Related
I have this JSON format:
{
"version":"7.0.19",
"fields": ["ID","pm","age","pm_0","pm_1","pm_2","pm_3","pm_4","pm_5","pm_6","conf","pm1","pm_10","p1","p2","p3","p4","p5","p6","Humidity","Temperature","Pressure","Elevation","Type","Label","Lat","Lon","Icon","isOwner","Flags","Voc","Ozone1","Adc","CH"],
"data":[[20,0.0,1,0.0,0.0,0.0,0.0,0.0,0.0,0.0,97,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,null,null,null,1413,0,"Oakdale",40.603077,-111.83612,0,0,0,null,null,0.01,1]],
"count":11880
}
but I cannot work out how to use a Codable protocol to parse the json response.
this would be my desired model.
struct Point: Codable {
let pm2: String?
let latitude, longitude: Double?
let temp: String?
let iD: String?
enum CodingKeys: String, CodingKey {
case pm2 = "pm", temp = "Temperature", iD = "ID", latitude = "Lat", longitude = "Lon"
}
}
Here is a URL to the json
https://webbfoot.com/dataa.json
You can use Codable to parse this:
struct Response: Decodable {
let version: String
let fields: [String]
let data: [[QuantumValue?]]
let count: Int
}
enter code here
enum QuantumValue: Decodable {
case float(Float), string(String)
init(from decoder: Decoder) throws {
if let int = try? decoder.singleValueContainer().decode(Float.self) {
self = .float(float)
return
}
if let string = try? decoder.singleValueContainer().decode(String.self) {
self = .string(string)
return
}
throw QuantumError.missingValue
}
enum QuantumError:Error {
case missingValue
}
}
QuantumValue will handle both Float and String and ? will handle the null part.
This one is tricky and requires manual decoding. The principle would be to define a mapping between the fields you expect to decode and the properties of your object, then depending on the type of the property (String, Double, etc...), attempt to decode the data.
Second, since you have an array of points, you need some kind of container object to hold the array, for example:
struct Points {
var data: [Point] = []
}
First, some of your model properties don't match the type in the data, e.g. iD is a String, but the data has an Int. For simplicity, I'll redefine your model to match the data
struct Point {
var pm2: Int? = nil
var latitude: Double? = nil
var longitude: Double? = nil
var temp: Int? = nil
var iD: Int? = nil
}
Now, write the manual decoder for the parent container Points:
extension Points: Decodable {
static let mapping: [String: PartialKeyPath<Point>] = [
"pm": \Point.pm2,
"Lat": \Point.latitude,
"Lon": \Point.longitude,
"Temperature": \Point.temp,
"ID": \Point.iD
]
enum CodingKeys: CodingKey { case fields, data }
private struct Dummy: Decodable {} // see below why
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
let fields = try container.decode([String].self, forKey: .fields)
var data = try container.nestedUnkeyedContainer(forKey: .data)
while !data.isAtEnd {
var row = try data.nestedUnkeyedContainer()
var point = Point()
for field in fields {
let keyPath = Points.mapping[field]
switch keyPath {
case let kp as WritableKeyPath<Point, String?>:
point[keyPath: kp] = try row.decodeIfPresent(String.self)
case let kp as WritableKeyPath<Point, Int?>:
point[keyPath: kp] = try row.decodeIfPresent(Int.self)
case let kp as WritableKeyPath<Point, Double?>:
point[keyPath: kp] = try row.decodeIfPresent(Double.self)
default:
// this is a hack to skip this value
let _ = try? row.decode(Dummy.self)
}
}
self.data.append(point)
}
}
}
Once you have that, you can decode the JSON like so:
let points = try JSONDecoder().decode(Points.self, from: jsonData)
let firstPoint = points.data[0]
I'm fairly new to the swift programming language and have been trying to get this to work for the last week or so. I'm working with an existing API that returns JSON data whose structure changes a little depending on how many venues get returned.
The real structure is somewhat more complicated, but this example illustrates the problem. In one flavor of result, I get a single venue returned like:
{
"totalItems": 21,
"pageSize": 2,
"venues": {
"venue":
{
"name": "Venue Name 1"
"location": "Location A",
"showCount": "4"
}
}
}
In another flavor of result, I get an array of venues returned:
{
"totalItems": 21,
"pageSize": 2,
"venues": {
"venue":
[{
"name": "Venue Name 1"
"location": "Location A",
"showCount": "4"
},
{
"name": "Venue Name 2"
"location": "Location B",
"showCount": "2"
}]
}
}
Yes - the owner of this API should have returned an array regardless, but they didn't and it cannot be changed.
I was able to get this to decode properly for an array of venues (or even if no venues were passed), but it aborts when a single venue is passed (due to the structure variation of course). My code also worked when I changed it to accommodate a single venue, but then returns of multiple venues aborted.
What I'd like to do is decode either variation into an internal structure containing an array regardless of which variation I receive, thus making things far simpler for me to deal with programmatically afterward. Something like this:
struct Response: Decodable {
let totalItems: Int
let pageSize: Int
let venues: VenueWrapper
struct VenueWrapper: Decodable {
let venue: [Venue] // This might contain 0, 1, or more than one venues
}
struct Venue: Decodable {
let name: String
let location: String
let showCount: Int
}
}
Note: In the actual JSON response, there are actually several substructures like this in the response (e.g., a single structure vs an array of structures) which is why I felt simply creating an alternate structure was not a good solution.
I'm hoping someone has come across this before. Thanks in advance!
You can create your own decoder,
struct Response: Decodable {
let totalItems: Int
let pageSize: Int
let venues: VenueWrapper
struct VenueWrapper: Decodable {
var venue: [Venue]
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
venue = []
if let singleVenue = try? values.decode(Venue.self, forKey: CodingKeys.venue) {
//if a single venue decoded append it to array
venue.append(singleVenue)
} else if let multiVenue = try? values.decode([Venue].self, forKey: CodingKeys.venue) {
//if a multi venue decoded, set it as venue
venue = multiVenue
}
enum CodingKeys: String, CodingKey { case venue }
}
}
struct Venue: Decodable {
let name: String
let location: String
let showCount: String
}
}
There's no need for VenueWrapper. 🙅🎁
struct Response {
let totalItems: Int
let pageSize: Int
let venues: [Venue]
struct Venue {
let name: String
let location: String
let showCount: Int
}
}
You'll need to write your own initializer. Unfortunately, I don't think there's a way to eliminate the boilerplate for the not-goofily-encoded properties.
Even if you never need to encode it, making Response Codable, not just Decodable, will give you access to an auto-generated CodingKeys.
extension Response: Codable {
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
totalItems = try container.decode(Int.self, forKey: .totalItems)
pageSize = try container.decode(Int.self, forKey: .pageSize)
venues = try container.decode(key: .venues)
}
}
That last line relies on a protocol and extension which you can use for any other types that are similarly "encoded". 🙃
protocol GoofilyEncoded: Codable {
/// Must have exactly one case.
associatedtype GoofyCodingKey: CodingKey
}
extension KeyedDecodingContainer {
func decode<Decodable: GoofilyEncoded>(key: Key) throws -> [Decodable] {
let nestedContainer = try self.nestedContainer(
keyedBy: Decodable.GoofyCodingKey.self,
forKey: key
)
let key = nestedContainer.allKeys.first!
do {
return try nestedContainer.decode([Decodable].self, forKey: key)
}
catch {
return try [nestedContainer.decode(Decodable.self, forKey: key)]
}
}
}
All your types that might be encoded in arrays, or not 🤦♂️, will need a one-case enum, like so:
extension Response.Venue: GoofilyEncoded {
enum GoofyCodingKey: CodingKey {
case venue
}
}
I am trying to convert JSON data into an array but I do not really have any idea how to do it.
I get the data and save it in strings and I can also show it on display.
struct User_Hosting: Codable {
let company_name: String
let website: String
let street: String
let housenumber: String
let zip: String
let city: String
enum CodingKeys: String, CodingKey {
case company_name = "company_name"
case website = "website"
case street = "street"
case housenumber = "housenumber"
case zip = "zip"
case city = "city"
}
}
And here some other codes:
let url = URL(string: "myURL.com")
URLSession.shared.dataTask(with: url!, completionHandler: { [weak self] (data, response, error) in
guard let data = data, error == nil else {
print(error?.localizedDescription ?? "An error occurred")
return
}
DispatchQueue.main.async {
self?.dataSource = try! JSONDecoder().decode([User_Hosting].self, from: data)
}
}).resume()
}
Your CodingKeys match the property names, so you can get rid of the enum at all
struct UserHosting: Codable {
let companyName: String
let website: String
let street: String
let housenumber: String
let zip: String
let city: String
}
Since you have a some snake case keys in JSON, you can change the JSONDecoder.keyDecodingStrategy to convertFromSnakeCase, like so
let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .convertFromSnakeCase
Above decoder will treat keys such as company_name to be assigned to companyName property of your struct.
Finally you can decode your JSON in a do-catch block, so in case of an error we will have a message as to what went wrong.
do {
self.dataSource = try decoder.decode([UserHosting].self, from: data)
} catch {
print("JSON Decoding Error \(error)")
}
the data I'm getting from an API returns a single object but when there's multiple objects, it returns an array in the same key. With the current model (struct) I'm working with, the decoding fails when an array shows up.
These results are randomly ordered, meaning I can't know when I will be served an object or array.
Is there a way to create a model that takes this fact into account and can assign the correct type to cast for the value ('String' or '[String]') so that the decoding continues without problem?
This is an example of when an object is returned:
{
"firstFloor": {
"room": "Single Bed"
}
}
This is an example of when an array is returned (for the same key):
{
"firstFloor": {
"room": ["Double Bed", "Coffee Machine", "TV", "Tub"]
}
}
Example of the struct that should be able to be used as model to decode both samples above:
struct Hotel: Codable {
let firstFloor: Room
struct Room: Codable {
var room: String // the type has to change to either array '[String]' or object 'String' depending on the returned results
}
}
These results are randomly ordered, meaning I can't know when I will be served an object or array.
Here is the complete playground file:
import Foundation
// JSON with a single object
let jsonObject = """
{
"firstFloor": {
"room": "Single Bed"
}
}
""".data(using: .utf8)!
// JSON with an array instead of a single object
let jsonArray = """
{
"firstFloor": {
"room": ["Double Bed", "Coffee Machine", "TV", "Tub"]
}
}
""".data(using: .utf8)!
// Models
struct Hotel: Codable {
let firstFloor: Room
struct Room: Codable {
var room: String // the type has to change to either array '[String]' or object 'String' depending on the results of the API
}
}
// Decoding
let decoder = JSONDecoder()
let hotel = try decoder.decode(Hotel.self, from: jsonObject) //
print(hotel)
You might encapsulate the ambiguity of the result using an Enum with Associated Values (String and Array in this case), for example:
enum MetadataType: Codable {
case array([String])
case string(String)
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
do {
self = try .array(container.decode(Array.self))
} catch DecodingError.typeMismatch {
do {
self = try .string(container.decode(String.self))
} catch DecodingError.typeMismatch {
throw DecodingError.typeMismatch(MetadataType.self, DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Encoded payload not of an expected type"))
}
}
}
func encode(to encoder: Encoder) throws {
var container = encoder.singleValueContainer()
switch self {
case .array(let array):
try container.encode(array)
case .string(let string):
try container.encode(string)
}
}
}
struct Hotel: Codable {
let firstFloor: Room
struct Room: Codable {
var room: MetadataType
}
}
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")]