Swift Codable的一个拓展--XPath语法

Codable JSON转模型，简单好用又高效，XPath快速JSON子节点定位，二者合二为一，简单高效快捷又好用。
样例模型，Order与Goods都是Codable：

struct Order: Codable {
    var id: String?
    var money: String?
    var goods: [Goods]?
}

struct Goods: Codable {
    var id: String?
    var name: String?
    var price: String?
    var count: Int?
}

JSON样例:

{
    "msg": "",
    "data": {
        "orders": [{
            "id": "1234",
            "money": "65.0",
            "goods": [{
                "id": "a10",
                "price": "25,0",
                "name": "重窝小旋风",
                "count": 1
            }, {
                "id": "b11",
                "price": "20.0",
                "name": "逍遥青",
                "count": 2
            }]
        }, {
            "id": "5678",
            "money": "708.0",
            "goods": [{
                "id": "c123",
                "price": "708.0",
                "name": "一帆精工擎天柱红色纪念款钓台",
                "count": 1
            }]
        }],
        "total": 2
    },
    "code": 0
}

JSON转模型方法：

public func decode<T : Decodable>(_ json : Any) -> T? {
    guard JSONSerialization.isValidJSONObject(json) else {
        return nil
    }
    guard let data = try? JSONSerialization.data(withJSONObject: json, options: .init()) else {
        return nil
    }
    let decoder = JSONDecoder()
    guard let result = try? decoder.decode(T.self, from: data) else {
        return nil
    }
    return result
}

public func decode<T : Decodable>(_ json : [String: Any], xpath: String) -> T? {
    guard let target = json.xpath(xpath) else {
        return nil
    }
    return decode(target)
}

Codable使用：

let data = json["data"] as? [String: Any]
let orders = data?["orders"] as? [[String: Any]] ?? []
let results: [Order] = decode(orders)

XPath+Codable，一行搞定:

let results: [Order] = decode(json, xpath: "data.orders")

结合RxSwift使用样例：

func goodsList(page: Int, keywords: String? = nil, success: (([Goods]) -> ())?, failure: ErrorHandler?) {
        provider.rx.request(.goodsList(page: page, keywords: keywords))
            .mapCode()
            .mapObject([Goods].self, xpath: "data.spus")
            .subscribe { goods in
                success?(goods)
            } onError: { error in
                failure?(error)
            }
            .disposed(by: bag)
    }

RxSwift之mapObject：

public extension PrimitiveSequence where Trait == SingleTrait, Element == [String: Any] {
    func mapObject<T: Codable>(_ type: T.Type) -> Single<T> {
        return flatMap { dict in
            guard let t: T = decode(dict) else {
                throw YXNetworkError.JsonMap
            }
            return .just(t)
        }
    }
    
    func mapObject<T: Codable>(_ type: T.Type, xpath: String) -> Single<T> {
        return flatMap { dict in
            guard let result = dict.xpath(xpath) else {
                throw YXNetworkError.JsonMap
            }
            guard let t: T = decode(result) else {
                throw YXNetworkError.JsonMap
            }
            return .just(t)
        }
    }
}

最后附上XPath的实现方法：

public extension Dictionary where Key == String, Value == Any {
    func xpath(_ xpath: String) -> Any? {
        guard xpath.count > 0 else {
            return nil
        }
        let paths = xpath.components(separatedBy: ".")
        var result = self
        var correct = true
        for i in 0 ..< paths.count {
            let path = paths[i]
            if i < paths.count - 1 {
                if let next = result[path] as? [String: Any] {
                    result = next
                } else {
                    correct = false
                    break
                }
            } else {
                if let next = result[path] {
                    return next
                } else {
                    correct = false
                    break
                }
            }
        }
        guard correct else {
            return nil
        }
        return result
    }
}