在 Swift 4 中使用 Decodable 和 CodingKeys 解析 JSON

Question

我正在尝试解析从URL检索的大型JSON字符串。我用来测试的 JSON 如下：

let json = """
{
"feed": {
    "title": "Harry Potter",
    "test": "I dont want this value",
    "results": [
        {
        "author": "JK Rowling",
        "artworkURL": "A url",
        "genres": [
            {
                "name": "Fantasy"
            },
            {
                "name": "Scifi"
            }
        ],
            "name": "Goblet of Fire",
            "releaseDate": "2000-07-08"
        },
        {
        "author": "JK Rowling",
        "artworkURL": "A url",
        "genres": [
            {
                "name": "Fantasy"
            },
            {
                "name": "Scifi"
            }
            ],
            "name": "Half Blood Prince",
            "releaseDate": "2009-07-15"
            }
        ]
    }
}
""".data(using: .utf8)!

我有几个数据结构来放置数据：

struct Genre: Decodable {
    let name: String
}
struct Book: Decodable {
    let author: String
    let artworkURL: URL
    let genres: [Genre]
    let name: String
    let releaseDate: String
}
struct BookCollection {
    let title: String
    let books: [Book]
    enum CodingKeys: String, CodingKey {
        case feed
    }
    enum FeedKeys: String, CodingKey {
        case title, results
    }
    enum ResultKeys: String, CodingKey {
        case author, artworkURL, genres, name, releaseDate
    }
    enum GenreKeys: String, CodingKey {
        case name
    }
}
extension BookCollection: Decodable {
    init(from decoder: Decoder) throws {
        let values = try decoder.container(keyedBy: CodingKeys.self)
        let feed = try values.nestedContainer(keyedBy: FeedKeys.self, 
    forKey: .feed)
        self.title = try feed.decode(String.self, forKey: .title)
        self.books = try feed.decode([Track].self, forKey: .results)
    }
}

然后我打印出这样的信息：

do {
    let response = try JSONDecoder().decode(BookCollection.self, from: json)
    for book in response.books {
        print(book.genres)
    }
} catch {
    print(error)
}

它成功地打印了除流派以外的所有信息。这给了我一系列流派，但我做不到 book.genres.name以访问该名称。 我必须使用： book.genres[0]它只为我提供了第一个索引的结果。

有没有办法在我的BookCollection扩展中完善我的 JSON 解码，然后利用book.genres.name？

谢谢

Answer 1

如果你真的需要这个额外的name属性，你可以在一个新的扩展中这样做：

extension Array where Element == Genre {
    var name: [String] {
        return self.map { $0.name }
    }
}

这会将上述 name 属性添加到每个[Genre]值，包括由Book类型定义的值。只要确保这真的是你所追求的（如果将此扩展声明为 private，那么它将在相应的 swift 文件中可用）。

Answer 2

为了消除使用许多枚举编码键和手动解码类型的需要，您可以更改数据结构以映射 JSON 结构格式。注意下面的代码，没有必要嵌套结构，你也可以把它并行放。此代码使用编码的 JSON 数据进行测试

public struct HarryPotterFeed: Codable {
  public let feed: BookCollection
  public struct BookCollection: Codable {
    public let title: String
    public let books: [Book]
    // map properties books to json's "results"
    enum CodingKeys: String, CodingKey {
      case title  // needs to come along 
      case books = "results"
    }
    public struct Book: Codable {
      public let author, name, artworkURL, releaseDate : String
      public let genres: [Genre]
      public struct Genre: Codable {
        public let name: String
      }
    }
  }
}
// Decode JSON 
do {
  let response = try JSONDecoder().decode(HarryPotterFeed.self, from: json)
  for book in response.feed.books {
    for name in book.genres {
      print(name)
    }
  }
} catch {
  print("PROBLEM DECODING JSON (error)")
}