How to serialize or convert Swift objects to JSON? - json

Question

This below class
class User: NSManagedObject {
#NSManaged var id: Int
#NSManaged var name: String
}
Needs to be converted to
{
"id" : 98,
"name" : "Jon Doe"
}
I tried manually passing the object to a function which sets the variables into a dictionary and returns the dictionary. But I would want a better way to accomplish this.

Answer 1

In Swift 4, you can inherit from the Codable type.
struct Dog: Codable {
var name: String
var owner: String
}
// Encode
let dog = Dog(name: "Rex", owner: "Etgar")
let jsonEncoder = JSONEncoder()
let jsonData = try jsonEncoder.encode(dog)
let json = String(data: jsonData, encoding: String.Encoding.utf8)
// Decode
let jsonDecoder = JSONDecoder()
let secondDog = try jsonDecoder.decode(Dog.self, from: jsonData)

Answer 2

Along with Swift 4 (Foundation) now it is natively supported in both ways, JSON string to an object - an object to JSON string.
Please see Apple's documentation here JSONDecoder() and here JSONEncoder()
JSON String to Object
let jsonData = jsonString.data(using: .utf8)!
let decoder = JSONDecoder()
let myStruct = try! decoder.decode(myStruct.self, from: jsonData)
Swift Object to JSONString
let encoder = JSONEncoder()
encoder.outputFormatting = .prettyPrinted
let data = try! encoder.encode(myStruct)
print(String(data: data, encoding: .utf8)!)
You can find all details and examples here Ultimate Guide to JSON Parsing With Swift 4

Answer 3

UPDATE: Codable protocol introduced in Swift 4 should be sufficient for most of the JSON parsing cases. Below answer is for people who are stuck in previous versions of Swift and for legacy reasons
EVReflection :
This works of reflection principle. This takes less code and also supports NSDictionary, NSCoding, Printable, Hashable and Equatable
Example:
class User: EVObject { # extend EVObject method for the class
var id: Int = 0
var name: String = ""
var friends: [User]? = []
}
# use like below
let json:String = "{\"id\": 24, \"name\": \"Bob Jefferson\", \"friends\": [{\"id\": 29, \"name\": \"Jen Jackson\"}]}"
let user = User(json: json)
ObjectMapper :
Another way is by using ObjectMapper. This gives more control but also takes a lot more code.
Example:
class User: Mappable { # extend Mappable method for the class
var id: Int?
var name: String?
required init?(_ map: Map) {
}
func mapping(map: Map) { # write mapping code
name <- map["name"]
id <- map["id"]
}
}
# use like below
let json:String = "{\"id\": 24, \"name\": \"Bob Jefferson\", \"friends\": [{\"id\": 29, \"name\": \"Jen Jackson\"}]}"
let user = Mapper<User>().map(json)

Answer 4

I worked a bit on a smaller solution that doesn't require inheritance. But it hasn't been tested much. It's pretty ugly atm.
https://github.com/peheje/JsonSerializerSwift
You can pass it into a playground to test it. E.g. following class structure:
//Test nonsense data
class Nutrient {
var name = "VitaminD"
var amountUg = 4.2
var intArray = [1, 5, 9]
var stringArray = ["nutrients", "are", "important"]
}
class Fruit {
var name: String = "Apple"
var color: String? = nil
var weight: Double = 2.1
var diameter: Float = 4.3
var radius: Double? = nil
var isDelicious: Bool = true
var isRound: Bool? = nil
var nullString: String? = nil
var date = NSDate()
var optionalIntArray: Array<Int?> = [1, 5, 3, 4, nil, 6]
var doubleArray: Array<Double?> = [nil, 2.2, 3.3, 4.4]
var stringArray: Array<String> = ["one", "two", "three", "four"]
var optionalArray: Array<Int> = [2, 4, 1]
var nutrient = Nutrient()
}
var fruit = Fruit()
var json = JSONSerializer.toJson(fruit)
print(json)
prints
{"name": "Apple", "color": null, "weight": 2.1, "diameter": 4.3, "radius": null, "isDelicious": true, "isRound": null, "nullString": null, "date": "2015-06-19 22:39:20 +0000", "optionalIntArray": [1, 5, 3, 4, null, 6], "doubleArray": [null, 2.2, 3.3, 4.4], "stringArray": ["one", "two", "three", "four"], "optionalArray": [2, 4, 1], "nutrient": {"name": "VitaminD", "amountUg": 4.2, "intArray": [1, 5, 9], "stringArray": ["nutrients", "are", "important"]}}

Answer 5

This is not a perfect/automatic solution but I believe this is the idiomatic and native way to do such. This way you don't need any libraries or such.
Create an protocol such as:
/// A generic protocol for creating objects which can be converted to JSON
protocol JSONSerializable {
private var dict: [String: Any] { get }
}
extension JSONSerializable {
/// Converts a JSONSerializable conforming class to a JSON object.
func json() rethrows -> Data {
try JSONSerialization.data(withJSONObject: self.dict, options: nil)
}
}
Then implement it in your class such as:
class User: JSONSerializable {
var id: Int
var name: String
var dict { return ["id": self.id, "name": self.name] }
}
Now:
let user = User(...)
let json = user.json()
Note: if you want json as a string, it is very simply to convert to a string: String(data: json, encoding .utf8)

Answer 6

Some of the above answers are completely fine, but I added an extension here, just to make it much more readable and usable.
extension Encodable {
var convertToString: String? {
let jsonEncoder = JSONEncoder()
jsonEncoder.outputFormatting = .prettyPrinted
do {
let jsonData = try jsonEncoder.encode(self)
return String(data: jsonData, encoding: .utf8)
} catch {
return nil
}
}
}
struct User: Codable {
var id: Int
var name: String
}
let user = User(id: 1, name: "name")
print(user.convertToString!)
//This will print like the following:
{
"id" : 1,
"name" : "name"
}

Answer 7

Not sure if lib/framework exists, but if you would like to do it automatically and you would like to avoid manual labour :-) stick with MirrorType ...
class U {
var id: Int
var name: String
init(id: Int, name: String) {
self.id = id
self.name = name
}
}
extension U {
func JSONDictionary() -> Dictionary<String, Any> {
var dict = Dictionary<String, Any>()
let mirror = reflect(self)
var i: Int
for i = 0 ; i < mirror.count ; i++ {
let (childName, childMirror) = mirror[i]
// Just an example how to check type
if childMirror.valueType is String.Type {
dict[childName] = childMirror.value
} else if childMirror.valueType is Int.Type {
// Convert to NSNumber for example
dict[childName] = childMirror.value
}
}
return dict
}
}
Take it as a rough example, lacks proper conversion support, lacks recursion, ... It's just MirrorType demonstration ...
P.S. Here it's done in U, but you're going to enhance NSManagedObject and then you'll be able to convert all NSManagedObject subclasses. No need to implement this in all subclasses/managed objects.

Answer 8

struct User:Codable{
var id:String?
var name:String?
init(_ id:String,_ name:String){
self.id = id
self.name = name
}
}
Now just make your object like this
let user = User("1","pawan")
do{
let userJson = try JSONEncoder().encode(parentMessage)
}catch{
fatalError("Unable To Convert in Json")
}
Then reconvert from json to Object
let jsonDecoder = JSONDecoder()
do{
let convertedUser = try jsonDecoder.decode(User.self, from: userJson.data(using: .utf8)!)
}catch{
}

Answer 9

2021 | SWIFT 5.1 | Results solution
Input data:
struct ConfigCreds: Codable {
// some params
}
usage:
// get JSON from Object
configCreds
.asJson()
.onSuccess{ varToSaveJson = $0 }
.onFailure{ _ in // any failure code }
// get object of type "ConfigCreds" from JSON
someJsonString
.decodeFromJson(type: ConfigCreds.self)
.onSuccess { configCreds = $0 }
.onFailure{ _ in // any failure code }
Back code:
#available(macOS 10.15, *)
public extension Encodable {
func asJson() -> Result<String, Error>{
JSONEncoder()
.try(self)
.flatMap{ $0.asString() }
}
}
public extension String {
func decodeFromJson<T>(type: T.Type) -> Result<T, Error> where T: Decodable {
self.asData()
.flatMap { JSONDecoder().try(type, from: $0) }
}
}
///////////////////////////////
/// HELPERS
//////////////////////////////
#available(macOS 10.15, *)
fileprivate extension JSONEncoder {
func `try`<T : Encodable>(_ value: T) -> Result<Output, Error> {
do {
return .success(try self.encode(value))
} catch {
return .failure(error)
}
}
}
fileprivate extension JSONDecoder {
func `try`<T: Decodable>(_ t: T.Type, from data: Data) -> Result<T,Error> {
do {
return .success(try self.decode(t, from: data))
} catch {
return .failure(error)
}
}
}
fileprivate extension String {
func asData() -> Result<Data, Error> {
if let data = self.data(using: .utf8) {
return .success(data)
} else {
return .failure(WTF("can't convert string to data: \(self)"))
}
}
}
fileprivate extension Data {
func asString() -> Result<String, Error> {
if let str = String(data: self, encoding: .utf8) {
return .success(str)
} else {
return .failure(WTF("can't convert Data to string"))
}
}
}
fileprivate func WTF(_ msg: String, code: Int = 0) -> Error {
NSError(code: code, message: msg)
}