I have the following json data and trying to parse it, but I get number of objects, but object itself in the array all are nil.
I do not want to decode the origin in the following json object.
By the way, the following string is first converted to data and then passed it to parse function below.
Data is follows:
[
[
{"id": "152478", "age": 20},
{"character": "king","isDead":"no", "canMove" :"yes", "origin" :"south africa"}
],
[
{"id": "887541", "age": 22},
{"character": "lion", "isDead":"no", "canMove" :"yes", "origin" :"south america"}
]
]
Models
struct A: Codable {
let id: String?
let age: Int?
enum CodingKeys: String, CodingKey {
case id
case age
}
}
struct B: Codable {
let character, isDead, canMove: String?
enum CodingKeys: String, CodingKey {
case character
case isDead
case canMove
}
}
struct AB :Codable {
let a: A
let b: B
init(from decoder: Decoder) throws {
guard var container = try? decoder.unkeyedContainer() else {
//no error here!!!
fatalError()
}
print(container)
guard let a = try? container.decode(A.self),
let b = try? container.decode(B.self)
else {
// throw since we didn't find A first, followed by B
throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: [], debugDescription: "The given data was not valid JSON.", underlyingError: nil)
)
}
self.a = a
self.b = b
}
}
ViewModel
private func parse(jsonData : Data){
do {
let decoder = JSONDecoder()
let response = try decoder.decode([AB].self, from: jsonData)
print(response)
}
catch (let error as NSError) {
print(error)
}
}
UPDATE:
By the way, the following code works. I wonder why above code does not handle?
private func parseData(jsonData : Data)
{
do {
response = try JSONSerialization.jsonObject(with: jsonData) as! [[[String: Any]]]
for i in 0..<response.count
{
for j in 0..<response[i].count
{
if j == 0
{
let jsonDat = (try? JSONSerialization.data(withJSONObject:response[i][j]))!
let b = try JSONDecoder().decode(A.self, from: jsonDat)
}
else if j == 1
{
let jsonDatt = (try? JSONSerialization.data(withJSONObject:response[i][j]))!
let a = try JSONDecoder().decode(B.self, from: jsonDatt)
}
}
}
print(response)
}
catch let error as NSError {
print(error)
}
}
UPDATE II:
If I make the following changes [AB] --> [[AB]], and then I call it as follows, it decodes data, but in the array I end up, A object has values, but B nil, or vice versa.
let response = try decoder.decode([[AB]].self, from: jsonData)
guard var container = try? decoder.singleValueContainer() else
{
fatalError()
}
I just tried this stripped-down version of your code in a playground
let json = """
[
[
{"id": "152478", "age": 20},
{"character": "king","isDead":"no", "canMove" :"yes", "origin" :"south africa"}
],
[
{"id": "887541", "age": 22},
{"character": "lion", "isDead":"no", "canMove" :"yes", "origin" :"south america"}
]
]
""".data(using: .utf8)!
struct A: Codable {
let id: String
let age: Int
}
struct B: Codable {
let character, isDead, canMove: String
}
struct AB: Codable {
let a: A
let b: B
init(from decoder: Decoder) throws {
var container = try decoder.unkeyedContainer()
self.a = try container.decode(A.self)
self.b = try container.decode(B.self)
}
}
do {
let ab = try JSONDecoder().decode([AB].self, from: json)
print(ab.count)
print(ab[0].a.id)
print(ab[0].b.character)
print(ab[1].a.id)
print(ab[1].b.character)
} catch {
print(error)
}
and it works just fine. Maybe this helps figuring out what's going on.
Here's an simplified version of the class:
class Movie: Codable {
var name: String
var genre: MovieGenre
init(name: String, genre: MovieGenre) {
self.name = name
self.genre = genre
}
}
enum MovieGenre: String, Codable {
case action
case drama
case horror
}
And the JSON:
{
"name" : "Test",
"genre" : 1
}
I know the relation between the JSON genre value and the MovieGenre enum is:
1 = action
2 = drama
3 = horror
Using JSONDecoder, how can I convert the JSON genre Int value to my enum MovieGenre?
I would like not to have to write an init from decoder, because it would be very verbose having to convert each attribute manually.
Here's an example:
let movie = Movie(name: "Test", genre: .action)
let jsonEncoder = JSONEncoder()
let jsonDecoder = JSONDecoder()
do {
// encoding
let jsonData = try jsonEncoder.encode(movie)
let jsonString = String(data: jsonData, encoding: .utf8)
print("JSON String : " + jsonString!) // prints: JSON String : {"name":"Test","genre":"action"}
// decoding
let json = "{\"name\":\"Test\",\"genre\":1}".data(using: .utf8)!
_ = try jsonDecoder.decode(Movie.self, from: json)
} catch {
print(error) // prints: typeMismatch(Swift.String, Swift.DecodingError.Context(codingPath: [CodingKeys(stringValue: "genre", intValue: nil)], debugDescription: "Expected to decode String but found a number instead.", underlyingError: nil))
}
Your type for your enum does not match with the type in the JSON.
I changed the Type for your enum to Int and set the initial value for action (as the default would be 0) and got the expected result without custom decoding.
Trying this in a playground:
import UIKit
import PlaygroundSupport
let jsonData = """
{
"name" : "Test",
"genre" : 1
}
""".data(using: .utf8)!
class Movie: Codable {
var name: String
var genre: MovieGenre
init(name: String, genre: MovieGenre) {
self.name = name
self.genre = genre
}
}
enum MovieGenre: Int, Codable {
case action = 1
case drama
case horror
}
let decoder = JSONDecoder()
let result = try? decoder.decode(Movie.self, from: jsonData)
print(result?.name)
print(result?.genre)
print(result?.genre.rawValue)
Output is:
Optional("Test")
Optional(__lldb_expr_39.MovieGenre.action)
Optional(1)
This should also encode in the same way.
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)
Unable to decode json response from server with Decodable
A help or a suggestion would be appreciated
JSON:
*
["error": <__NSArrayM 0x60400044ab60>(
)
, "data": <__NSArrayM 0x60400044fae0>(
{
id = 0;
name = all;
},
{
id = 1;
name = "MONTHLY SUPPLIES";
}
)
, "success": 1]
//Response is in Dictionary of Array
Code:
struct CategoryData: Decodable {
var categories: [Category]! // Array
//codable enum case
private enum DataKeys: String, CodingKey {
case data
}
// Manually decode values
public init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: DataKeys.self)
let data = try container.decode([[String: String]].self, forKey: .data)
print(data)
/* Category is a class here contains 2 variable name and id.*/
categories = data.map({ Category($0) })
print(categories)
}
}
Juse make your Category structure conform to Codable. You should also map categories to "data".
//: Playground - noun: a place where people can play
import Foundation
struct CategoryData: Codable {
let categories: [Category]
private enum CodingKeys: String, CodingKey {
case categories = "data"
}
}
struct Category: Codable {
let id: Int
let name: String
}
// create json mock by encoding
let category1 = Category(id: 0, name: "all")
let category2 = Category(id: 1, name: "MONTHLY SUPPLIES")
let categoryData = CategoryData(categories: [category1, category2])
let json = try! JSONEncoder().encode(categoryData)
print(String(bytes: json, encoding: String.Encoding.utf8)) // Optional("{\"data\":[{\"id\":0,\"name\":\"all\"},{\"id\":1,\"name\":\"MONTHLY SUPPLIES\"}]}")
// create category data by decoding json (your actual question)
do {
let categoryDataAgain = try JSONDecoder().decode(CategoryData.self, from: json)
for category in categoryDataAgain.categories {
print(category.id) // 0, 1
print(category.name) // "all", "MONTLY SUPPLIES"
}
} catch {
print("something went wrong")
}
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")]