Get data from Firestore and properly append to array - swift

Question

I'm trying to fetch data from Firestore. I've already got the following code but how do I properly append to shelters?
Current error:
Value of type '[String : Any]' has no member 'title'
class FirebaseSession: ObservableObject {
#Published var shelters: [Shelter] = []
let ref = Firestore.firestore().collection("shelters")
getShelters() {
ref.getDocuments() { (querySnapshot, err) in
if let err = err {
print("Error getting documents: \(err)")
} else {
for document in querySnapshot!.documents {
let value = document.data()
let shelter = Shelter(id: Int(value.id), title: value.title, image: value.image, availableSpaces: value.available, distance: value.distance, gender: value.gender)
self.$shelters.append(shelter)
}
}
}
}
}
class Shelter {
var id: Int
var title: String
var image: String
var availableSpaces: Int
var distance: Double
var gender: String?
init?(id: Int, title: String, image: String, availableSpaces: Int, distance: Double, gender: String?) {
if id < 0 || title.isEmpty || image.isEmpty || availableSpaces < 0 || distance < 0 {
return nil
}
self.id = id
self.title = title
self.image = image
self.availableSpaces = availableSpaces
self.distance = distance
self.gender = gender
}
}
EDIT:
let shelter = Shelter(id: value["id"] as? Int ?? -1, title: value["title"] as? String ?? "", image: value["image"] as? String ?? "", available: value["available"] as? Int ?? -1, distance: value["distance"] as? Double ?? -1, gender: value["gender"] as? String ?? "")

Answer 1

let shelter = Shelter(id: Int(value.id), title: value.title, image: value.image, availableSpaces: value.available, distance: value.distance, gender: value.gender)
Here value is of type [String:Any]. So you cant do value.title . You need to do value["title"] as? String ?? "" and Similarly for id,image,distance,etc.
So the final code becomes:
let shelter = Shelter(id: Int(value["id"], title: value["title"], image: value["image"], availableSpaces: value["available"], distance: value["distance"], gender: value["gender"])
Downcast it accordingly.
UPDATE
replace your code with this
if let shelter = Shelter(id: value["id"] as? Int ?? -1, title: value["title"] as? String ?? "", image: value["image"] as? String ?? "", available: value["available"] as? Int ?? -1, distance: value["distance"] as? Double ?? -1, gender: value["gender"] as? String ?? "") {
self.shelters.append(shelter)
} else {
print("provided data is wrong.")
}

Answer 2

There are a number of issues with the original code:
Instead of implementing a function to fetch the shelters, the following snippet in your code creates a computed property - not sure this is what you intended:
getShelters() {
...
}
I'd recommend replacing this with a proper function.
No need to use a class for your data model - especially as you seem to be using SwiftUI.
Instead of mapping the fetched documents manually (and having to deal with nil values, type conversion etc. yourself, I'd recommend using Firestore's Codable support.
I've written about this extensively in my article SwiftUI: Mapping Firestore Documents using Swift Codable - Application Architecture for SwiftUI & Firebase | Peter Friese.
Here's how your code might look like when applying my recommendations:
struct Shelter: Codable, Identifiable {
#DocumentID var id: String?
var title: String
var image: String
var availableSpaces: Int
var distance: Double
var gender: String?
}
class FirebaseSession: ObservableObject {
#Published var shelters = [Shelter]()
private var db = Firestore.firestore()
private var listenerRegistration: ListenerRegistration?
deinit {
unsubscribe()
}
func unsubscribe() {
if listenerRegistration != nil {
listenerRegistration?.remove()
listenerRegistration = nil
}
}
func subscribe() {
if listenerRegistration == nil {
listenerRegistration = db.collection("shelters").addSnapshotListener { (querySnapshot, error) in
guard let documents = querySnapshot?.documents else {
print("No documents")
return
}
self.shelters = documents.compactMap { queryDocumentSnapshot in
try? queryDocumentSnapshot.data(as: Shelter.self)
}
}
}
}
}
Note that:
we're able to do away with the constructor for Shelter
the shelter property will now be automatically updated whenever a shelter is added to the shelter collection in Firestore
the code won't break if a document doesn't match the expected data structure
I marked the Shelter struct as identifiable, so that you can directly use it inside a List view. #DocumentID instructs Firestore to map the document ID to the respective attribute on the struct.