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SOLVED: Having issues decoding JSON, help needed

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Hi, I've been wrestling with this problem for a few hours and can't seem to find the issue (although I suspect it is with the JSON itself as I created the file).

I am trying to create a simple quiz type app for Fantasy Premier League players. I have created the list of questions as a JSON here...

[
{
        "id": 1,
        "question": "Budget midfielders and forwards (costing around £6.0m) tend to provide worse value than defenders at the same price",
        "category": "bravo"
    },

{
        "id": 2,
        "question": "The best way to spend transfers is on buying the best captain option for each gameweek",
        "category": "romeo"
    },

{
        "id": 3,
        "question": "I spend a lot of transfers trying to get the best budget midfielders and forwards (costing around £6.0m)",
        "category": "yankee"
    },

{
        "id": 4,
        "question": "I strive to be a very patient manager",
        "category": "bravo"
    },

{
        "id": 5,
        "question": "I rarely captain fixture-proof players, but prefer to captain flat-track bullies",
        "category": "romeo"
    },

{
        "id": 6,
        "question": "I like to stay close to the template of top managers",
        "category": "yankee"
    },

{
        "id": 7,
        "question": "I always pay a lot of attention to which players provide the highest points per million",
        "category": "bravo"
    },

{
        "id": 8,
        "question": "I am willing to own players who are not nailed if they are very explosive.",
        "category": "romeo"
    },

{
        "id": 9,
        "question": "I usually prefer to “set and forget” my premium midfielders and forwards",
        "category": "yankee"
    },

{
        "id": 10,
        "question": "I frequently play formations with more than three defenders",
        "category": "bravo"
    },

{
        "id": 11,
        "question": "I usually prefer not to captain the same player that the majority of managers are captaining",
        "category": "romeo"
    },

{
        "id": 12,
        "question": "I start the season with a flexible team where it is easy to get any emerging player into my team",
        "category": "yankee"
    },

{
        "id": 13,
        "question": "I spend a high percentage of my budget on defenders",
        "category": "bravo"
    },

{
        "id": 14,
        "question": "I am willing to take hits for moves that have high potential upside",
        "category": "romeo"
    },

{
        "id": 15,
        "question": "I am confident that if I make good transfers, my budget midfielders and forwards will outscore defenders at a similar price",
        "category": "yankee"
    },

{
        "id": 16,
        "question": "I like owning consistent players, even if most managers consider them boring",
        "category": "bravo"
    },

{
        "id": 17,
        "question": "I am not very concerned if I lose team value by transferring heavy hitters in and out of my team",
        "category": "romeo"
    },

{
        "id": 18,
        "question": "Players that start the season in my team are often nothing more than placeholders for the best emerging option",
        "category": "yankee"
    },

{
        "id": 19,
        "question": "I am willing to stubbornly ignore bandwagons for players I do not trust",
        "category": "bravo"
    },

{
        "id": 20,
        "question": "Taking big risks is essential to achieving my FPL goals",
        "category": "romeo"
    },

{
        "id": 21,
        "question": "I prefer to spread my risk by rarely doubling or tripling up on any team’s attack or defence",
        "category": "yankee"
    },

{
        "id": 22,
        "question": "I usually spread my budget fairly evenly around my team rather than owning more premium midfielders and forwards",
        "category": "bravo"
    },

{
        "id": 23,
        "question": "I often like to own three attacking assets from the same team",
        "category": "romeo"
    },

{
        "id": 24,
        "question": "If there is a clear consensus among top managers on the best captain choice, it is a bad time to choose a different captain",
        "category": "yankee"
    },

{
        "id": 25,
        "question": "I am comfortable owning only one or two captain options at a time",
        "category": "bravo"
    },

{
        "id": 26,
        "question": "I dislike “coverage” picks and don’t mind being without an attacking asset from one top team to spend more money on a different team",
        "category": "romeo"
    },

{
        "id": 27,
        "question": "To the extent possible, I like to own all the highly owned premium midfielders and forwards",
        "category": "yankee"
    },

{
        "id": 28,
        "question": "I try to focus my transfers on removing the weakest link, more than on the players I’m getting in",
        "category": "bravo"
    },

{
        "id": 29,
        "question": "Spending transfers on defenders is usually wasteful",
        "category": "romeo"
    },

{
        "id": 30,
        "question": "It’s a myth that you need differentials to climb the ranks",
        "category": "yankee"
    }
]

When I try to decode using this code..

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
    }
}

I get the error "Fatal error: Failed to decode Questions.json from bundle".

Is anyone able to assist in what may be the issue please? Thanks in advance

1      

hi,

you'll need to show how you call the extension on Bundle to load the JSON. you probably are using the wrong type there, because the JSON looks OK if you're using a struct like this:

struct MyType: Codable {
    let id: Int
    let question: String
    let category: String
}

hope that helps,

DMG

1      

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

Don't do this, use proper error handling. That try? turns any error that occurs into a nil and so hides the error from you.

Do something like this instead:

do {
    let loaded = decoder.decode(T.self, from: data)
    return loaded
} catch {
    print(error)
    fatalError("Failed to decode \(file) from bundle.")
}

Then you can see what your error is.

1      

I had to add try to the do catch block to get it to work in mine

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

1      

Whoops, yeah, that's required. Must have deleted too much when I got rid of the ?

1      

Hi Paul uses this as abridge version so @roosterboy correct in saying that you should use do, try, catch. This is Paul full version and I save it as a code snippet so when he does this I will just use this full version.

extension Bundle {
    func decode<T: Decodable>(
        _ type: T.Type,
        from file: String,
        dateDecodingStrategy: JSONDecoder.DateDecodingStrategy = .deferredToDate,
        keyDecodingStrategy: JSONDecoder.KeyDecodingStrategy = .useDefaultKeys
    ) -> 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()
        decoder.dateDecodingStrategy = dateDecodingStrategy
        decoder.keyDecodingStrategy = keyDecodingStrategy

        // swiftlint:disable line_length
        do {
            return try decoder.decode(T.self, from: data)
        } catch DecodingError.keyNotFound(let key, let context) {
            fatalError("Failed to decode \(file) from bundle due to missing key '\(key.stringValue)' - \(context.debugDescription)")
        } catch DecodingError.typeMismatch(_, let context) {
            fatalError("Failed to decode \(file) from bundle due to type mismatch - \(context.debugDescription)")
        } catch DecodingError.valueNotFound(let type, let context) {
            fatalError("Failed to decode \(file) from bundle due to missing \(type) value = \(context.debugDescription)")
        } catch DecodingError.dataCorrupted(_) {
            fatalError("Failed to decode \(file) from bundle because it appears to be invalid JSON.")
        } catch {
            fatalError("Failed to decode \(file) from bundle: \(error.localizedDescription)")
        }
    }
}

You need to make sure that your Model is correct I use Ducky to make sure

struct Question: Codable, Identifiable {
  let id: Int
  let question: String
  let category: String
}

Then when you call from JSON use this

let questions = Bundle.main.decode([Question].self, from: "JSONname.json")

PS This also allow to change dateDecodingStrategy and keyDecodingStrategy from call if the JSON requires it.

let questions = Bundle.main.decode([Question].self, from: "JSONname.json", dateDecodingStrategy: .iso8601, keyDecodingStrategy: .convertFromSnakeCase)

2      

Thank you, I replaced my code for yours @NigelGee and it is now working.

I think the cause of the issue was that I was using

let questions : [String: Question] =
    Bundle.main.decode("Questions.json")

But replacing with

let questions = Bundle.main.decode([Question].self, from: "Questions.json")

Has resolved.

Thanks for your help

1      

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