如何解析一个JSON数据块而不是整个JSON序列 [英] How to parse one block of JSON data instead of the entire JSON sequence

问题描述

以下是用于解析JSON API的代码.该代码有效，我能够将所有JSON值解析到下面的结构中，但是我想知道如何仅解析第一个block(?)/数组并将它们存储在该结构中，以便我可以对它们执行操作.

Below is the code that am using to parse a JSON api. The code works and i am able to parse all the JSON values into the struct below but i would like to know how to parse only the first block(?)/ array and store them in the struct so that i can perform operations on them.

     let jsonUrlString = "https://www.alphavantage.co/query?function=FX_INTRADAY&from_symbol=EUR&to_symbol=USD&interval=5min&apikey=demo"

        let urlObj = URL(string: jsonUrlString)

        URLSession.shared.dataTask(with: urlObj!) {(data, response, error) in
            guard let data = data else { return }
            do {
                let forex = try JSONDecoder().decode(Root.self, from: data)
                print(forex.timeSeriesFX5Min)
            } catch {

                print(error)
            }

            }.resume()
    }
}

struct Root: Codable {
    let timeSeriesFX5Min: [String:Forex]

    enum CodingKeys: String, CodingKey {
        case timeSeriesFX5Min = "Time Series FX (5min)"
    }
}


    // MARK: - TimeSeriesFX5Min
    struct Forex: Codable {
        let the1Open, the2High, the3Low, the4Close: String

        enum CodingKeys: String, CodingKey {
            case the1Open = "1. open"
            case the2High = "2. high"
            case the3Low = "3. low"
            case the4Close = "4. close"
        }

    }

推荐答案

我看到了两种方法，第一种方法是更改​​Root结构，在此我们需要使用消息的元数据部分

I see two ways to do this, the first requires a change to the Root struct where we need to use the Meta Data part of the message

struct Root: Codable {
    let metaData: [String: String]
    let timeSeriesFX5Min: [String:Forex]

    enum CodingKeys: String, CodingKey {
        case timeSeriesFX5Min = "Time Series FX (5min)"
        case metaData = "Meta Data"
    }
}

然后，我们选择标记为最新报价"的项目，并使用该值在时间序列字典中查找最新的价格条目

Then we pick up the item labeled "Last Refresed" and use the value to look up the latest price entry in the time series dictionary

do {
    let forex = try JSONDecoder().decode(Root.self, from: data)
    print(forex.metaData)
    if let latestTime = forex.metaData["4. Last Refreshed"], let latestForex = forex.timeSeriesFX5Min[latestTime] {
        print(latestForex)
    }        
} catch {
    print(error)
}

另一种选择是利用以下事实:时间戳记以可以正确排序的格式给出，因此我们不使用元数据而是对键进行排序并选择最后一项

Another option is to take advantage of the fact that the timestamps are given in such a format that they can be properly sorted so instead of using meta data we sort the keys and pick the last item

if let latestTime = forex.timeSeriesFX5Min.keys.sorted().last, let latestForex = forex.timeSeriesFX5Min[latestTime] {
     print(latestForex)
}

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