}
Usage
struct Model2: Decodable {
let num: Int
let str: String
}
struct Model: Decodable {
let num: Int
let str: String
let array1: CompactDecodableArray<Int>
let array2: CompactDecodableArray<Int>?
let array4: CompactDecodableArray<Model2>
}
let dictionary: [String : Any] = ["num": 1, "str": "blablabla",
"array1": [1,2,3],
"array3": [1,nil,3],
"array4": [["num": 1, "str": "a"], ["num": 2]]
]
let data = try! JSONSerialization.data(withJSONObject: dictionary)
let object = try JSONDecoder().decode(Model.self, from: data)
print("1. \(object.array1.elements)")
print("2. \(object.array2?.elements)")
print("3. \(object.array4.elements)")
Console
1. [1, 2, 3]
2. nil
3. [__lldb_expr_25.Model2(num: 1, str: "a")]