Use of Codable and Coding Key with JSONEncoder and JSONDecoder in Swift 4

Codable is added with Xcode 9, iOS 11 and Swift 4. Codable is used to make your data types encodable and decodable for compatibility with external representations such as JSON.
Codable use to support both encoding and decoding, declare conformance to Codable, which combines the Encodable and Decodable protocols. This process is known as making your types codable.

Let’s Take an Example with Structure of Movie, here we have defined the structure as Codable. So, We can encode and decode it easily.

struct Movie : Codable {
    enum MovieGenere: String, Codable {
        case horror, skifi, comedy, adventure, animation
    }
    var name : String
    var moviesGenere : [MovieGenere]
    var rating : Int
}

struct Movie : Codable {

enum MovieGenere: String, Codable {

case horror, skifi, comedy, adventure, animation

}

var name : String

var moviesGenere : [MovieGenere]

var rating : Int

}

We can create a object from movie like as:

let upMovie = Movie(name: "Up", moviesGenere: [.comedy , .adventure, .animation], rating : 4)

1	let upMovie = Movie(name: "Up", moviesGenere: [.comedy , .adventure, .animation], rating : 4)

The upMovie contains the name “Up” and it’s movieGenere is comedy, adventure and animation witch contains 4 rating out of 5.

Encode

JSONEncoder is an object that encodes instances of a data type as JSON objects. JSONEncoder supports the Codable object.

// Encode data
let jsonEncoder = JSONEncoder()
do {
    let jsonData = try jsonEncoder.encode(upMovie)
    let jsonString = String(data: jsonData, encoding: .utf8)
    print("JSON String : " + jsonString!)
}
catch {
}

// Encode data

let jsonEncoder = JSONEncoder()

do {

let jsonData = try jsonEncoder.encode(upMovie)

let jsonString = String(data: jsonData, encoding: .utf8)

print("JSON String : " + jsonString!)

}

catch {

}

JSONEncoder will give us the JSON data which is used to retrieve JSON string.
Output string will be like :

{
  "name": "Up",
  "moviesGenere": [
    "comedy",
    "adventure",
    "animation"
  ],
  "rating": 4
}

{

"name": "Up",

"moviesGenere": [

"comedy",

"adventure",

"animation"

"rating": 4

}

Decode

JSONDecoder is an object that decodes instances of a data type from JSON objects. We can get the object back from the JSON string.

do {
    // Decode data to object
    let jsonDecoder = JSONDecoder()
    let upMovie = try jsonDecoder.decode(Movie.self, from: jsonData)
    print("Rating : \(upMovie.name)")
    print("Rating : \(upMovie.rating)")
}
catch {
}

do {

// Decode data to object

let jsonDecoder = JSONDecoder()

let upMovie = try jsonDecoder.decode(Movie.self, from: jsonData)

print("Rating : \(upMovie.name)")

print("Rating : \(upMovie.rating)")

}

catch {

}

By decoding the JSONData we will receive the Movie object back. So we can get all the values which is saved in that object.
Output will be like:

Name : Up
Rating : 4

1 2	Name : Up Rating : 4

Coding Key

We can change the key name to create a mapping between Swift names and JSON names, use a nested enumeration named CodingKeys within the same type that adds conformance to Codable.

struct Movie : Codable {
    enum MovieGenere: String, Codable {
        case horror, skifi, comedy, adventure, animation
    }
    var name : String
    var moviesGenere : [MovieGenere]
    var rating : Int
    private enum CodingKeys: String, CodingKey {
        case name = "movie_name"
        case rating = "movie_rating"
        case moviesGenere
    }
}

struct Movie : Codable {

enum MovieGenere: String, Codable {

case horror, skifi, comedy, adventure, animation

}

var name : String

var moviesGenere : [MovieGenere]

var rating : Int

private enum CodingKeys: String, CodingKey {

case name = "movie_name"

case rating = "movie_rating"

case moviesGenere

}

Xcode Swift playground file is available at Github. Many things came with iOS 11, Xcode 9 and Swift 4.
Happy Coding 🙂

Encode

Decode

Coding Key

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