Decoding Error - keyNotFound when parsing JSON data - json

Question

I am using NASA API in my iOS application for getting some images. My response from the server looks like:
{
"date": "2014-02-04T03:30:01",
"id": "LC8_L1T_TOA/LC81270592014035LGN00",
"resource": {
"dataset": "LC8_L1T_TOA",
"planet": "earth"
},
"service_version": "v1",
"url": "https://earthengine.googleapis.com/api/thumb?thumbid=bc77b079c8ecd07cd668c576c22b83a4&token=a16639b0d38dd68c586c24a6ee5299d9"
}
My request url is:
https://api.nasa.gov/planetary/earth/imagery/?lon=100.75&lat=1.5&date=2014-02-01&api_key=DEMO_KEY
My struct for decoding this response is:
import Foundation
// MARK: - EarthImages
struct EarthImages: Codable {
let date: String
let id: String
let resource: Resource
let serviceVersion: String
let url: String
private enum CodingKeys: String, CodingKey {
case date = "date"
case id = "id"
case resource = "resource"
case serviceVersion = "service_version"
case url = "url"
}
}
The problem is - when I am trying to decode my response using the following code
URLSession.shared.dataTask(with: url) { data, response, error in
if let data = data {
do {
let earthImages = try JSONDecoder().decode(EarthImages.self, from: data)
print(earthImages.url)
}
catch let error{
print(error)
}}
}.resume()
I get in console.
keyNotFound(CodingKeys(stringValue: "date", intValue: nil), Swift.DecodingError.Context(codingPath: [], debugDescription: "No value associated with key CodingKeys(stringValue: \"date\", intValue: nil) (\"date\").", underlyingError: nil))
I used PAW to check if I get correct response, and it works, so the problem more likely is in my code. How can I resolve this issue?

Answer 1

It... looks fine? (Assuming Resource is also Decodable, but that would be a separate issue). Perhaps the error is actually telling you the truth, you may be attempting to decode a JSON blob that does not have a date value.
You can explicitly see what we're attempting to decode with an added print just before we attempt to decode:
if let data = data {
print(String(data: data, encoding: .utf8)!)
do {
...
Then separately, if the date field is not guaranteed to exist in every response, you should make it optional:
struct EarthImages: Codable {
let date: String?
let id: String
let resource: Resource
let serviceVersion: String
let url: String
}
Small note, string enums dont need to be redeclared if its exactly the same as the enum case:
enum CodingKeys: String, CodingKey {
case date // "date" is implied
case id
case resource
case serviceVersion = "service_version"
case url
}
Another fun fact: JSONDecoder can also convert from snake case automatically without having to define CodingKeys if every key is consistent.
So you can also do:
struct EarthImages: Codable {
let date: String
let id: String
let resource: Resource
let serviceVersion: String
let url: String
}
...
do {
let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .convertFromSnakeCase
let earthImages = try decoder.decode(EarthImages.self, from: data)
}