How to serialize or convert Swift objects to JSON?

Question

This below class

class User: NSManagedObject {
  @NSManaged var id: Int
  @NSManaged var name: String
}

Needs to be converted to

Answer 1

2020 | SWIFT 5.1:

(also works with SWIFT 4)

---

Ready to work solution!

Usage:

var msgTemplates = [msgTemlate]()

// load from file
msgTemplates = try! Serializer.load(from: url)!

// save to file
Serializer.save(data: msgTemplates, to: url)

---

The following code resolve 3 things:

• 1 string to save file
• 1 string to load file
• ability to get/print JSON of some Codable element with element.toJsonString

    import Foundation

    public class Serializer{
        static func save<T>(data: T, to url: URL) where T : Encodable{
            guard let json = data.toJsonString else { return }

            do {
                try json.write(to: url, atomically: true, encoding: String.Encoding.utf8)
            }
            catch { /* error handling here */ }
        }

        static func load<T>(from url: URL) throws -> T? where T : Decodable {
            let decoder = JSONDecoder()
            decoder.dateDecodingStrategy = .iso8601 // for human-read date format

            guard let dataStr = try? String(contentsOf: url, encoding: String.Encoding.utf8 ),
                  let data = dataStr.data(using: String.Encoding.utf8 ),
                  let result = try? decoder.decode( T.self , from: data)
            else { return nil }

            return result
        }
    }

    extension Encodable {
        var toJsonString: String? {
            let encoder = JSONEncoder()
            encoder.outputFormatting = .prettyPrinted  // nice formatted for reading by human
            encoder.dateEncodingStrategy = .iso8601    // for human-read date format

            do {
                let jsonData = try encoder.encode(self)
                return String(data: jsonData, encoding: .utf8)
            } catch {
                return nil
            }
        }
    }

---

PS: and ofc data must be Codable:

struct msgTemlate: Codable { 
     //some params
}

---

PS2: in case of msgTemlate have enums, they are also must be Codable

Answer 2

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 3

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 4

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 5

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.utf16)

// Decode
let jsonDecoder = JSONDecoder()
let secondDog = try jsonDecoder.decode(Dog.self, from: jsonData)

Answer 6

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"]}}