class City: NSObject, NSCoding
{
    var name: String?
    var id: Int?
    
    required init?(coder aDecoder: NSCoder)
    {
        self.name = aDecoder.decodeObject(forKey: "name") as? String
        self.id = aDecoder.decodeObject(forKey: "id") as? Int
    }
    
    func encode(with aCoder: NSCoder)
    {
        aCoder.encode(self.name, forKey: "name")
        aCoder.encode(self.id, forKey: "id")
    }
}

struct Photo: Codable
{
    //String, URL, Bool and Date conform to Codable.
    var title: String
    var url: URL
    var isSample: Bool
    
    //The Dictionary is of type [String:String] and String already conforms to Codable.
    var metaData: [String:String]
    
    //PhotoType and Size are also Codable types
    var type: PhotoType
    var size: Size
}

struct Size: Codable
{
    var height: Double
    var width: Double
}

enum PhotoType: String, Codable
{
    case flower
    case animal
    case fruit
    case vegetable
}

let photoObject = Photo(title: "Hibiscus", 
url: URL(string: "https://www.flowers.com/hibiscus")!, 
isSample: false, metaData: ["color" : "red"],
 type: .flower, size: Size(width: 200, height: 200))

let encodedData = try? JSONEncoder().encode(photoObject)

let jsonString = """
{
    "type":"fruit",
    "size":{
               "width":150,
               "height":150
           },
    "title":"Apple",
    "url":"https:\\/\\/www.fruits.com\\/apple",
    "isSample":true,
    "metaData":{
                  "color":"green"
               }
}
"""
if let jsonData = jsonString.data(using: .utf8)
{
    let photoObject = try? JSONDecoder().decode(Photo.self, from: jsonData)
}

struct Photo: Codable
{
    //...Other properties (described in Code Snippet - 1)...
    
    //This property is not included in the CodingKeys enum and hence will not be encoded/decoded.
    var format: String = "png"
    
    enum CodingKeys: String, CodingKey
    {
        case title = "name"
        case url = "link"
        case isSample
        case metaData
        case type
        case size
    }
}