json - 解码 JSON 时出错 - keyNotFound(CodingKeys

Question

当我尝试解码这个 json 时:

"polls": [
{
  "title": "title",
  "date": "date",
  "summary": "summary",
  "stats": {
    "total": {
      "dagegen gestimmt": 139,
      "nicht beteiligt": 114,
      "dafür gestimmt": 454,
      "enthalten": 2
    },
  }
}, /*<and about 76 of this>*/ ]

使用此可编码:

struct poll: Codable {
  var stats: stats
  var title: String?
  var date: String?
  var summary: String?

  struct stats: Codable {
      var total: total
      struct total: Codable {
          var nays: Int
          var yays: Int
          var nas: Int
          var abstentions: Int

          private enum CodingKeys: String, CodingKey {
             case yays = "dafür gestimmt"
             case nays = "dagegen gestimmt"
             case nas = "nicht beteiligt"
             case abstentions = "enthalten"
          }
      }
  }
}

我收到以下错误keyNotFound(CodingKeys(stringValue: "dagegen gestimmt", intValue: nil)(如果您需要完整的错误文本请告诉我)

我尝试了类似问题的一些答案，但没有任何效果。

Answer 1

显然，您出现了 total ，而 dagegen gestimmt 不存在。因此，将其设为可选，例如整数？:

struct Poll: Codable {
    let stats: Stats
    let title: String?
    let date: Date?
    let summary: String?

    struct Stats: Codable {
        let total: Total

        struct Total: Codable {
            let nays: Int?
            let yays: Int?
            let nas: Int?
            let abstentions: Int?

            private enum CodingKeys: String, CodingKey {
                case yays = "dafür gestimmt"
                case nays = "dagegen gestimmt"
                case nas = "nicht beteiligt"
                case abstentions = "enthalten"
            }
        }
    }
}

我还建议以下内容，也反射(reflect)在上面:

• 以大写字母开头类型名称(例如您的struct名称)；
• 使用 let 而不是 var，因为我们应该始终支持不变性，除非您确实要更改此 struct 中的这些值；和
• 如果您的日期格式一致，我建议将 date 设为 Date 类型，然后您可以提供 JSONDecoder 匹配的 dateDecodingStrategy(参见下面的示例)。

<小时/>

例如:

let data = """
    {
        "polls": [
            {
                "title": "New Years Poll",
                "date": "2019-01-01",
                "summary": "summary",
                "stats": {
                    "total": {
                        "dagegen gestimmt": 139,
                        "nicht beteiligt": 114,
                        "dafür gestimmt": 454,
                        "enthalten": 2
                    }
                }
            },{
                "title": "Caesar's Last Poll",
                "date": "2019-03-15",
                "summary": "summary2",
                "stats": {
                    "total": {
                        "dafür gestimmt": 42
                    }
                }
            }
        ]
    }
    """.data(using: .utf8)!

struct Response: Codable {
    let polls: [Poll]
}

do {
    let decoderDateFormatter = DateFormatter()
    decoderDateFormatter.dateFormat = "yyyy-MM-dd"
    decoderDateFormatter.locale = Locale(identifier: "en_US_POSIX")

    let userInterfaceDateFormatter = DateFormatter()
    userInterfaceDateFormatter.dateStyle = .long

    let decoder = JSONDecoder()
    decoder.dateDecodingStrategy = .formatted(decoderDateFormatter)
    let response = try decoder.decode(Response.self, from: data)
    let polls = response.polls
    for poll in polls {
        print(poll.title ?? "No title")
        print("  date:", poll.date.map { userInterfaceDateFormatter.string(from: $0) } ?? "No date supplied")
        print("  yays:", poll.stats.total.yays ?? 0)
        print("  nays:", poll.stats.total.nays ?? 0)
    }
} catch {
    print(error)
}

这会产生:

New Years Poll  date: January 1, 2019  yays: 454  nays: 139Caesar's Last Poll  date: March 15, 2019  yays: 42  nays: 0