json - Swift:可编码复杂的 JSON

Question

当我点击 wiki API 时，我收到 JSON 响应，如下所示。我发现解码它很复杂。

{
    "continue": {
        "picontinue": 452160,
        "continue": "||pageterms"
    },
    "query": {
        "pages": [
            {
                "pageid": 164053,
                "ns": 0,
                "title": "Abdullah II of Jordan",
                "index": 2,
                "terms": {
                    "description": [
                        "King of the Hashemite Kingdom of Jordan"
                    ]
                }
            },
            {
                "pageid": 348097,
                "ns": 0,
                "title": "Abdullah Ahmad Badawi",
                "index": 9,
                "terms": {
                    "description": [
                        "Malaysian politician"
                    ]
                }
            },
            {
                "pageid": 385658,
                "ns": 0,
                "title": "Abdelaziz Bouteflika",
                "index": 8,
                "thumbnail": {
                    "source": "https://upload.wikimedia.org/wikipedia/commons/thumb/5/5b/Abdelaziz_Bouteflika_casts_his_ballot_in_May_10th%27s_2012_legislative_election_%28cropped%29.jpg/37px-Abdelaziz_Bouteflika_casts_his_ballot_in_May_10th%27s_2012_legislative_election_%28cropped%29.jpg",
                    "width": 37,
                    "height": 50
                },
                "terms": {
                    "description": [
                        "President of Algeria"
                    ]
                }
            },
            {
                "pageid": 452160,
                "ns": 0,
                "title": "Abdul Qadeer Khan",
                "index": 7,
                "terms": {
                    "description": [
                        "Pakistani nuclear scientist"
                    ]
                }
            },
            {
                "pageid": 2028438,
                "ns": 0,
                "title": "Abdelbaset al-Megrahi",
                "index": 6,
                "terms": {
                    "description": [
                        "Libyan mass murderer"
                    ]
                }
            },
            {
                "pageid": 4709709,
                "ns": 0,
                "title": "Abdul",
                "index": 1,
                "terms": {
                    "description": [
                        "family name"
                    ]
                }
            },
            {
                "pageid": 18950786,
                "ns": 0,
                "title": "Abdul Hamid II",
                "index": 5,
                "thumbnail": {
                    "source": "https://upload.wikimedia.org/wikipedia/commons/thumb/0/07/Abdul_Hamid_2.jpg/35px-Abdul_Hamid_2.jpg",
                    "width": 35,
                    "height": 50
                },
                "terms": {
                    "description": [
                        "34th sultan of the Ottoman Empire"
                    ]
                }
            },
            {
                "pageid": 19186951,
                "ns": 0,
                "title": "Abdullah of Saudi Arabia",
                "index": 4,
                "terms": {
                    "description": [
                        "former King of Saudi Arabia"
                    ]
                }
            },
            {
                "pageid": 25955055,
                "ns": 0,
                "title": "Abdullah of Pahang",
                "index": 10,
                "terms": {
                    "description": [
                        "Sultan of Pahang"
                    ]
                }
            },
            {
                "pageid": 36703624,
                "ns": 0,
                "title": "Abdel Fattah el-Sisi",
                "index": 3,
                "thumbnail": {
                    "source": "https://upload.wikimedia.org/wikipedia/commons/thumb/3/3e/Abdel_Fattah_el-Sisi_in_2017.jpg/39px-Abdel_Fattah_el-Sisi_in_2017.jpg",
                    "width": 39,
                    "height": 50
                },
                "terms": {
                    "description": [
                        "Current President of Egypt"
                    ]
                }
            }
        ]
    }
}

我只对来自上述 JSON 的 WikiPage 数据数组感兴趣，其中结构应如下所示。

struct Wikipage: Decodable {
    var pageid: Int?
    var thumbnail: String?
    var title: String?
    var description: String?
    enum CodingKeys: String, CodingKey {
        case query
        case pages
        case terms
        case description
    }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        let query = try container.nestedContainer(keyedBy: CodingKeys.self, forKey: .query)
        print(query)
    }
}

由于出现数据不匹配错误，因此我无法在此处进一步深入了解查询。我可以在不使用额外的类/变量来保存不需要的数据的情况下进行解码吗？在这种情况下我们如何解码？

        let wiki = try decoder.decode([Wikipage].self, from: data!)

Answer 1

您要求的语法是不可能的。

let wiki = try decoder.decode([Wikipage].self, from: data!)

这对维基页面数组进行解码。 stdlib 中已经有一个解码器，但它不能满足您的要求。你无法更换它。您需要自己的类型来包装它。该类型除了包装结果之外不必执行任何操作，但它必须存在。以下是构建它的方法。

首先，WikiPage 应该只是 Wikipage 部分。它不应该尝试了解有关其容器的任何信息。所以它看起来像这样:

struct Wikipage {
    let pageid: Int
    let thumbnail: URL?
    let title: String
    let description: String
}

extension Wikipage: Decodable {
    private enum CodingKeys: String, CodingKey {
        case pageid
        case title
        case thumbnail
        case terms
    }

    private struct Thumbnail: Decodable { let source: String }

    private struct Terms: Decodable { let description: [String] }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)

        self.pageid = try container.decode(Int.self, forKey: .pageid)
        self.title = try container.decode(String.self, forKey: .title)

        let source = try container.decodeIfPresent(Thumbnail.self,
                                                   forKey: .thumbnail)?.source
        self.thumbnail = source.flatMap(URL.init(string:))

        self.description = try container.decode(Terms.self,
                                                forKey: .terms).description.first ?? ""
    }
}

我删除了不需要可选的内容的可选性，并将 URL 之类的内容提升为正确的类型。请注意私有(private)帮助器结构(缩略图和术语)。这些负责嵌套。

同样的方法也适用于顶层。无需解码任何您不想要的内容，但您确实需要一种类型来保存它。

struct WikipageResult: Decodable {
    let pages: [Wikipage]

    private enum CodingKeys: String, CodingKey {
        case query
    }
    private struct Query: Decodable {
        let pages: [Wikipage]
    }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.pages = try container.decode(Query.self, forKey: .query).pages
    }
}

最后使用它:

let pages = try JSONDecoder().decode(WikipageResult.self, from: json).pages