Decode JSON with Dynamic Keys using Decodable

decode.swift

// https://swiftsenpai.com/swift/decode-dynamic-keys-json/
// https://stackoverflow.com/questions/49549691/how-to-handle-dynamic-keys-from-json-response-using-swift-4-coding-keys

import Foundation

let json = """
{
    "name": "Avengers High",
    "students": {
        "S001": {
          "firstName": "Tony",
          "lastName": "Stark"
        },
        "S002": {
          "firstName": "Peter",
          "lastName": "Parker"
        },
        "S003": {
          "firstName": "Bruce",
          "lastName": "Wayne"
        }
    }
}
"""

let data = Data(json.utf8)

struct GenericCodingKeys: CodingKey {
    var stringValue: String
    var intValue: Int?
    
    init?(intValue: Int) {
        self.intValue = intValue
        self.stringValue = "\(intValue)"
    }
    
    init?(stringValue: String) {
        self.stringValue = stringValue
    }
}

struct Student: Decodable {
    let firstName: String
    let lastName: String
}

struct School: Decodable {
    let name: String
    var students: [Student]
    
    private enum CodingKeys: CodingKey {
        case name, students
    }
    
    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.name = try container.decode(String.self, forKey: .name)
        
        self.students = [Student]()
        let subContainer = try container.nestedContainer(keyedBy: GenericCodingKeys.self, forKey: .students)
        for key in subContainer.allKeys {
            let student = try subContainer.decode(Student.self, forKey: key)
            self.students.append(student)
        }
    }
}

let decodedResult = try! JSONDecoder().decode(School.self, from: data)
print(decodedResult.students[0])