Decode and Flatten JSON with Dynamic Keys Using Swift Decodable (https://swiftsenpai.com/swift/decode-dynamic-keys-json/)

Decode-Dynamic-Keys-JSON-Final.swift

import Foundation

let jsonString = """
{
  "S001": {
    "firstName": "Tony",
    "lastName": "Stark"
  },
  "S002": {
    "firstName": "Peter",
    "lastName": "Parker"
  },
  "S003": {
    "firstName": "Bruce",
    "lastName": "Wayne"
  }
}
"""

struct Student: Decodable {

    let firstName: String
    let lastName: String
    let studentId: String

    enum CodingKeys: CodingKey {
        case firstName
        case lastName
    }

    init(from decoder: Decoder) throws {

        let container = try decoder.container(keyedBy: CodingKeys.self)

        // Decode firstName & lastName
        firstName = try container.decode(String.self, forKey: CodingKeys.firstName)
        lastName = try container.decode(String.self, forKey: CodingKeys.lastName)

        // Extract studentId from coding path
        studentId = container.codingPath.first!.stringValue
    }
}

struct DecodedArray<T: Decodable>: Decodable {

    typealias DecodedArrayType = [T]

    private var array: DecodedArrayType

    // Define DynamicCodingKeys type needed for creating decoding container from JSONDecoder
    private struct DynamicCodingKeys: CodingKey {

        // Use for string-keyed dictionary
        var stringValue: String
        init?(stringValue: String) {
            self.stringValue = stringValue
        }

        // Use for integer-keyed dictionary
        var intValue: Int?
        init?(intValue: Int) {
            // We are not using this, thus just return nil
            return nil
        }
    }

    init(from decoder: Decoder) throws {

        // Create decoding container using DynamicCodingKeys
        // The container will contain all the JSON first level key
        let container = try decoder.container(keyedBy: DynamicCodingKeys.self)

        var tempArray = DecodedArrayType()

        // Loop through each keys in container
        for key in container.allKeys {

            // Decode T using key & keep decoded T object in tempArray
            let decodedObject = try container.decode(T.self, forKey: DynamicCodingKeys(stringValue: key.stringValue)!)
            tempArray.append(decodedObject)
        }

        // Finish decoding all T objects. Thus assign tempArray to array.
        array = tempArray
    }
}

// Transform DecodedArray into custom collection
extension DecodedArray: Collection {

    // Required nested types, that tell Swift what our collection contains
    typealias Index = DecodedArrayType.Index
    typealias Element = DecodedArrayType.Element

    // The upper and lower bounds of the collection, used in iterations
    var startIndex: Index { return array.startIndex }
    var endIndex: Index { return array.endIndex }

    // Required subscript, based on a dictionary index
    subscript(index: Index) -> Iterator.Element {
        get { return array[index] }
    }

    // Method that returns the next index when iterating
    func index(after i: Index) -> Index {
        return array.index(after: i)
    }
}


let jsonData = Data(jsonString.utf8)
// Decode JSON into [Student]
let decodedResult = try! JSONDecoder().decode(DecodedArray<Student>.self, from: jsonData)

Does this method work if the Student Type also contains an nested element? .. I've been trying to decode a JSON response where this is the case using your excellent tutorial, and as soon as I try to decode a nested element it fails to decode.

for example.. I might have a json response of different Schools, containing Classrooms, Teachers and where the Student name is the identifier, and each Student has a nested list of Books they carry..

your method works up to the point i try to decode the nested Books.. (although I might well be making an error somewhere)

Assuming this is the JSON you trying to decode:

{
  "S001": {
    "firstName": "Tony",
    "lastName": "Stark",
    "books": [
      {
        "name": "book1"
      },
      {
        "name": "book2"
      },
      {
        "name": "book3"
      }
    ]
  },
  "S002": {
    "firstName": "Peter",
    "lastName": "Parker",
    "books": []
  },
  "S003": {
    "firstName": "Bruce",
    "lastName": "Wayne",
    "books": []
  }
}

All you need to do is to create a new Book struct and update the Student struct accordingly:

struct Book: Decodable {
    let name: String
}

struct Student: Decodable {

    let firstName: String
    let lastName: String
    let studentId: String
    let books: [Book]

    enum CodingKeys: CodingKey {
        case firstName
        case lastName
        case books
    }

    init(from decoder: Decoder) throws {

        let container = try decoder.container(keyedBy: CodingKeys.self)

        // Decode firstName & lastName
        firstName = try container.decode(String.self, forKey: CodingKeys.firstName)
        lastName = try container.decode(String.self, forKey: CodingKeys.lastName)

        // Extract studentId from coding path
        studentId = container.codingPath.first!.stringValue
        
        // Decode books
        books = try container.decode([Book].self, forKey: CodingKeys.books)
    }
}

Lee: Thanks you very much! With this I can finally handle a JSON file which contains the following: let jsonString = """ { "events": { "141": { "name": "Ultrabar Fridays", "event_subtitle": "Each and every Friday party the night away at the hottest party in the city ", "learnmore_link": "https://www.eventbrite.com/e/ultrabar-fridays-tickets-53478213777", "image_url": "https://poshnights.com/wp-content/uploads/2021/12/141_image.jpg" }, "393": { "name": "Adult Paint and Play DC", "event_subtitle": "Come out and enjoy a wonderful evening of fun, paint, and cocktails", "learnmore_link": "https://www.eventbrite.com/e/adult-paint-and-play-dc-tickets-168964053031", "image_url": "https://poshnights.com/wp-content/uploads/2021/12/393_image.jpg" } } } “"" Your solution worked perfectly. Here is the result: ▿ __lldb_expr_160.DecodedArray ▿ array: 2 elements ▿ __lldb_expr_160.Event - name: "Adult Paint and Play DC" - event_subtitle: "Come out and enjoy a wonderful evening of fun, paint, and cocktails" - learnmore_link: "https://www.eventbrite.com/e/adult-paint-and-play-dc-tickets-168964053031" - image_url: "https://poshnights.com/wp-content/uploads/2021/12/393_image.jpg" ▿ __lldb_expr_160.Event - name: "Ultrabar Fridays" - event_subtitle: "Each and every Friday party the night away at the hottest party in the city " - learnmore_link: "https://www.eventbrite.com/e/ultrabar-fridays-tickets-53478213777" - image_url: "https://poshnights.com/wp-content/uploads/2021/12/141_image.jpg” Again, many thanks. If you have a Patreon account, let me know and I will make a contribution. Charlie

…

On Apr 17, 2022, at 5:53 AM, Lee Kah Seng ***@***.***> wrote: @LeeKahSeng commented on this gist. let jsonString = """ { "students': { "S001": { "firstName": "Tony", "lastName": "Stark" }, "S002": { "firstName": "Peter", "lastName": "Parker" }, "S003": { "firstName": "Bruce", "lastName": "Wayne" } } } any idea how to handle this structure?????? It is fairly straightforward, all you need to do is to create another data type to hold the student array. Here's how: struct MyData: Decodable { let students: DecodedArray<Student> } let jsonData = Data(jsonString.utf8) let decodedResult = try! JSONDecoder().decode(MyData.self, from: jsonData) print(decodedResult.students) — Reply to this email directly, view it on GitHub <https://gist.github.com/ceb374a8f297e0b5982f926f6b43ea12#gistcomment-4135482>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AB2C6PFYH6PWVF33K5VQ5C3VFPNRBANCNFSM5TO42KGQ>. You are receiving this because you commented.

In extension DecodedArray: Collection the correct associated type for a collection's iterator element is Element, not Iterator.Element.

    // Required subscript, based on a dictionary index
    subscript(index: Index) -> Element {
        get { return array[index] }
    }

{
  "EventName": "broadcast-price",
  "EventData": {
    "data": {
      "XRPUSDT": {
        "change24h": 0.27,
        "change7d": 10.89,
        "exchange": "bsc",
        "icon": "",
        "id": "",
        "isDown": false,
        "isUp": true,
        "max24h": 0,
        "min24h": 0,
        "name": "",
        "pair": "",
        "price": 0.5245,
        "symbol": "XRPUSDT",
        "timeStamp": "2023-06-04T07:41:57.29489505Z",
        "volume_24h": 71163040.90439999,
        "volume_24h_origin": 0
      },
      "exchange": "bsc",
      "token": "XRPUSDT"
    },
    "event": "symbol-data"
  }
}

How about for single object sir? @LeeKahSeng Thanks!