[英]Parsing JSON using Decodable and CodingKeys in Swift 4
我正在尝试解析从URL检索到的大JSON字符串。 我正在测试的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)!
我有几个数据结构将数据放入:
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,我将打印出如下信息:
do {
let response = try JSONDecoder().decode(BookCollection.self, from: json)
for book in response.books {
print(book.genres)
}
} catch {
print(error)
}
它可以成功打印出除类型之外的所有信息。 这给了我一系列流派 ,但是我无法通过book.genres.name
来访问名称。 我必须使用: book.genres[0]
,它只给我第一个索引的结果。
有没有一种方法可以完善BookCollection
扩展中的JSON解码,然后利用book.genres.name
?
谢谢
如果您确实需要该多余的name
属性,则可以在新的扩展名中进行:
extension Array where Element == Genre {
var name: [String] {
return self.map { $0.name }
}
}
这会将上述name
属性添加到其中的每个 [Genre]
值中,包括您的Book
类型定义的值。 只要确保这确实是您要的(如果将此扩展名声明为private
,那么它将在相应的swift文件中提供)。
为了消除使用许多枚举encodingKeys并手动解码类型的需求,您可以更改数据结构以映射JSON结构格式。 请注意,下面的代码不需要嵌套结构,也可以将其并行放置。 此代码已与您编码的JSON数据一起经过测试
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)")
}
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