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SOLVED: Why can't I parse this JSON data? Error: "Couldn't parse *.json as Array<Competition>"

Forums > SwiftUI
@benfrain  

I am a complete SwiftUI beginner. I have gone through Apple's Landmarks tutorial, and a bunch of the videos here. I am now trying to render out a view with some alternative JSON as the data.

However, when I try and use that data I get a Fatal Error in ModelData.swift - crashed due to fatalError in ModelData.swift at line 40

The logs don't show me anything I understand, they don't even reference that same message so I am lost.

I thought it must be something to do with how I have mapped the data. Here is my mapping of the JSON called Competition.swift, followed by the JSON, followed by my simple view.

Hope somebody can shed some light on what I have wrong here?

import Foundation
import SwiftUI

struct Competition: Codable, Identifiable {
    var id: UUID
    var _id: String
    var title: String
    var titleShort: String
    var classification: Classification
    var fixtures: [FixtureSingle]
    struct Classification: Codable {
        var title: String
        var bId: Int
    }
    struct FixtureSingle: Codable {
        var _id: String
        var title: String
        var date: String
        var venue: String
        var classification: Classification
        var competition: Competition
        var referee: Referee
        var participants: [Participant]
        var previousMeetings: PreviousMeeting
    }
    struct Referee: Codable {
        var titleShort: String
        var nationality: String
        var title: String
    }
    struct Participant: Codable {
        var titleShort: String
        var title: String
        var _id: String
        var kits: [Kit]
        var logo: String
        var nationality: String
        var preMatchStats: PreMatchStat
        var classification: Classification
        var form: [Form]
    }
    struct Kit: Codable {
        var asset: String
        var mainColour: String
    }
    struct PreMatchStat: Codable {
        var leadingScorer: LeadingScorer
        var leaguePosition: Int
        var cleanSheets: Double
        var atLeastOneGoal: Double
        var goalsScoredAverage: Double
        var goalsConcededAverage: Double
        var goalDifference: Int
        var winPercentage: Double
    }
    struct LeadingScorer: Codable {
        var totalGoals: Int
        var title: String
        var titleShort: String
    }
    struct Form: Codable {
        var date: String
        var titleShort: String
        var scoreline: [String]
        var winner: Int
        var participants: [FormParticipant]
    }
    struct FormParticipant: Codable {
        var _id: String
    }
    struct PreviousMeeting: Codable {
        var titleShort: String
        var winner: Int
        var date: Date
        var scoreline: [String]
        var competition: Competition
        var participants: [Participant]
    }

}

And here is the JSON file:

[{
"_id": "6304f394d05afb456f03d654",
      "title": "England Premier League",
      "titleShort": "EPL",
      "classification": {
        "title": "Soccer",
        "bId": 1
      },
      "fixtures": [
        {
          "_id": "6304f394d05afb456f03d656",
          "title": "Tottenham v Wolverhampton",
          "date": "Sat Aug 20 2022 12:30:00 GMT+0100 (British Summer Time)",
          "venue": "Tottenham Hotspur Stadium",
          "classification": {
            "bId": 1,
            "title": "Soccer"
          },
          "competition": {
            "_id": "6304f394d05afb456f03d654",
            "title": "England Premier League"
          },
          "referee": {
            "titleShort": "S Hooper",
            "nationality": "England",
            "title": "Simon Hooper"
          },
          "participants": [
            {
              "titleShort": "TOT",
              "title": "Tottenham",
              "_id": "6304f392d05afb456f03285d",
              "kits": [
                {
                  "asset": "Tottenham_Hotspur_Home_23",
                  "mainColour": "#ffffff"
                }
              ],
              "preMatchStats": {
                "leadingScorer": {
                  "totalGoals": 4,
                  "title": "Harry Kane",
                  "titleShort": "H Kane"
                },
                "leaguePosition": 4,
                "cleanSheets": 0.71,
                "atLeastOneGoal": 0.75,
                "goalsScoredAverage": 2.29,
                "goalsConcededAverage": 1.11,
                "goalDifference": 33,
                "winPercentage": 14.29
              },
              "classification": {
                "bId": 1
              },
              "form": [
                {
                  "date": "Sun Aug 14 2022 16:30:00 GMT+0100 (British Summer Time)",
                  "titleShort": "CHE v TOT",
                  "scoreline": [
                    "2-2"
                  ],
                  "winner": -1,
                  "participants": [
                    {
                      "_id": "6304f392d05afb456f032a72"
                    },
                    {
                      "_id": "6304f392d05afb456f03285d"
                    }
                  ]
                }

              ]
            },
            {
              "titleShort": "WOL",
              "title": "Wolverhampton",
              "_id": "6304f392d05afb456f032886",
              "kits": [
                {
                  "asset": "Wolverhampton_Wanderers_Home_23",
                  "mainColour": "#fecd32"
                }
              ],
              "preMatchStats": {
                "leadingScorer": {
                  "totalGoals": 3,
                  "title": "Daniel Podence",
                  "titleShort": "D Podence"
                },
                "leaguePosition": 14,
                "cleanSheets": 0.72,
                "atLeastOneGoal": 0.72,
                "goalsScoredAverage": 1.34,
                "goalsConcededAverage": 1.24,
                "goalDifference": 3,
                "winPercentage": 17.24
              },
              "classification": {
                "bId": 1
              },
              "form": [
                {
                  "date": "Sat Aug 13 2022 15:00:00 GMT+0100 (British Summer Time)",
                  "titleShort": "WOL v FUL",
                  "scoreline": [
                    "0-0"
                  ],
                  "winner": -1,
                  "participants": [
                    {
                      "_id": "6304f392d05afb456f032886"
                    },
                    {
                      "_id": "6304f392d05afb456f032953"
                    }
                  ]
                },
              ]
            }
          ],
          "previousMeetings": [
            {
              "titleShort": "TOT v WOL",
              "winner": 1,
              "date": "Sun Feb 13 2022 14:00:00 GMT+0000 (Greenwich Mean Time)",
              "scoreline": [
                "0-2"
              ],
              "competition": {
                "titleShort": "EPL"
              },
              "participants": [
                {
                  "titleShort": "TOT",
                  "_id": "6304f392d05afb456f03285d"
                },
                {
                  "titleShort": "WOL",
                  "_id": "6304f392d05afb456f032886"
                }
              ]
            },
            {
              "titleShort": "WOL v TOT",
              "winner": 1,
              "date": "Wed Sep 22 2021 19:45:00 GMT+0100 (British Summer Time)",
              "scoreline": [
                "2-2"
              ],
              "competition": {
                "titleShort": "EFL"
              },
              "participants": [
                {
                  "titleShort": "WOL",
                  "_id": "6304f392d05afb456f032886"
                },
                {
                  "titleShort": "TOT",
                  "_id": "6304f392d05afb456f03285d"
                }
              ]
            },
            {
              "titleShort": "WOL v TOT",
              "winner": 1,
              "date": "Sun Aug 22 2021 14:00:00 GMT+0100 (British Summer Time)",
              "scoreline": [
                "0-1"
              ],
              "competition": {
                "titleShort": "EPL"
              },
              "participants": [
                {
                  "titleShort": "WOL",
                  "_id": "6304f392d05afb456f032886"
                },
                {
                  "titleShort": "TOT",
                  "_id": "6304f392d05afb456f03285d"
                }
              ]
            },
            {
              "titleShort": "TOT v WOL",
              "winner": 0,
              "date": "Sun May 16 2021 14:05:00 GMT+0100 (British Summer Time)",
              "scoreline": [
                "2-0"
              ],
              "competition": {
                "titleShort": "EPL"
              },
              "participants": [
                {
                  "titleShort": "TOT",
                  "_id": "6304f392d05afb456f03285d"
                },
                {
                  "titleShort": "WOL",
                  "_id": "6304f392d05afb456f032886"
                }
              ]
            },
            {
              "titleShort": "WOL v TOT",
              "winner": -1,
              "date": "Sun Dec 27 2020 19:15:00 GMT+0000 (Greenwich Mean Time)",
              "scoreline": [
                "1-1"
              ],
              "competition": {
                "titleShort": "EPL"
              },
              "participants": [
                {
                  "titleShort": "WOL",
                  "_id": "6304f392d05afb456f032886"
                },
                {
                  "titleShort": "TOT",
                  "_id": "6304f392d05afb456f03285d"
                }
              ]
            }
          ]
        }
      ]
}]

And here is the view that won't load/preview:

import SwiftUI

struct FixtureList: View {
    @Environment(ModelData.self) var modelData
    var body: some View {
        Text("hello")
    }
}

#Preview {
    FixtureList().environment(ModelData())
}

2      

@Hatsushira  HWS+

Don't throw a FatalError when decoding but catch the error.

Here you find an example how to catch the error when decoding a json. This gives you a hint where to look.

2      

@NigelGee  HWS+

It maybe because you added

var id: UUID

Try changing to this

var id: UUID { UUID() }

2      

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@benfrain  

@NigelGee sadly that made no difference. Will likely just strip my model and data right back and try adding them in one by one.

@Hatsushira - I've added a print(error) in above my catch but it my model data, is there something else I should be be doing?

Here is the modelData:

import Foundation

@Observable
class ModelData {
    var competition: [Competition] = load("fixtures-pre-soccer-premier-league.json")

    var categories: [String: [Competition]] {
        Dictionary(
            grouping: competition,
            by: {$0.title}
        )
    }
}

func load<T: Decodable>(_ filename: String) -> T {
    let data: Data

    guard let file = Bundle.main.url(forResource: filename, withExtension: nil)
        else {
            fatalError("Couldn't find \(filename) in main bundle.")
    }

    do {
        data = try Data(contentsOf: file)
    } catch {
        fatalError("Couldn't load \(filename) from main bundle:\n\(error)")
    }

    do {
        let decoder = JSONDecoder()
        return try decoder.decode(T.self, from: data)
    } catch {
        print(error)
        fatalError("Couldn't parse \(filename) as \(T.self):\n\(error)")
    }
}

2      

@Hatsushira  HWS+

You want to know exactly as possible where the error is:

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)' not found – \(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)")
    }

2      

@NigelGee  HWS+

Hi @benfrain I added your json files to my project and add this decoder

extension Bundle {
    func decode<T: Decodable>(
        _ type: T.Type = T.self,
        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)")
        }
    }
}

Then added this model

struct Competition: Codable, Identifiable {
    var id: UUID { UUID() }
    var _id: String
    var title: String
    var titleShort: String
    var classification: Classification
    var fixtures: [Fixture]

    struct Classification: Codable {
        var title: String
        var bId: Int
    }

    struct Fixture: Codable {
        struct Classification: Codable {
            var bId: Int
            var title: String
        }

        struct Competition: Codable {
            var _id: String
            var title: String
        }

        struct Referee: Codable {
            var titleShort: String
            var nationality: String
            var title: String
        }

        struct Participant: Codable {
            struct Kit: Codable {
                var asset: String
                var mainColour: String
            }

            struct PreMatchStat: Codable {
                struct LeadingScorer: Codable {
                    var totalGoals: Int
                    var title: String
                    var titleShort: String
                }

                var leadingScorer: LeadingScorer
                var leaguePosition: Int
                var cleanSheets: Double
                var atLeastOneGoal: Double
                var goalsScoredAverage: Double
                var goalsConcededAverage: Double
                var goalDifference: Int
                var winPercentage: Double
            }

            struct Classification: Codable {
                var bId: Int
            }

            struct Form: Codable {
                struct Participant: Codable {
                    var _id: String
                }

                var date: String
                var titleShort: String
                var scoreline: [String]
                var winner: Int
                var participants: [Participant]
            }

            var titleShort: String
            var title: String
            var _id: String
            var kits: [Kit]
            var preMatchStats: PreMatchStat
            var classification: Classification
            var form: [Form]
        }

        struct PreviousMeeting: Codable {
            struct Competition: Codable {
                var titleShort: String
            }

            struct Participant: Codable {
                var titleShort: String
                var _id: String
            }

            var titleShort: String
            var winner: Int
            var date: String
            var scoreline: [String]
            var competition: Competition
            var participants: [Participant]
        }

        var _id: String
        var title: String
        var date: String
        var venue: String
        var classification: Classification
        var competition: Competition
        var referee: Referee
        var participants: [Participant]
        var previousMeetings: [PreviousMeeting]
    }
}

Then created this in ContentView

struct ContentView: View {
    let competitions = Bundle.main.decode([Competition].self, from: "Competition.json")

    var body: some View {
        List(competitions) {
            Text($0.title)
        }
    }
}

Showed in preview

English Premier League

So worked fine You may have trouble with _id as even though snake case will not decode as such (unless you use CodingKey) So the model would look like this and will work without `id: UUID { UUID() }

struct Competition: Codable, Identifiable {
    var id: String
    var title: String
    var titleShort: String
    var classification: Classification
    var fixtures: [Fixture]

    private enum CodingKeys: String, CodingKey {
        case id = "_id"
        case title
        case titleShort
        case classification
        case fixtures
    }

    struct Classification: Codable {
        var title: String
        var bID: Int

        private enum CodingKeys: String, CodingKey {
            case title
            case bID = "bId"
        }
    }

    struct Fixture: Codable {
        struct Classification: Codable {
            var bID: Int
            var title: String

            private enum CodingKeys: String, CodingKey {
                case bID = "bId"
                case title
            }
        }

        struct Competition: Codable {
            var id: String
            var title: String

            private enum CodingKeys: String, CodingKey {
                case id = "_id"
                case title
            }
        }

        struct Referee: Codable {
            var titleShort: String
            var nationality: String
            var title: String
        }

        struct Participant: Codable {
            struct Kit: Codable {
                var asset: String
                var mainColour: String
            }

            struct PreMatchStat: Codable {
                struct LeadingScorer: Codable {
                    var totalGoals: Int
                    var title: String
                    var titleShort: String
                }

                var leadingScorer: LeadingScorer
                var leaguePosition: Int
                var cleanSheets: Double
                var atLeastOneGoal: Double
                var goalsScoredAverage: Double
                var goalsConcededAverage: Double
                var goalDifference: Int
                var winPercentage: Double
            }

            struct Classification: Codable {
                var bID: Int

                private enum CodingKeys: String, CodingKey {
                    case bID = "bId"
                }
            }

            struct Form: Codable {
                struct Participant: Codable {
                    var id: String

                    private enum CodingKeys: String, CodingKey {
                        case id = "_id"
                    }
                }

                var date: String
                var titleShort: String
                var scoreline: [String]
                var winner: Int
                var participants: [Participant]
            }

            var titleShort: String
            var title: String
            var id: String
            var kits: [Kit]
            var preMatchStats: PreMatchStat
            var classification: Classification
            var form: [Form]

            private enum CodingKeys: String, CodingKey {
                case titleShort
                case title
                case id = "_id"
                case kits
                case preMatchStats
                case classification
                case form
            }
        }

        struct PreviousMeeting: Codable {
            struct Competition: Codable {
                var titleShort: String
            }

            struct Participant: Codable,  Identifiable{
                var titleShort: String
                var id: String

                private enum CodingKeys: String, CodingKey {
                    case titleShort
                    case id = "_id"
                }
            }

            var titleShort: String
            var winner: Int
            var date: String
            var scoreline: [String]
            var competition: Competition
            var participants: [Participant]
        }

        var id: String
        var title: String
        var date: String
        var venue: String
        var classification: Classification
        var competition: Competition
        var referee: Referee
        var participants: [Participant]
        var previousMeetings: [PreviousMeeting]

        private enum CodingKeys: String, CodingKey {
            case id = "_id"
            case title
            case date
            case venue
            case classification
            case competition
            case referee
            case participants
            case previousMeetings
        }
    }
}

So now can do this

struct ContentView: View {
    let competitions = Bundle.main.decode([Competition].self, from: "Competition.json")

    var body: some View {
        List(competitions) { competition in
            Text(competition.title)
            Text(competition.classification.title)

            ForEach(competition.fixtures) { fixture in
                Text(fixture.title)
            }
        }
    }
}

2      

@benfrain  

@NigelGee thanks very much for looking at that. I was absolutely clueless at this point!

Looks like one of the main things I got wrong is not following the nesting structure of the JSON in the structs. I somehow got it in my head that the nested structs could be defined flatter.

2      

@NigelGee  HWS+

If you use some thing like Ducky you can choose your model (sometime might have to amend but it get you most of the way). Stewart Lynch does a YouTube Video Ducky Model Editor for Swift Developers

2      

@benfrain  

Sorry for the basic questions @NigelGee; Using your second model, and the second version of body, I get an error .../ContentView.swift:18:17 Referencing initializer 'init(_:content:)' on 'ForEach' requires that 'Competition.Fixture' conform to 'Identifiable' what is Swift looking for here?

2      

@NigelGee  HWS+

Add Identifiable to struct Fixture: Codable {

struct Fixture: Codable, Identifiable {

3      

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