How to map an array in a Firestore document to Swift? - swift

Question

How can I map the arrays in the following Firestore documents to Swift?
Here is my data model in Swift:
import Foundation
struct CityList: Codable, Hashable {
var name: String
var latitude: String
var longitude: String
}
struct Cities: Codable, Identifiable {
var id: String = UUID().uuidString
var citiesList: [CityList]
}
and here is my view model:
class WeatherList: ObservableObject {
#Published var cities = [CityList]()
func fetchCities(userInfo: UserInfo) {
self.cities.removeAll()
let db = Firestore.firestore()
.collection("cities")
.document(userInfo.user.uid)
db.getDocument() { (document, error) in
if let document = document, document.exists {
guard let itemIDs = document.get("citiesList") else {
return
}
for i in itemIDs {
print(i.value)
}
}
else {
return
}
}
}
}
When executed, it displays an error: Protocol 'Any' as a type cannot conform to 'Sequence'
How can I map this document?

Answer 1

You're almost there, just need to call data(as:) to perform the mapping.
Here is the updated code:
import Foundation
struct City: Codable, Hashable {
var name: String
var latitude: String
var longitude: String
}
struct Cities: Codable, Identifiable {
#DocumentID var id: String?
var cities: [City]
}
class WeatherViewModel: ObservableObject {
#Published var cities = [City]()
func fetchCities(userInfo: UserInfo) {
let docRef = Firestore.firestore()
.collection("cities")
.document(userInfo.user.uid)
docRef.getDocument { document, error in
if let error = error as NSError? {
self.errorMessage = "Error getting document: \(error.localizedDescription)"
}
else {
if let document = document {
do {
let citiesDocument = try document.data(as: Cities.self)
self.cities = citiesDocument.cities
}
catch {
print(error)
}
}
}
}
}
}
For a comprehensive overview of how to map Firestore data to / from Swift, check out my blog post Mapping Firestore Data in Swift - The Comprehensive Guide