Swift Rest API Call with Codable returning array

Question

This is a further link on this question Swift Rest API call example using Codable

When I change the code to handle an array, I'm getting a JSON error. Here's what I'm doing. What am I doing wrong? It errors with "error with json".

// Transaction Class

import Foundation

final class Transaction: Codable {
    
    var id: Int?
    var date: Date
    var amount: Int
    var planeID: Int
    var userID: UUID
    var month: Int
    var year: Int

    
    init(date: Date, amount: Int, planeID: Int, userID: UUID, month: Int, year: Int) {
        self.date = date
        self.amount = amount
        self.planeID = planeID
        self.userID = userID
        self.month = month
        self.year = year
    }
}

// Call in my ViewController

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        
        getJson() { (json) in
            print(json.count)
            //print(json[0].note)
            print(json)
        }
    }
    
    func getJson(completion: @escaping ([Transaction])-> ()) {
        let urlString = "http://192.168.1.98:8080/admin/transactions"
        if let url = URL(string: urlString) {
        URLSession.shared.dataTask(with: url) {data, res, err in
            guard let data = data else {return print("error with data")}
            let decoder = JSONDecoder()
            guard let json = try? decoder.decode([Transaction].self, from: data) else {return print("error with json")}
            completion(json)
          }.resume()
        }
    }

}

And this is the JSON response body when I call in Rested

//Form of the JSON response body when I used call via Rested

[
    {
        "amount": 1000,
        "userID": "7698E011-6643-421E-A30D-121FF488FDBB",
        "id": 2,
        "month": 5,
        "date": "2021-01-14T20:30:31Z",
        "year": 2021,
        "planeID": 1
    },
    {
        "amount": 1000,
        "userID": "7698E011-6643-421E-A30D-121FF488FDBB",
        "id": 3,
        "month": 5,
        "date": "2021-01-14T20:30:31Z",
        "year": 2021,
        "planeID": 2
    },
    {
        "amount": 1000,
        "userID": "7698E011-6643-421E-A30D-121FF488FDBB",
        "id": 4,
        "month": 5,
        "date": "2021-01-14T20:30:31Z",
        "year": 2021,
        "planeID": 2
    },
    {
        "amount": 1000,
        "userID": "7698E011-6643-421E-A30D-121FF488FDBB",
        "id": 5,
        "month": 5,
        "date": "2021-01-14T20:30:31Z",
        "year": 2021,
        "planeID": 2
    },
    {
        "amount": 1000,
        "userID": "7698E011-6643-421E-A30D-121FF488FDBB",
        "id": 6,
        "month": 5,
        "date": "2021-01-14T20:30:31Z",
        "year": 2021,
        "planeID": 2
    }
]

Answer 1

If you use try/catch and print the error, you'd see that the error happens when decoding the date property. (as mentioned in comments, don't hide the error with try? - you won't know what went wrong)

To decode the date correctly into Date, you need to set a date decoding strategy on the decoder. In your case, the date appears to be a standard ISO8601, which is a built-in decoding strategy in JSONDecoder. So, all you need to do is just add one line:

let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .iso8601 // <-- ADD THIS

// use do/try/catch with decoding
do {
   let transactions = try decoder.decode([Transaction].self, from: data)
   completion(transactions)
} catch {
   print(error) // or handle it somehow
}