How to discriminate while decoding using Codable Protocol in Swift? - ios

Question

I am using Swift's Codable Protocol. I have shared the code.
I want the variable boss in the class Employee to acquire the type based on the personType String in the Person class. I want to use personType as discriminator. Response coming from the server will be different every time based on the personType value.
In Employee class, I have declared the boss variable with Person type. I want it to decode for type Employee if the personType string in the Person class is "Employee" and decode for type Boss if the personType string is "Boss". If it is null I simply want it to decode for type Person.
Any help would be really appreciated.
public class Person: Codable {
public let address: String
public let age: Int
public let name: String
public let uid: String
public let personType: String?
private enum CodingKeys: String, CodingKey {
case address
case age
case name
case uid
case personType
}
required public init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
address = try container.decode(String.self, forKey: .address)
age = try container.decode(Int.self, forKey: .age)
name = try container.decode(String.self, forKey: .name)
uid = try container.decode(String.self, forKey: .uid)
personType = try container.decodeIfPresent(String.self, forKey: .personType)
}
}
public class Employee: Person {
public let department: String
public let dependents: [Person]?
public let salary: Int
public let workingDays: [Days]
public var boss: Person?
private enum CodingKeys: String, CodingKey {
case department
case dependents
case salary
case workingDays
case boss
}
required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
department = try container.decode(String.self, forKey: .department)
dependents = try container.decode([Person].self, forKey: .dependents)
salary = try container.decode(Int.self, forKey: .salary)
workingDays = try container.decode([Days].self, forKey: .workingDays)
boss = try container.decode(Person.self, forKey: .boss)
try super.init(from: decoder)
}
}
public class Boss: Employee {
let promotedAt: Double
let assistant: Employee?
enum CodingKeys: String, CodingKey {
case promotedAt
case assistant
}
required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
promotedAt = try container.decode(Double.self, forKey: .promotedAt)
assistant = try container.decodeIfPresent(Employee.self, forKey: .assistant)
try super.init(from: decoder)
}
}
For example in the following response, in the boss section, personType is set to 'Boss'. So it should be decoded to the Boss type. If it were 'Employee' it should automatically decode to Employee or if it null is should decode to 'Person'.
{ name: 'Shahid Khaliq',
age: 5147483645,
address: 'H # 531, S # 20',
uid: '123321',
salary: 20000,
department: 'Software Development',
workingDays: [ 'Monday', 'Tuesday', 'Friday' ],
boss:
{ personType: 'Boss',
assistant: null,
name: 'Zeeshan Ejaz',
age: 5147483645,
address: 'H # 531, S # 20',
uid: '123321',
birthday: '1994-02-13',
birthtime: '1994-02-13T14:01:54.000Z',
salary: 20000,
department: 'Software Development',
joiningDay: 'Saturday',
workingDays: [ 'Monday', 'Tuesday', 'Friday' ],
dependents: null,
hiredAt: 'Sun, 06 Nov 1994 08:49:37 GMT',
boss: null,
promotedAt: 1484719381 },
dependents: null,
hiredAt: 'Sun, 06 Nov 1994 08:49:37 GMT',
personType: null }

Answer 1

Need to change model as per current response you posted
public class Employee: Person {
public let department: String
public let dependents: [Person]?
public let salary: Int
public let workingDays:[String] //[Days]
public var boss: Person?
private enum CodingKeys: String, CodingKey {
case department
case dependents
case salary
case workingDays
case boss
}
required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
department = try container.decode(String.self, forKey: .department)
//dependents = try container.decode([Person].self, forKey: .dependents)
dependents = try container.decodeIfPresent([Person].self, forKey: .dependents)
salary = try container.decode(Int.self, forKey: .salary)
// workingDays = try container.decode([Days].self, forKey: .workingDays)
workingDays = try container.decode([String].self, forKey: .workingDays)
// boss = try container.decode(Person.self, forKey: .boss)
boss = try container.decodeIfPresent(Person.self, forKey: .boss)
try super.init(from: decoder)
}
}
here added decodeIfPresent in few properties as it null as per current response
while decoding you can use different thing, i have used SwiftJSON to make code more readable ,
// i have saved response in Response.JSON file so can change response as per need while testing below code.
let file = Bundle.main.path(forResource: "Response", ofType: "JSON")
let dataURL = URL(fileURLWithPath: file!)
let data = try! Data(contentsOf: dataURL)
let jsonData = try! JSON(data: data)
//here JSON is struct which is part of SwiftyJSON
print("jsondata \(jsonData)")
do {
let bossDict = jsonData["boss"]
let dataBoss : Data = try! bossDict.rawData()
let bossType = bossDict["personType"].string
if let type = bossType {
if type == "Boss"{
let bossObj = try! JSONDecoder().decode(Boss.self, from: dataBoss)
print("boss name \(String(describing: bossObj.name))")
bossObj.listPropertiesWithValues()
}else{
// type == "Employee"
let emplyeeObj = try! JSONDecoder().decode(Employee.self, from: dataBoss)
print("Employee name \(String(describing: emplyeeObj.name))")
emplyeeObj.listPropertiesWithValues()
}
}else{
//type = nil
}
}catch{
print("exception \(error)")
}
You can download working demo of the same at link
DemoCodable

Answer 2

I would add a switch statement at the end of the init(from decoder:) in the Employee class
switch personType {
case "Boss":
boss = try container.decode(Boss.self, forKey: .boss)
case "Employee":
boss = try container.decode(Employee.self, forKey: .boss)
default:
boss = nil
}