Decode JSON Swift 4

Question

Can someone tell what is wrong with the code? I'm trying to parse the JSON from the server into variables to store the values. When i'm running the code, i'm not getting any errors. When i'm doing the print(users) after decoding the data, it's not returning anything. Can someone help me with this issue?

This is the code i'm using to retrieve the data from the server.

guard let url = URL(string: "my-url") else { return }
        let session = URLSession.shared
        let task = session.dataTask(with: url) { (data, _, _) in
            guard let data = data else { return }


            do {

                let user = try JSONDecoder().decode(User.self, from: data)
                print(user)

            } catch {}
        }
        task.resume()

JSON result from the server

{
"UserId": "55844ef7-3f05-4560-8b37-216df422ffb8",
"ContactsDto": [
    {
        "Id": null,
        "UserId": null,
        "FriendUserId": "e61d09f8-9aec-4035-b0be-c36abea2d82b",
        "FirstName": null,
        "LastName": null,
        "Email": "",
        "PhonePrefix": null,
        "Phone": "54943597",
        "InviteStatus": "pending",
        "UserStatus": null,
        "ErrorCode": 0,
        "ErrorMessage": null
    },
    {
        "Id": null,
        "UserId": null,
        "FriendUserId": "b2e0d6d7-d97c-475e-a2ab-71cb8091a7a0",
        "FirstName": null,
        "LastName": null,
        "Email": "",
        "PhonePrefix": null,
        "Phone": "207-7575",
        "InviteStatus": "pending",
        "UserStatus": null,
        "ErrorCode": 0,
        "ErrorMessage": null
    },
    {
        "Id": null,
        "UserId": null,
        "FriendUserId": "8f8d6061-3a69-4641-ac40-329a824ff4e1",
        "FirstName": null,
        "LastName": null,
        "Email": "",
        "PhonePrefix": null,
        "Phone": "58511968",
        "InviteStatus": "pending",
        "UserStatus": null,
        "ErrorCode": 0,
        "ErrorMessage": null
    },
    {
        "Id": null,
        "UserId": null,
        "FriendUserId": "40c1e461-eb98-4e18-9363-13cfa460fe7e",
        "FirstName": null,
        "LastName": null,
        "Email": "",
        "PhonePrefix": null,
        "Phone": "57864550",
        "InviteStatus": "accepted",
        "UserStatus": null,
        "ErrorCode": 0,
        "ErrorMessage": null
    }
],
"ErrorCode": 0,
"ErrorMessage": null

}

My Structure

struct User: Decodable {

let UserId: String?
let ContactsDto: [ContactsDto]?
let ErrorCode: Int?
let ErrorMessage: String?

}

struct ContactsDto : Decodable {

let Id : String?
let UserId : String?
let FriendUserId : String?
let FirstName : String?
let LastName : String?
let Email : String?
let PhonePrefix : String?
let Phone : String?
let InviteStatus : String?
let UserStatus : String?
let ErrorCode : String?
let ErrorMessage : String?

}

Answer 1

From looking at your code, the way you are trying to decode the JSON isn't correct.

You aren't returning an array of User, but a single User Object.

As such you could try the following:

let user = try! JSONDecoder().decode(User.self, from: data)

Answer 2

Based on your errors and as Josh told you in the comments, the types on your model are not correct.

For example, one of your ContactDto object is this:

{
    "Id": null,
    "UserId": null,
    "FriendUserId": "e61d09f8-9aec-4035-b0be-c36abea2d82b",
    "FirstName": null,
    "LastName": null,
    "Email": "",
    "PhonePrefix": null,
    "Phone": "54943597",
    "InviteStatus": "pending",
    "UserStatus": null,
    "ErrorCode": 0,
    "ErrorMessage": null
},

The ErrorCode type is a number (it looks like an integer), but in your model struct is a String?.

Please check every field to get all types, then fix the model and try again.