I am attempting to have my program check for unique usernames. My problem right now is that it will return before completing. I understand since this is async and happening in the background; however, I have attempted using DispatchGroups and semaphores and non of which are working. This is in swift and any help would be appreciated. I am fairly new when it comes to Firestore.

func checkUsernames(_ user: String) {
    let docRef = db.collection("userRI").document(user)
    
    docRef.getDocument { (document, error) in
        if let document = document, document.exists {
            self.uniqueUser = false
            print("does exist")
        } else {
            self.uniqueUser = true
            print("does not exist \(self.uniqueUser)")
        }
    }
}

CodePudding user response：

docRef.getDocument() is asynchronous and returns immediate before the query is complete. The callback will be invoked some time later. That means your function will return before uniqueUser has a value.

The idea to fix is to consider an escaping callback to pass the value around.

func checkUsernames(_ user: String, completion: @escaping (_ uniqueUser: Bool) -> Void) {
    let docRef = db.collection("userRI").document(user)
    
    docRef.getDocument { (document, error) in
        if let document = document, document.exists {
            completion(false)
            print("does exist")
        } else {
            completion(true)
            print("does not exist \(self.uniqueUser)")
        }
    }
}