Mapping Generic API Response Using Codable or ObjectMapper

Question

I am facing a challenge regarding mapping a generic api responses against a model class using codable or object mapper. Suppose I have these api responses against different apis.

{
  "code" : 0, 
  "http_response" : 200,
  "success" : true, 
  "data" : user
}

{
  "code" : 0, 
  "http_response" : 200,
  "success" : true, 
  "data" : locations
}

{
  "code" : 0, 
  "http_response" : 200,
  "success" : true, 
  "data" : countries
}

here user, locations and countries are separate codable/mapper classes.

I will have to construct a class like this

struct APIResponse : Codable {
    let success : Bool?
    let http_response : Int?
    let code : Int?
    let data : ??
}

How I will construct my base class to handle these responses using one class or I will have construct different classes just to change "data" type according to value?

Any kind of help or suggestion will be highly appreciated.

Thanks

https://stackoverflow.com/questions/52681385/swift-codable-multiple-types — SPatel, Jan 28 '19 at 11:20

Robert Dresler · Answer 1 · 2019-01-28T08:04:16.810

Make generic constraint for you struct which says that T has to conform to Decodable and then use this type for specifing type of data

struct APIResponse<T: Decodable>: Decodable {
    var code, httpResponse: Int
    var success: Bool
    var data: T
}

struct User: Decodable {
    var name: String
}

note that I changed name of httpResponse parameter since I'm using keyDecodingStrategy which converts http_response to httpResponse

Then while decoding specify type of T

Single object

let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .convertFromSnakeCase

do {
    let responses = try decoder.decode([APIResponse<User>].self, from: data)
    let user = responses[0].data /* data of type `User` of specific response */
} catch { print(error) }

Array of objects

let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .convertFromSnakeCase

do {
    let responses = try decoder.decode([APIResponse<[User]>].self, from: data)
    let users = responses[0].data /* data of type `[User]` of specific response */
} catch { print(error) }

score 2 · Accepted Answer · answered Jan 28 '19 at 07:28

Your decoding method and APIResponse will look like this considering user, countries, locations are decodable,

struct APIResponse<T: Decodable>: Decodable {
    var data: T?
    var code: Int
    var success: Bool
    var http_response: Int
}

func decode<T: Decodable>(data: Data, ofType: T.Type) -> T? {
    do {
        let decoder = JSONDecoder()
        let res = try decoder.decode(APIResponse<T>.self, from: data)
        return res.data
    } catch let parsingError {
        print("Error", parsingError)
    }
    return nil
}

Usage

let data = Data() // From the network api 

//User
let user = decode(data, ofType: User.self)

// Countries
let countries = decode(data, ofType: [Country].self) 

// Locations
let locations = decode(data, ofType: [Location].self)

Mapping Generic API Response Using Codable or ObjectMapper

2 Answers2