Decoding Error -- Expected to decode Dictionary but found an array instead

Question

I am new to swift programming and Xcode and am try to call mysql data from the database to Xcode using Json encoding. I was able to successfully call all the data (array) but when I decide to call only one value(column) say Courses.name I get the "Decoding Error -- Expected to decode Dictionary but found an array instead." How do I work my way around this problem? My goal is to print only courses.name

import UIKit

struct Course: Decodable {
let id: String
let name: String
let member:  String

 }

class ViewController: UIViewController {

override func viewDidLoad() {
    super.viewDidLoad()

    let jsonUrlString = "http://oriri.ng/aapl/service.php"
    guard let url = URL(string: jsonUrlString) else
    { return }

    URLSession.shared.dataTask(with: url) { (data, response, err) in

        guard let data =  data else{ return }

        do {

            let courses = try JSONDecoder().decode(Course.self, from: data)
            print(courses.name)


        } catch let jsonErr {
            print("Error serializing json:", jsonErr)
        }

    }.resume()

   }
}

Fabian · Accepted Answer · 2018-08-15T21:31:24.740

32

[{"id":"1","name":"sobande_ibukun","member":"blue"}]

The [] around denotes that it is an array. Decode with the following and it should work:

let courses = try JSONDecoder().decode([Course].self, from: data)

If you are sure that it will always be one course you can do:

print(courses.first!.name)

If there may be many courses you can print every name:

courses.forEach { course in print(course.name) }

edited Aug 15 '18 at 21:31

answered Aug 15 '18 at 21:24

Fabian

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Thank you, but I get another error "Value of type '[Course]' has no member 'name'" and it fails to build – Jamiu Momoh Aug 15 '18 at 21:29
@JamiuMomoh Updated the answer to reflect that. An array of courses has elements. You have to access a specific element in the array to call `.name` on it. – Fabian Aug 15 '18 at 21:32
Yes! it will always be one course as I will restrict the result with mysql statement. Thank you so much, being trying to wrap my head around it for hours.Works as intended. – Jamiu Momoh Aug 15 '18 at 21:36
Not working. get error: error: cannot convert value of type '[Course.Type]' to expected argument type 'T.Type' – ArgaPK Jul 07 '21 at 05:58
Thanks, I am very new to Swift and I tried putting the [] in all the wrong places before I got this answer – Sudhir Kesharwani May 02 '23 at 07:12

score 0 · Answer 2 · edited Jan 11 '23 at 00:04

Just wanted to add to Fabians response above.

The fix for showing all of them is to have a struct with each of your keys (in the array) like so:

struct Advisor_Info: Decodable {
    let advisor_email: String
    let advisor_firstname: String
    let advisor_lastname: String
    let advisor_phonenumber: String
}

Then extract your items from the JSON dictionary string like so:

    do {        
        let decodedResponse = try JSONDecoder().decode([Advisor_Info].self, from: data)
        print(decodedResponse as Any)
        for each in decodedResponse {
            print(each)
            print(each.advisor_email)
        }
        
    } catch DecodingError.dataCorrupted(let context) {
        print(context)
    } catch DecodingError.keyNotFound(let key, let context) {
        print("Key '\(key)' not found:", context.debugDescription)
        print("codingPath:", context.codingPath)
    } catch DecodingError.valueNotFound(let value, let context) {
        print("Value '\(value)' not found:", context.debugDescription)
        print("codingPath:", context.codingPath)
    } catch DecodingError.typeMismatch(let type, let context) {
        print("Type '\(type)' mismatch:", context.debugDescription)
        print("codingPath:", context.codingPath)
    } catch {
        print("error: ", error)
    }
}

Decoding Error -- Expected to decode Dictionary but found an array instead

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