How can I decode partially double serialized json string using Codable protocol?
class Person : Codable {
var name : String?
var hobby : String?
}
class Family : Codable {
var person: String?
var person_: Person?
}
class PerfectFamily : Codable {
var person: Person?
}
let jsonString = "{\"person\":\"{\\\"name\\\":\\\"Mike\\\",\\\"hobby\\\":\\\"fishing\\\"}\"}"
do {
// I could do this.
let family = try JSONDecoder().decode(Family.self, from: Data(jsonString.utf8))
family.person_ = try JSONDecoder().decode(Person.self, from: Data(family.person!.utf8))
print(family)
// However I want to write more simply like this. Do you have some idea?
let perfectFamily = try JSONDecoder().decode(PerfectFamily.self, from: Data(jsonString.utf8)) // error
print(perfectFamily)
} catch {
print(error)
}
If you can't fix your double encoded json you can provide your own custom decoder method to your PerfectFamily class but I recommend using a struct:
struct Person: Codable {
let name: String
let hobby: String
}
struct PerfectFamily: Codable {
let person: Person
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
let person = try container.decode([String: String].self)["person"] ?? ""
self.person = try JSONDecoder().decode(Person.self, from: Data(person.utf8))
}
}
let json = "{\"person\":\"{\\\"name\\\":\\\"Mike\\\",\\\"hobby\\\":\\\"fishing\\\"}\"}"
do {
let person = try JSONDecoder().decode(PerfectFamily.self, from: Data(json.utf8)).person
print(person) // "Person(name: "Mike", hobby: "fishing")\n"
} catch {
print(error)
}
Related
This is a simplified model that is decoded from JSON:
struct Info: Decodable {
var text: String
var num: Int
}
struct Root: Decodable {
let info: Info
}
Sometimes I need to decode Info.text or Info.num only but sometimes both of them and to support all options I've made similar structs for decoding e.g:
// For text only
struct InfoText: Decodable {
var text: String
}
struct RootText: Decodable {
let info: InfoText
}
// For num only
struct InfoNum: Decodable {
var num: Int
}
struct RootNum: Decodable {
let info: InfoNum
}
This approach produces much cloned code and runtime checks to process the structs so is it possible to decode provided coding keys only with the single struct?
It's possible to provide any contextual information to the decoder with userInfo property and in this case we can pass an array of coding keys and use this info in the decoding process:
struct Info: Decodable {
var text: String?
var num: Int?
static var keys = CodingUserInfoKey(rawValue: "keys")!
enum CodingKeys: String, CodingKey {
case text, num
}
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
guard let keys = decoder.userInfo[Self.keys] as? [CodingKeys] else {
return
}
if keys.contains(.text) {
text = try container.decode(String.self, forKey: .text)
}
if keys.contains(.num) {
num = try container.decode(Int.self, forKey: .num)
}
}
}
struct Root: Decodable {
let info: Info
}
let json = #"{ "info" : { "text": "Hello", "num": 20 } }"#.data(using: .utf8)!
let decoder = JSONDecoder()
let keys: [Info.CodingKeys] = [.text]
decoder.userInfo[Info.keys] = keys
let root = try decoder.decode(Root.self, from: json)
print(root)
// Outputs:
Root(info: Info(text: Optional("Hello"), num: nil))
I have a JSON that has ID's in the root level:
{
"12345": {
"name": "Pim"
},
"54321": {
"name": "Dorien"
}
}
My goal is to use Codable to create an array of User objects that have both name and ID properties.
struct User: Codable {
let id: String
let name: String
}
I know how to use Codable with a single root level key and I know how to work with unknown keys. But what I'm trying to do here is a combination of both and I have no idea what to do next.
Here's what I got so far: (You can paste this in a Playground)
import UIKit
var json = """
{
"12345": {
"name": "Pim"
},
"54321": {
"name": "Dorien"
}
}
"""
let data = Data(json.utf8)
struct User: Codable {
let name: String
}
let decoder = JSONDecoder()
do {
let decoded = try decoder.decode([String: User].self, from: data)
decoded.forEach { print($0.key, $0.value) }
// 54321 User(name: "Dorien")
// 12345 User(name: "Pim")
} catch {
print("Failed to decode JSON")
}
This is what I'd like to do:
let decoder = JSONDecoder()
do {
let decoded = try decoder.decode([User].self, from: data)
decoded.forEach { print($0) }
// User(id: "54321", name: "Dorien")
// User(id: "12345", name: "Pim")
} catch {
print("Failed to decode JSON")
}
Any help is greatly appreciated.
You can use a custom coding key and setup User as below to parse unknown keys,
struct CustomCodingKey: CodingKey {
let intValue: Int?
let stringValue: String
init?(stringValue: String) {
self.intValue = Int(stringValue)
self.stringValue = stringValue
}
init?(intValue: Int) {
self.intValue = intValue
self.stringValue = "\(intValue)"
}
}
struct UserInfo: Codable {
let name: String
}
struct User: Codable {
var id: String = ""
var info: UserInfo?
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CustomCodingKey.self)
if let key = container.allKeys.first {
self.id = key.stringValue
self.info = try container.decode(UserInfo.self, forKey: key)
}
}
func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: CustomCodingKey.self)
if let key = CustomCodingKey(stringValue: self.id) {
try container.encode(self.info, forKey: key)
}
}
}
let decoder = JSONDecoder()
do {
let decoded = try decoder.decode(User.self, from: data)
print(decoded.id) // 12345
print(decoded.info!.name) // Pim
} catch {
print("Failed to decode JSON")
}
I'm attempting to parse the following json schema of array of items, itemID may not be empty. How do I make an item nil id itemID does not exist in the JSON?
[{
"itemID": "123",
"itemTitle": "Hello"
},
{},
...
]
My decodable classes are as follows:
public struct Item: : NSObject, Codable {
let itemID: String
let itemTitle: String?
}
private enum CodingKeys: String, CodingKey {
case itemID
case itemTitle
}
required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
itemID = try container.decode(String.self, forKey: .itemID)
itemTitle = try container.decodeIfPresent(String.self, forKey: .itemTitle)
super.init()
}
}
First of all, itemID is an Int and not String in your JSON response. So the struct Item looks like,
public struct Item: Codable {
let itemID: Int?
let itemTitle: String?
}
Parse the JSON like,
if let data = data {
do {
let items = try JSONDecoder().decode([Item].self, from: data).filter({$0.itemID == nil})
print(items)
} catch {
print(error)
}
}
In the above code you can simply filter out the items with itemID == nil.
How can I decode partially double serialized json string using Codable protocol?
class Person : Codable {
var name : String?
var hobby : String?
}
class Family : Codable {
var person: String?
var person_: Person?
}
class PerfectFamily : Codable {
var person: Person?
}
let jsonString = "{\"person\":\"{\\\"name\\\":\\\"Mike\\\",\\\"hobby\\\":\\\"fishing\\\"}\"}"
do {
// I could do this.
let family = try JSONDecoder().decode(Family.self, from: Data(jsonString.utf8))
family.person_ = try JSONDecoder().decode(Person.self, from: Data(family.person!.utf8))
print(family)
// However I want to write more simply like this. Do you have some idea?
let perfectFamily = try JSONDecoder().decode(PerfectFamily.self, from: Data(jsonString.utf8)) // error
print(perfectFamily)
} catch {
print(error)
}
If you can't fix your double encoded json you can provide your own custom decoder method to your PerfectFamily class but I recommend using a struct:
struct Person: Codable {
let name: String
let hobby: String
}
struct PerfectFamily: Codable {
let person: Person
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
let person = try container.decode([String: String].self)["person"] ?? ""
self.person = try JSONDecoder().decode(Person.self, from: Data(person.utf8))
}
}
let json = "{\"person\":\"{\\\"name\\\":\\\"Mike\\\",\\\"hobby\\\":\\\"fishing\\\"}\"}"
do {
let person = try JSONDecoder().decode(PerfectFamily.self, from: Data(json.utf8)).person
print(person) // "Person(name: "Mike", hobby: "fishing")\n"
} catch {
print(error)
}
How can I call didSet method using Codable protocol.
class Sample: Codable{
var text : String? {
didSet {
print("didSet") // do not call
extended_text = "***" + text! + "***"
}
}
var extended_text : String?
}
let sample_json = "{\"text\":\"sample text\"}"
let decoder = JSONDecoder()
let sample = try! decoder.decode(Sample.self, from: sample_json.data(using: .utf8)!)
print(sample.text!)
print(sample.extended_text ?? "")
Instead of using didSet you should just make extendedText a read only computed property. Note that it is Swift convention to use camelCase instead of snake_case when naming your properties:
struct Sample: Codable {
let text: String
var extendedText: String {
return "***" + text + "***"
}
}
let sampleJson = """
{"text":"sample text"}
"""
do {
let sample = try JSONDecoder().decode(Sample.self, from: Data(sampleJson.utf8))
print(sample.text) // "sample text\n"
print(sample.extendedText) // "***sample text***\n"
} catch {
print(error)
}
An alternative if your goal is to run a method when initializing your Codable struct is to write your own custom decoder:
class Sample: Codable {
let text: String
required init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
text = try container.decode(String.self)
print("did set")
}
}
let sampleJson = "{\"text\":\"sample text\"}"
let decoder = JSONDecoder()
do {
let sample = try decoder.decode([String: Sample].self, from: Data(sampleJson.utf8))
print(sample["text"]?.text ?? "")
} catch {
print(error)
}
This will print:
did set
sample text