Swift / Firestore setData with multiple documents at once causes app to crash-CodePudding

I am creating a fitness app where you can favorite trainer accounts and when you favorite a trainer account I want to add all workouts posted by that trainer to the current user's feed.

When you favorite a trainer account I use this function to add the workouts to a collection on firestore:

func addToUserFeed() {
    guard let trainerUid = trainer.id else { return }
    guard let currentUid = AuthViewModel.shared.userSession?.uid else { return }

    COLLECTION_WORKOUTS.whereField("ownerUid", isEqualTo: trainerUid).addSnapshotListener { snapshot, _ in
        
        guard let workoutIDs = snapshot?.documents.map({ $0.documentID }) else { return }
        
        workoutIDs.forEach { id in
            COLLECTION_USERS.document(currentUid).collection("user-feed").document(id).setData([:])
        }

    }
}

Similarly, when you unfavorite a trainer I am removing those workouts from the user feed collection with this function:

func removeFromUserFeed() {
    guard let trainerUid = trainer.id else { return }
    guard let currentUid = AuthViewModel.shared.userSession?.uid else { return }

    COLLECTION_WORKOUTS.whereField("ownerUid", isEqualTo: trainerUid).addSnapshotListener { snapshot, _ in
        
        guard let workoutIDs = snapshot?.documents.map({ $0.documentID }) else { return }
        
        workoutIDs.forEach { id in
            COLLECTION_USERS.document(currentUid).collection("user-feed").document(id).delete()
        }

    }
}

Then to display these workouts on the feed page view in my app I fetch all the workouts in the user-feed collection on firestore with this function:

//FETCH WORKOUTS SAVED BY THE USER
func fetchFavoriteWorkouts() {

    guard let currentUid = AuthViewModel.shared.userSession?.uid else { return }

    COLLECTION_USERS.document(currentUid).collection("user-feed").addSnapshotListener { snapshot, _ in
        guard let workoutIDs = snapshot?.documents.map({ $0.documentID }) else { return }
        
        //THIS MAY CAUSE AN UNNECCESSARY AMOUNT OF WRITES TO THE APP
        self.workouts.removeAll()

        workoutIDs.forEach { id in
            COLLECTION_WORKOUTS.document(id).addSnapshotListener { snapshot, _ in
                guard let workout = try? snapshot?.data(as: Workout.self) else { return }
                self.workouts.append(workout)
                print("\(workoutIDs)")
            }
        }
    }
}

This is what the firestore collection looks like for user-feed. It adds workout ID documents to the collection that match up with workouts posting by the trainer you just favorited:

Firestore structure

This is working properly in a sense that when you favorite a trainer account it correctly adds multiple documents to the user-feed collection which correspond to workout IDs posted by the trainer you just favorited, however, when you favorite a trainer account the app just closes (not really crashes), and then when you re-open the app the user-feed correctly displays the workouts from trainers you have favorited.

Is there anything in my code that may be causing this random app close when you favorite a trainer?

I understand that this code may not be the most efficient, but I am really not focused on fixing that at the moment, just want to fix the random app close out.

Edit: The crash only happens when I favorite a trainer that has multiple workouts posted. So I guess something causes the crash when I add multiple documents to a collection at once? Because if I favorite a trainer that only has one workout then it adds that workout to my feed without crashing at all.

CodePudding user response：

the problem is caused by the listener getting called each time a workout is added to workout list and adding duplicated values to the list .

change addSnapshotListener to getDocuments fetchFavoriteWorkouts() and call this fetch function inside .onAppear() in feed View