Im very new with CoreData fetching/display and so far able to save into CoreData from a JSON fetch.
The fetched data is an array of Airport info with only three items; airport_code, access_point and image_url.
I need to add two more values to each fetched item - a lat and lon coordinate which is stored in another CoreData entity with a matching airport_code item/attribute.
Can anyone provide some guidance as to how to create a separate function to query this other CoreData during the loop sequence by using the predicate value of the airport_code? I have attached the code I have so far:
func saveData(context: NSManagedObjectContext){
xArray.forEach { (data) in
let entity = Airports(context: context)
entity.airport_code = data.airport_code
entity.access_points = data.access_points
entity.image_url = data.image_url
entity.lat = getLat()
entity.lon = getLon()
}
do{
try context.save()
print("Success Saving to CoreData: \(xArray.count)")
}
catch{
print("Error Saving to CoreData \(error.localizedDescription)")
}
}
func getLat() -> String {
@FetchRequest(entity: AllAirports.entity(), sortDescriptors: [NSSortDescriptor(keyPath: \AllAirports.airport_code, ascending: true)])
var results: FetchedResults<AllAirports>
//this is where Im lost as to how to query this CoreData to fetch the LON value when there is a match to the data.airport_code in the loop above.
return latResults
}
func getLon() -> String {
@FetchRequest(entity: AllAirports.entity(), sortDescriptors: [NSSortDescriptor(keyPath: \AllAirports.airport_code, ascending: true)])
var results: FetchedResults<AllAirports>
//this is where Im lost as to how to query this CoreData to fetch the LON value when there is a match to the data.airport_code in the loop above.
return lonResults
}
func fetchData(context: NSManagedObjectContext) {
// this function performs a JSON parse and returns the xArray above
….
First you want to take a look at the response here What is the best way to do a fetch request in CoreData? to get an idea how a programmatic fetch request may look like.
As I understand your problem now, you want to write two methods getLat() and getLon() which are going to fetch the coordinates for an airport.
I would recommend to write a single function as shown below which looks up your airport in AllAirports using the given code and returns the tuple with the coordinates found.
func getCoord(airport_code: String) -> (lon: Double, lat: Double)? {
let request: NSFetchRequest<AllAirports> = AllAirports.fetchRequest()
request.predicate = NSPredicate(format: "airport_code == %@", airport_code)
if let result = try? viewContext.fetch(request) {
print("Found \(result.count) airports matching \(airport_code)")
// Just return the first matched airport
if let first = result.first {
return (first.longitude, first.latitude)
}
}
return nil
}
A better solution would be to add an extension to you AllAirports which returns an entry for a given (hopefully unique!) airport_code:
extension AllAirports {
static func airport(byCode airportCode: String, in context: NSManagedObjectContext) -> AllAirports? {
let request: NSFetchRequest<AllAirports> = fetchRequest()
request.predicate = NSPredicate(format: "airport_code == %@", airportCode)
if let result = try? context.fetch(request) {
return result.first
}
return nil
}
}
This could then be used in your code as follows:
func saveData(context: NSManagedObjectContext){
xArray.forEach { (data) in
let entity = Airports(context: context)
entity.airport_code = data.airport_code
entity.access_points = data.access_points
entity.image_url = data.image_url
if let airport = AllAirports.airport(byCode: data.airport_code, in: context) {
entity.lat = airport.latitude
entity.lon = airport.longitude
}
}