Firestore async issue

Question

I'm calling a Firestore query that does come back, but I need to ensure completion before moving on with the rest of the code. So I need a completion handler...but for the life of me I can't seem to code it.

// get user info from db
    func getUser() async {
        self.db.collection("userSetting").getDocuments() { (querySnapshot, err) in
            if let err = err {
                print("Error getting documents: \(err)")
            } else {
                for document in querySnapshot!.documents {
                    let userTrust = document.data()["userTrust"] as! String
                    let userGrade = document.data()["userGrade"] as! String
                    let userDisclaimer = document.data()["userDisclaimer"] as! String
                    
                    var row = [String]()
                    row.append(userTrust)
                    row.append(userGrade)
                    row.append(userDisclaimer)
                    
                    self.userArray.append(row)
                    
                    // set google firebase analytics user info
                    self.userTrustInfo = userTrust
                    self.userGradeInfo = userGrade

                }
            }
            
        }
    }

Called by:

internal func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        
        FirebaseApp.configure()
        db = Firestore.firestore()
        Database.database().isPersistenceEnabled = true

        Task {
            do {
                let userInfo = await getUser()
            }
        } return true }

I used a Task as didFinishLauncingWithOptions is synchronous and not asynchronous

However, the getUser() still isn't completed before didFinishLauncingWithOptions moves on.

I need the data from getUser as the very next step uses the data in the array, and without it I get an 'out of bounds exception' as the array is still empty.

Also tried using dispatch group within the func getUser(). Again with no joy.

Finally tried a completion handler:

func getUser(completion: @escaping (Bool) -> Void) {

        self.db.collection("userSetting").getDocuments() { (querySnapshot, err) in
            if let err = err {
                print("Error getting documents: \(err)")
            } else {

                for document in querySnapshot!.documents {

                    let userTrust = document.data()["userTrust"] as! String
                    let userGrade = document.data()["userGrade"] as! String
                    let userDisclaimer = document.data()["userDisclaimer"] as! String
                    
                    var row = [String]()
                    row.append(userTrust)
                    row.append(userGrade)
                    row.append(userDisclaimer)
                    
                    self.userArray.append(row)
                    
                    // set google firebase analytics user info
                    self.userTrustInfo = userTrust
                    self.userGradeInfo = userGrade
                    
                    completion(true)
                    }
                
                }
            }
        
        }

Nothing works. The getUser call isn't completed before the code moves on. Can someone please help. I've searched multiple times, looked at all linked answers but I can not make this work.I'm clearly missing something easy, please help

Answer 1

read this post: Waiting for data to be loaded on app startup.

It explains why you should never wait for data before returning from function application(_:didFinishLaunchingWithOptions).

To achieve what you need, you could use your first ViewController as a sort of splashscreen (that only shows an image or an activity indicator) and call the function getUser(completion:) in the viewDidLoad() method the ViewController.

Example:

class FirstViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        MyFirestoreDatabaseManager.shared.getUser() { success in
            if success {
                //TODO: Navigate to another ViewController
            } else {
                //TODO: Show an error
            }
        }
    }
}

Where obviously MyFirestoreDatabaseManager.shared is the object on which you defined the getUser(completion:) method.

(In your example, I think that you defined that function in the AppDelegate. In that case, you should mark your getUser(completion:) method and all related variables as static. Then replace MyFirestoreDatabaseManager.shared with AppDelegate).

Answer 2

Not 100% sure what you would like to accomplish as I can't see all your code, but try something similar to this, replacing Objects for what you are trying to return from the documents.

You don't want your user's data spread across multiple documents. With Firebase you pay for every document you have to get. Ideally you want all your user's settings within one firebase document. Then create a UserInfo struct that you can decode to using the library CodeableFirebase or the decoder of your choice.

// Create user struct
struct UserInfo: Codable {
    var userId: String
    var userTrust: String
    var userGrade: String
    var userDisclaimer: String
}

// get user info from db and decode using CodableFirebase
func getUser() async throws -> UserInfo {
    let doc = try await self.db.collection("users").document("userIdHere")
    let userInfo = try FirestoreDecoder().decode(UserInfo.self, from: doc.data())
    return UserInfo
}

Then you can do this...

Task {
    do {
        let userInfo = try await getUser()
        let userTrust = userInfo.userTrust
        let userGrade = userInfo.userGrade
        let userDisclaimer = userInfo.userDisclaimer
    }
}