Problem with parsing data in nested JSON objects within Swift for iOS

Question

I am new to Swift programming and currently working on an app which will load Stock data which is in .json format. I am successfully able to load the "testStockData.json" into my code. Here is my parseJSON function within my ViewController:

func parseJSON(jsonData: Data?)
{
    // Note: jsonData has the contents of "testStockData.json"
    let decoder = JSONDecoder()
    
    do
    {
        let stockData = try decoder.decode(Stock.self, from: jsonData!)
        let tickerSymbol = stockData.metaData["Symbol"]!
        let companyName = stockData.metaData["Company"]!
        print("\(companyName) has ticker symbol: \(tickerSymbol)")
    } catch
    {
        print("Error in JSON parsing")
    }
}

I also have the following Codable Stock struct:

struct Stock : Codable {

    var metaData = [String:String]()
    
    private enum CodingKeys : String, CodingKey {
        case metaData = "Meta Data"
    }
    
}

When I run the above parseJSON function, I am successfully able to get the following printed in my output:

Apple Inc. has ticker symbol: AAPL

However I am not able to figure out how to load the nested JSON object for the "Time Series (Daily)" data? How can i parse the JSON successfully? My goal is to be able to print each day "close" price to the output, so something like:

Apple Inc. has ticker symbol: AAPL 
On 2021-04-23, closing price of AAPL was $134.32
On 2021-04-22, closing price of AAPL was $131.94
On 2021-04-21, closing price of AAPL was $133.5
On 2021-04-20, closing price of AAPL was $133.11
On 2021-04-19, closing price of AAPL was $134.84

Here is my testStockData.json file:

{
    "Meta Data": {
        "Symbol": "AAPL",
        "Company": "Apple Inc."
    },
    "Time Series (Daily)": {
            "2021-04-23": {
                "open" : "132.16",
                "high" : "135.12",
                "low"  : "132.16",
                "close": "134.32"
            },
            "2021-04-22": {
                "open" : "133.04",
                "high" : "134.15",
                "low"  : "131.41",
                "close": "131.94"
            },
            "2021-04-21": {
                "open" : "132.36",
                "high" : "133.75",
                "low"  : "131.3001",
                "close": "133.5"
            },
            "2021-04-20": {
                "open" : "135.02",
                "high" : "135.53",
                "low"  : "131.81",
                "close": "133.11"
            },
            "2021-04-19": {
                "open" : "133.51",
                "high" : "135.47",
                "low"  : "133.34",
                "close": "134.84"
            }
        }
}

Any guidance would be greatly appreciated!

jnpdx · Accepted Answer · 2021-04-24 02:59:56Z

I like to use QuickType.io (https://app.quicktype.io) for this type of problem. You can input your JSON and it gives you a Swift structure:

// MARK: - Welcome
struct Root: Codable {
    let metaData: MetaData
    let timeSeriesDaily: [String: TimeSeriesDaily]

    enum CodingKeys: String, CodingKey {
        case metaData = "Meta Data"
        case timeSeriesDaily = "Time Series (Daily)"
    }
}

// MARK: - MetaData
struct MetaData: Codable {
    let symbol, company: String

    enum CodingKeys: String, CodingKey {
        case symbol = "Symbol"
        case company = "Company"
    }
}

// MARK: - TimeSeriesDaily
struct TimeSeriesDaily: Codable {
    let timeSeriesDailyOpen, high, low, close: String

    enum CodingKeys: String, CodingKey {
        case timeSeriesDailyOpen = "open"
        case high, low, close
    }
}

Then, parsing is pretty straightforward:

do {
    let root = try JSONDecoder().decode(Root.self, from: jsonData)
    print("\(root.metaData.company) has a ticker symbol: \(root.metaData.symbol)")
    root.timeSeriesDaily.forEach { (key, value) in
        print("On \(key), closing price of \(root.metaData.symbol) was $\(value.close)")
    }
} catch {
    print("error")
}

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