使用顶级数据在 Swift 中解码对结构数组的 JSON 响应

Question

我有一个来自 API 的 JSON 响应，如下所示：

{ 
"data": {
    "author_id": "wxyz",
    "author_name": "Will",
    "language": "English",
    "books": [
        {"book_id":"abc1", "book_name":"BookA"},
        {"book_id":"def2", "book_name":"BookB"},
        {"book_id":"ghi3", "book_name":"BookC"}
    ]
  }
}

目前我的Book 结构如下所示：

struct Book: Codable {
    let book_id: String
    let book_name: String
}

但我想要一个像这样的Book（带有来自顶层的数据）：

struct Book: Codable {
    let book_id: String
    let book_name: String
    let author: Author
    let language: String
}

使用 Codable（/解码自定义类型），如何将上面的 JSON 响应直接转换为书籍列表（而某些数据来自顶级对象）？

当我使用 decode 时，我可以自动将 books 数组解码为 Book 数组：

let books = try decoder.decode([Book].self, from: jsonData)

但我找不到传递作者姓名和 ID 或语言的方法，因为它位于顶层

Answer 1

您也许可以使用自定义 init(decoder:) 来做到这一点，但另一种方法是隐藏您坚持使用 JSON 模型的内部实现，并使用 lazy var 或计算获取。 Lazy var 只会加载一次，这取决于您是否保留根目录。

struct Root: Codable {
    //Hidde,
    private let data: RootData

    //Hidden
    struct RootData: Codable {
        let author_id: String
        let author_name: String

        let language: String

        let books: [RootBook]
    }
    //Hidden
    struct RootBook: Codable {
        let book_id: String
        let book_name: String
    }

    lazy var books: [Book] = {
        let author = Author(id: data.author_id, name: data.author_name)
        return data.books.map {
            Book(id: $0.book_id, name: $0.book_name, author: author, language: data.language)
        }
    }()

    var books2: [Book] {
        let author = Author(id: data.author_id, name: data.author_name)
        return data.books.map {
            Book(id: $0.book_id, name: $0.book_name, author: author, language: data.language)
        }
    }
}

//Visible
struct Book: Codable {
    let id: String
    let name: String
    let author: Author
    let language: String
}
//Visible
struct Author: Codable {
    let id: String
    let name: String
}

用途：

do {
    var root = try JSONDecoder().decode(Root.self, from: jsonData)
    print(root)
    print("Books: \(root.books)") //Since it's a lazy var, it need to be mutable
} catch {
    print("Error: \(error)")
}

或

do {
    let root = try JSONDecoder().decode(Root.self, from: jsonData)
    print(root)
    print("Books: \(root.books2)")
} catch {
    print("Error: \(error)")
}

旁注：最简单的方法是坚持使用 JSON 模型。现在，拥有内部模型也可能很有趣，也就是说，你有自己的 Book 类，你从 Root 初始化。因为明天，JSON 可能会更改（更改服务器等）。然后用于您的视图的模型（如何显示它们）也可能不同...... 分离你的层，无论你想使用 MVC、MVVM、VIPER 等。

编辑：

您可以覆盖init(decoder:)，但它会使代码更清晰吗？我发现它比以前的版本更难编写（意思是更难调试/修改？）

struct Root2: Codable {
    let books: [Book2]

    private enum TopLevelKeys: String, CodingKey {
        case data
    }
    private enum SubLevelKeys: String, CodingKey {
        case books
        case authorId = "author_id"
        case authorName = "author_name"
        case language
    }
    private enum BoooKeys: String, CodingKey {
        case id = "book_id"
        case name = "book_name"
    }
    init(from decoder: Decoder) throws {
        let topContainer = try decoder.container(keyedBy: TopLevelKeys.self)
        let subcontainer = try topContainer.nestedContainer(keyedBy: SubLevelKeys.self, forKey: .data)
        var bookContainer = try subcontainer.nestedUnkeyedContainer(forKey: .books)
        var books: [Book2] = []
        let authorName = try subcontainer.decode(String.self, forKey: .authorName)
        let authorid = try subcontainer.decode(String.self, forKey: .authorId)
        let author = Author(id: authorid, name: authorName)
        let language = try subcontainer.decode(String.self, forKey: .language)
        while !bookContainer.isAtEnd {
            let booksubcontainer = try bookContainer.nestedContainer(keyedBy: BoooKeys.self)
            let bookName = try booksubcontainer.decode(String.self, forKey: .name)
            let bookId = try booksubcontainer.decode(String.self, forKey: .id)
            books.append(Book2(book_id: bookId, book_name: bookName, author: author, language: language))
        }
        self.books = books
    }
}
struct Book2: Codable {
    let book_id: String
    let book_name: String
    let author: Author
    let language: String
}