Swift Codable:Nested Dictionary not being read - swift

Question

I am getting some json like so (this is pseudo, not all keys are here):
{
"absolute_magnitude_h" = "23.4";
...
"close_approach_data" = (
{
"close_approach_date" = "1994-09-03";
"epoch_date_close_approach" = 778575600000;
"orbiting_body" = Earth;
}
I have an object with this struct:
struct NEOObj:Codable {
var absoluteMagnitudeH:Float
var designation:String
var isPotentiallyHazardousAsteroid:Bool
var isSentryObject:Bool
var name:String
var nasaJPLURL:String
var neoReferenceID:String
var closeApproachData:[NEOCloseApproachData] = [NEOCloseApproachData]()
private enum CodingKeys: String, CodingKey {
case absoluteMagnitudeH = "absolute_magnitude_h"
case designation = "designation"
case isPotentiallyHazardousAsteroid = "is_potentially_hazardous_asteroid"
case isSentryObject = "is_sentry_object"
case name = "name"
case nasaJPLURL = "nasa_jpl_url"
case neoReferenceID = "neo_reference_id"
}
enum CloseApproachCodingKeys: String, CodingKey {
case closeApproachDate = "close_approach_date"
case epochDateCloseApproach = "epoch_date_close_approach"
case orbitingBody = "orbiting_body"
}
struct NEOCloseApproachData:Codable {
var closeApproachDate:Date
var epochDateCloseApproach:Date
var orbitingBody:String
enum CodingKeys: String, CodingKey {
case closeApproachDate = "close_approach_date"
case epochDateCloseApproach = "epoch_date_close_approach"
case orbitingBody = "orbiting_body"
}
}
and in my file I have this code:
if let arrNEOs = dictJSON["near_earth_objects"] as? Array<Any> {
for thisNEODict in arrNEOs {
do {
let jsonData = try JSONSerialization.data(withJSONObject: thisNEODict, options: .prettyPrinted)
let thisNEOObj = try? JSONDecoder().decode(NEOObj.self, from: jsonData)
print(thisNEOObj!.closeApproachData)
} catch {
}
}
}
But closeApproachData never gets populated. What am I doing wrong?

Answer 1

There are multiple things that would need to be changed for it to work.
closeApproachData should probably be of type [NEOCloseApproachData]. You haven't included CloseApproachCodingKeys in your code but it probably isn't right.
NEOObj.CodingKeys needs to have a case for closeApproachData which would look like
case closeApproachData = "close_approach_data"
NEOCloseApproachData needs a custom decoder to work with the dates for closeApproachDate and epochDateCloseApproach. Since the JSON has different formats for each (String and Int respectively), you can't use on the JSONDecoder.dateDecodingStrategy since it will apply to all dates.

Answer 2

The reason why after decoding you get closeApproachData property empty is the lack of the regarding key for that property into your CodingKeys enum.
Regarding to the Apple doc, it tells next:
Omit properties from the CodingKeys enumeration if they won't be
present when decoding instances, or if certain properties shouldn't be
included in an encoded representation.
That means that generated implementation of decode method for your NEOObj class omit decoding implementation for the closeApproachData property.
Here's a link at the Apple documentation about Encoding and Decoding Custom Types. You can find more details at the "Choose Properties to Encode and Decode Using Coding Keys" paragraph.
Also your custom class NEOCloseApproachData should be conformed to the Coding protocol.