Parsing Met Office JSON - json

Question

I am wanting to parse the weather data from the Met Office for Plymouth. The structure that I have is the following:
struct WeatherRoot: Codable {
var siteRep: SiteRep
private enum CodingKeys: String, CodingKey {
case siteRep = "SiteRep"
}
}
struct SiteRep: Codable {
var dataWx: DataWx
var dataDV: DataDV
private enum CodingKeys: String, CodingKey {
case dataWx = "Wx"
case dataDV = "DV"
}
}
struct DataWx: Codable {
var param: [Param]?
private enum CodingKeys: String, CodingKey {
case param = "Param"
}
}
struct Param: Codable {
var headings: WeatherDataHeadings
private enum CodingKeys: String, CodingKey {
case headings = "Param"
}
}
struct WeatherDataHeadings: Codable {
var name: String
var unit: String
var title: String
private enum CodingKeys: String, CodingKey {
case name = "name"
case unit = "units"
case title = "$"
}
}
struct DataDV: Codable {
var dataDate: String
var type: String
var location: LocationDetails
private enum CodingKeys: String, CodingKey {
case dataDate = "dataType"
case type = "type"
case location = "Location"
}
}
struct LocationDetails: Codable {
var id: String
var latitude: String
var longitude: String
var name: String
var country: String
var continent: String
var elevation: String
var period: [Period]
private enum CodingKeys: String, CodingKey {
case id = "i"
case latitude = "lat"
case longitude = "lon"
case name
case country
case continent
case elevation
case period = "Period"
}
}
struct Period: Codable {
var type: String
var value: String
var rep: [Rep]
private enum CodingKeys: String, CodingKey {
case type = "type"
case value = "value"
case rep = "Rep"
}
}
struct Rep: Codable {
var windDirection: String
var feelsLikeTemperature: String
var windGust: String
var humidity: String
var precipitation: String
var windSpeed: String
var temperature: String
var visibility: String
var weatherType: String
var uvIndex: String
var time: String
private enum CodingKeys: String, CodingKey {
case windDirection = "D"
case feelsLikeTemperature = "F"
case windGust = "G"
case humidity = "H"
case precipitation = "Pp"
case windSpeed = "S"
case temperature = "T"
case visibility = "V"
case weatherType = "W"
case uvIndex = "U"
case time = "$"
}
}
extension WeatherRoot {
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
siteRep = try values.decode(SiteRep.self, forKey: .siteRep)
}
}
extension SiteRep {
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
dataWx = try values.decode(DataWx.self, forKey: .dataWx)
dataDV = try values.decode(DataDV.self, forKey: .dataDV)
}
}
extension DataWx {
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
param = try values.decodeIfPresent([Param].self, forKey: .param)
}
}
extension Param {
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
headings = try values.decode(WeatherDataHeadings.self, forKey: .headings)
}
}
extension WeatherDataHeadings {
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
name = try values.decode(String.self, forKey: .name)
unit = try values.decode(String.self, forKey: .unit)
title = try values.decode(String.self, forKey: .title)
}
}
extension DataDV {
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
dataDate = try values.decode(String.self, forKey: .dataDate)
type = try values.decode(String.self, forKey: .type)
location = try values.decode(LocationDetails.self, forKey: .location)
}
}
extension LocationDetails {
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
id = try values.decode(String.self, forKey: .id)
latitude = try values.decode(String.self, forKey: .latitude)
longitude = try values.decode(String.self, forKey: .longitude)
name = try values.decode(String.self, forKey: .name)
country = try values.decode(String.self, forKey: .country)
continent = try values.decode(String.self, forKey: .continent)
elevation = try values.decode(String.self, forKey: .elevation)
period = try [values.decode(Period.self, forKey: .period)]
}
}
extension Period {
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
type = try values.decode(String.self, forKey: .type)
value = try values.decode(String.self, forKey: .value)
rep = try [values.decode(Rep.self, forKey: .rep)]
}
}
extension Rep {
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
windDirection = try values.decode(String.self, forKey: .windDirection)
feelsLikeTemperature = try values.decode(String.self, forKey: .feelsLikeTemperature)
windGust = try values.decode(String.self, forKey: .windGust)
humidity = try values.decode(String.self, forKey: .humidity)
precipitation = try values.decode(String.self, forKey: .precipitation)
windSpeed = try values.decode(String.self, forKey: .windSpeed)
temperature = try values.decode(String.self, forKey: .temperature)
visibility = try values.decode(String.self, forKey: .visibility)
weatherType = try values.decode(String.self, forKey: .weatherType)
uvIndex = try values.decode(String.self, forKey: .uvIndex)
time = try values.decode(String.self, forKey: .time)
}
}
The data that I am trying to parse is:
{"SiteRep":{"Wx":{"Param":[{"name":"F","units":"C","$":"Feels Like Temperature"},{"name":"G","units":"mph","$":"Wind Gust"},{"name":"H","units":"%","$":"Screen Relative Humidity"},{"name":"T","units":"C","$":"Temperature"},{"name":"V","units":"","$":"Visibility"},{"name":"D","units":"compass","$":"Wind Direction"},{"name":"S","units":"mph","$":"Wind Speed"},{"name":"U","units":"","$":"Max UV Index"},{"name":"W","units":"","$":"Weather Type"},{"name":"Pp","units":"%","$":"Precipitation Probability"}]},"DV":{"dataDate":"2018-03-16T19:00:00Z","type":"Forecast","Location":{"i":"3844","lat":"50.7366","lon":"-3.40458","name":"EXETER AIRPORT 2","country":"ENGLAND","continent":"EUROPE","elevation":"27.0","Period":[{"type":"Day","value":"2018-03-16Z","Rep":[{"D":"SE","F":"8","G":"16","H":"78","Pp":"6","S":"11","T":"11","V":"EX","W":"7","U":"1","$":"900"},{"D":"SE","F":"6","G":"11","H":"88","Pp":"6","S":"9","T":"8","V":"MO","W":"7","U":"1","$":"1080"},{"D":"E","F":"5","G":"13","H":"92","Pp":"5","S":"4","T":"7","V":"GO","W":"7","U":"0","$":"1260"}]},{"type":"Day","value":"2018-03-17Z","Rep":[{"D":"E","F":"5","G":"16","H":"90","Pp":"86","S":"7","T":"7","V":"GO","W":"12","U":"0","$":"0"},{"D":"ENE","F":"5","G":"13","H":"93","Pp":"82","S":"7","T":"7","V":"GO","W":"15","U":"0","$":"180"},{"D":"ENE","F":"2","G":"22","H":"91","Pp":"40","S":"11","T":"6","V":"MO","W":"9","U":"0","$":"360"},{"D":"NE","F":"-2","G":"29","H":"84","Pp":"44","S":"16","T":"3","V":"VG","W":"12","U":"1","$":"540"},{"D":"ENE","F":"-4","G":"29","H":"75","Pp":"17","S":"16","T":"2","V":"VG","W":"8","U":"2","$":"720"},{"D":"ENE","F":"-4","G":"29","H":"72","Pp":"20","S":"16","T":"2","V":"VG","W":"8","U":"1","$":"900"},{"D":"NE","F":"-6","G":"25","H":"73","Pp":"17","S":"13","T":"0","V":"VG","W":"8","U":"1","$":"1080"},{"D":"NE","F":"-7","G":"22","H":"81","Pp":"16","S":"11","T":"-1","V":"VG","W":"8","U":"0","$":"1260"}]},{"type":"Day","value":"2018-03-18Z","Rep":[{"D":"NE","F":"-8","G":"22","H":"86","Pp":"51","S":"11","T":"-2","V":"VG","W":"24","U":"0","$":"0"},{"D":"NE","F":"-8","G":"22","H":"87","Pp":"60","S":"11","T":"-2","V":"GO","W":"24","U":"0","$":"180"},{"D":"NE","F":"-8","G":"25","H":"88","Pp":"66","S":"13","T":"-1","V":"MO","W":"24","U":"0","$":"360"},{"D":"ENE","F":"-8","G":"29","H":"92","Pp":"84","S":"16","T":"-1","V":"PO","W":"27","U":"1","$":"540"},{"D":"ENE","F":"-5","G":"31","H":"84","Pp":"63","S":"16","T":"1","V":"MO","W":"24","U":"2","$":"720"},{"D":"ENE","F":"-5","G":"29","H":"83","Pp":"26","S":"16","T":"1","V":"MO","W":"8","U":"1","$":"900"},{"D":"ENE","F":"-6","G":"25","H":"80","Pp":"24","S":"13","T":"0","V":"GO","W":"8","U":"1","$":"1080"},{"D":"ENE","F":"-7","G":"25","H":"78","Pp":"18","S":"13","T":"-1","V":"GO","W":"8","U":"0","$":"1260"}]},{"type":"Day","value":"2018-03-19Z","Rep":[{"D":"NE","F":"-8","G":"25","H":"78","Pp":"12","S":"11","T":"-2","V":"VG","W":"7","U":"0","$":"0"},{"D":"NE","F":"-8","G":"25","H":"78","Pp":"10","S":"13","T":"-2","V":"VG","W":"7","U":"0","$":"180"},{"D":"NE","F":"-8","G":"22","H":"77","Pp":"11","S":"11","T":"-2","V":"VG","W":"7","U":"0","$":"360"},{"D":"NE","F":"-7","G":"27","H":"69","Pp":"3","S":"13","T":"0","V":"VG","W":"3","U":"1","$":"540"},{"D":"ENE","F":"-3","G":"29","H":"57","Pp":"2","S":"16","T":"3","V":"VG","W":"3","U":"3","$":"720"},{"D":"NE","F":"0","G":"29","H":"49","Pp":"1","S":"16","T":"5","V":"VG","W":"1","U":"1","$":"900"},{"D":"NE","F":"-1","G":"20","H":"59","Pp":"1","S":"11","T":"4","V":"VG","W":"1","U":"1","$":"1080"},{"D":"NNE","F":"-4","G":"22","H":"73","Pp":"1","S":"11","T":"2","V":"VG","W":"0","U":"0","$":"1260"}]},{"type":"Day","value":"2018-03-20Z","Rep":[{"D":"NNE","F":"-4","G":"18","H":"81","Pp":"5","S":"9","T":"1","V":"VG","W":"7","U":"0","$":"0"},{"D":"N","F":"-3","G":"18","H":"86","Pp":"5","S":"9","T":"2","V":"GO","W":"7","U":"0","$":"180"},{"D":"N","F":"-3","G":"18","H":"88","Pp":"5","S":"9","T":"2","V":"GO","W":"7","U":"0","$":"360"},{"D":"N","F":"0","G":"20","H":"78","Pp":"5","S":"9","T":"4","V":"VG","W":"7","U":"1","$":"540"},{"D":"NNE","F":"3","G":"22","H":"68","Pp":"1","S":"11","T":"7","V":"VG","W":"3","U":"3","$":"720"},{"D":"N","F":"5","G":"22","H":"62","Pp":"5","S":"11","T":"8","V":"VG","W":"7","U":"1","$":"900"},{"D":"NNW","F":"3","G":"13","H":"72","Pp":"5","S":"7","T":"6","V":"VG","W":"7","U":"1","$":"1080"},{"D":"NNW","F":"1","G":"11","H":"82","Pp":"5","S":"4","T":"4","V":"GO","W":"7","U":"0","$":"1260"}]}]}}}}
However when I decode the JSON to the structure I get the error:
Error Serializing Json: keyNotFound(Clothing_Prediction_iOS_Application.Param.(CodingKeys in _99F6E563F35EF627A75B06F8891FEB0F).headings, Swift.DecodingError.Context(codingPath: [Clothing_Prediction_iOS_Application.WeatherRoot.(CodingKeys in _99F6E563F35EF627A75B06F8891FEB0F).siteRep, Clothing_Prediction_iOS_Application.SiteRep.(CodingKeys in _99F6E563F35EF627A75B06F8891FEB0F).dataWx, Clothing_Prediction_iOS_Application.DataWx.(CodingKeys in _99F6E563F35EF627A75B06F8891FEB0F).param, Foundation.(_JSONKey in _12768CA107A31EF2DCE034FD75B541C9)(stringValue: "Index 0", intValue: Optional(0))], debugDescription: "No value associated with key headings (\"Param\").", underlyingError: nil))
I have tried looking at optionals however I can not see why I am getting this error.

Answer 1

It looks like you're duplicating Param in your data structures. DataWx has case param = "Param", which is OK. But then Param has case headings = "Param", which is not in your JSON. So your JSON starts off with
{"SiteRep":{"Wx":{"Param":[{"name"...
But your data structures expect something like
{"SiteRep":{"Wx":{"Param":{"Param":...
The error isn't very clear but this seems to be what it's trying to tell you.

Answer 2

If you parse through the error message (messy, I know), you will find that it's telling you 2 things:
Key not found: headings
At key path: siteRep/dataWx/param[0]
The key path is the name of the properties in your data model. If you convert them back to how you mapped it in your various CodingKeyss, you will get the JSON path: SiteRep/Wx/Param[0]. There's no headings to found there.
How to fix it:
Remove your current Param struct
Rename WeatherDataHeadings to Param
You also have another mapping error in DataDV:
struct DataDV: Codable {
// Better parse date as Date, and not as String. This
// requires set the dateDecodingStrategy. See below.
var dataDate: Date
var type: String
var location: LocationDetails
private enum CodingKeys: String, CodingKey {
case dataDate = "dataDate" // not "dataType"
case type = "type"
case location = "Location"
}
}
And you wrote way more code than needed. You can delete all these extension. The compiler can synthesize them for you.
Here's how you decode it:
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .iso8601
let weatherRoot = try decoder.decode(WeatherRoot.self, from: jsonData)