SOLVED: Decoding JSON

@erenfra HWS+

Feb '23

Hi community,

Sorry for the basic question, but since yesterday I am not able to decode this JSON data. I have implemented the Bundle-Decodable from the Moonshot project.

Getting this error: Fatal error: Failed to decode scales.json from bundle.

[
    {
        "id": "pA",
        "scales": [
            {
                "activity" : "Legato Pentascales",
                "key": "C, G, D, Am",
                "played": "Hands Separated",
                "playedDesc": "Tonic to dominat, ascending and descending, ending with solid root-position triad",
                "tempoValue": "100",
                "noteValue:": "quarter"
            },
            {
                "activity" : "Staccato Pentascales",
                "key": "C, G, D, Am",
                "played": "Hands Separated",
                "playedDesc": "Tonic to dominat, ascending and descending, ending with solid root-position triad",
                "tempoValue": "100",
                "noteValue:": "quarter-staccato"
            }
        ]
    },
    {
        "id": "pB",
        "scales": [
            {
                "activity" : "Legato Pentascales",
                "key": "D, A, F, Em, Dm",
                "played": "Hands Separated",
                "playedDesc": "Tonic to dominat, ascending and descending, ending with solid root-position triad",
                "tempoValue": "60",
                "noteValue:": "2-eighth"
            },
            {
                "activity" : "Staccato Pentascales",
                "key": "D, A, F, Em, Dm",
                "played": "Hands Separated",
                "playedDesc": "Tonic to dominat, ascending and descending, ending with solid root-position triad",
                "tempoValue": "60",
                "noteValue:": "2-eighth-staccato"
            },
            {
                "activity" : "One-octave Scales",
                "key": "C, G, Am (natural)",
                "played": "Hands Separated",
                "playedDesc": "One-octave",
                "tempoValue": "60",
                "noteValue:": "2-eighth"
            },
            {
                "activity" : "Contrary Motion Scale",
                "key": "C",
                "played": "Hands Together",
                "playedDesc": "One-octave",
                "tempoValue": "60",
                "noteValue:": "2-eighth"
            }
        ]
    }

]

This is my struct:

import Foundation

struct TechRequirements: Codable, Identifiable  {

    let id: String
    let scales: [Scale]

}

struct Scale: Codable {

    let activity: String
    let key: String
    let played: String
    let playedDesc: String
    let tempoValue: String
    let noteValue: String

}

Bundle-Decodable:

import Foundation

extension Bundle {
    func decode<T: Codable>(_ file: String) -> T {
        guard let url = self.url(forResource: file, withExtension: nil) else {
            fatalError("Failed to locate \(file) in bundle.")
        }

        guard let data = try? Data(contentsOf: url) else {
            fatalError("Failed to load \(file) from bundle.")
        }

        let decoder = JSONDecoder()

        guard let loaded = try? decoder.decode(T.self, from: data) else {
            fatalError("Failed to decode \(file) from bundle.")
        }

        return loaded
    }
}

My DataManager:

import Foundation

class DataManager: ObservableObject {

    @Published var scales: [TechRequirements] = Bundle.main.decode("scales.json")

}

Thanks for the support. Renato.

@roosterboy HWS+

Feb '23

Instead of this:

guard let loaded = try? decoder.decode(T.self, from: data) else {
    fatalError("Failed to decode \(file) from bundle.")
}

return loaded

give yourself a chance to see what the error is:

do {
    let loaded = try decoder.decode(T.self, from: data)
    return loaded
} catch {
    fatalError("\(error)")
}

and see what gets printed to the console.

If you search around here on the forums, you can even find other ways of doing a similar thing that give you a prettier, more user-friendly error description, but I find the above works well enough.

For this particular case, I would suggest taking a closer look at your JSON keys compared to the corresponding property names in your structs.

@erenfra HWS+

Feb '23

Thanks for the code and help. I found the error on the noteValue key. There was a ":" inside.

Here is the error message.:

2023-02-09 22:02:02.834915-0600 Syllabus[6840:6509202] Syllabus/Bundle-Decodable.swift:33: Fatal error: keyNotFound(CodingKeys(stringValue: "noteValue", intValue: nil), Swift.DecodingError.Context(codingPath: [_JSONKey(stringValue: "Index 0", intValue: 0), CodingKeys(stringValue: "scales", intValue: nil), _JSONKey(stringValue: "Index 0", intValue: 0)], debugDescription: "No value associated with key CodingKeys(stringValue: \"noteValue\", intValue: nil) (\"noteValue\").", underlyingError: nil))

Thanks again, Renato.

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