Swift Firestore custom objects from query while listening for realtime updates with snapshotListener - swift

Question

I've got issues converting querySnapshots that is observed for changes with snapshotListener to custom objects.
This is my code but the compiler is complaining:
func getCartData(db: Firestore){
db.collection("test")
.whereField("Cart", arrayContains: "testItem")
.addSnapshotListener { querySnapshot, error in
guard let documents = querySnapshot?.documents else {
print("Error fetching document: \(error!)")
return
}
for doc in documents {
guard let data = doc.data() else { //here is an error saying: Initializer for conditional binding must have Optional type, not '[String : Any]'
print("Document data was empty.")
return
}
let result = Result {
try doc.data(as: CartDataDocument.self)
}
switch result {
case .success(let userDataDoc):
if let userDataDoc = userDataDoc {
// A `userDataDoc` value was successfully initialized from the DocumentSnapshot.
self.cartData = userDataDoc
} else {
// A nil value was successfully initialized from the DocumentSnapshot,
// or the DocumentSnapshot was nil.
print("Document does not exist")
}
case .failure(let error):
// A `userDataDoc` value could not be initialized from the DocumentSnapshot.
print("Error decoding UserDataDocument: \(error)")
}
}
}
}
I was able to make custom objects of one Firestore document that got listened to with a snapshotListener but had no luck with this query.

Answer 1

The error seems correct. If you look at the declaration that Xcode shows while autocompleting, doc.data() is indeed a non-nullable [String: Any].
If you want to check if a document is empty you can do it like this:
guard !doc.data().isEmpty else {
print("Document data was empty.")
return
}
Otherwise, you could also override init(from decoder: Decoder) throws in CartDataDocument and provide default values for all keys. This obviously goes in a a different direction: instead of ignoring empty documents, you are adding them to the list with default values. But I've got to ask: why do you have empty documents?