Sign up still successful even though username is taken - swift

Question

I want to create a system where the user can't sign up if the username is already taken by others. However, this seems to not work as even though the username is taken, the sign up process is still completed.
I am doing this by retrieving every username from Firebase and running it through it see if the username entered by the user is already used. If it is, it should stop the sign up process and tell user to enter another username.
Code:
let ref = Database.database().reference(fromURL: "https://heytest.firebaseio.com/")
let usernamesRef = ref.child("users")
usernamesRef.observeSingleEvent(of: .value, with: { (snapshot) in
let con = snapshot.value as! [String:[String:Any]]
var usernamesArray = [String]()
Array(con.keys).forEach {
if let res = con[$0] , let username = res["username"] as? String {
usernamesArray.append(username)
}
}
for storedUsername in usernamesArray {
if storedUsername == self.usernameTextField.text! {
self.usernameVerified = false
self.usernameLabel.textColor = UIColor.red
self.usernameLabel.text = "USERNAME TAKEN"
self.usernameTextField.layer.addBorder(edge: UIRectEdge.bottom, color: UIColor.red, thickness: 1.5)
return
}
}
}) { (error) in
print(error.localizedDescription)
}
print("TEST")
self.usernameVerified = true
print(self.usernameVerified)
self.usernameTextField.layer.addBorder(edge: UIRectEdge.bottom, color: UIColor.black, thickness: 1.5)
self.usernameLabel.textColor = UIColor.black
self.usernameLabel.text = "USERNAME"
On sign in button clicked:
#IBAction func onSignUp(_ sender: Any) {
print("Sign Up pressed")
isValidUsername(username: usernameTextField.text!)
print("[SIGN UP] - Username: \(usernameVerified)")
isValidEmail(email: emailTextField.text!)
print("[SIGN UP] - Email: \(emailVerified)")
isValidPassword(password: passwordTextField.text!)
print("[SIGN UP] - Password: \(passwordVerified)")
if passwordVerified && emailVerified && usernameVerified {
Auth.auth().createUser(withEmail: emailTextField.text!, password: passwordTextField.text!) { (authResult, error) in
if error != nil {
self.errorLabel.alpha = 1
self.errorLabel.text = error?.localizedDescription
self.shake(viewToShake: self.errorLabel)
return
}
guard let user = authResult?.user else {
return
}
//Successfully Authenticated User
let ref = Database.database().reference(fromURL: "https://heytest.firebaseio.com/")
let usersReference = ref.child("users").child(user.uid)
let values = ["username": self.usernameTextField.text!, "email": self.emailTextField.text!, "games-played": "0"]
usersReference.updateChildValues(values, withCompletionBlock: { (err, ref) in
if err != nil {
print(err!)
return
}
//Successfully registered user's data to database
print("[SIGN UP] - Successfully Signed Up")
self.errorLabel.alpha = 0
self.present((self.storyboard?.instantiateViewController(withIdentifier: "TabBarViewController"))!, animated: false, completion: nil)
})
}
} else {
errorLabel.alpha = 1
shake(viewToShake: errorLabel)
print("Password/Email/Username verification not complete!")
print("[SIGN UP] - Password: \(passwordVerified)")
print("[SIGN UP] - Username: \(usernameVerified)")
print("[SIGN UP] - Email: \(emailVerified)")
}
}

Answer 1

I think it will be easier for you to see if any matches are thrown from firebase for a specific userName.
let reference = Database.database().reference()
reference.child("users").queryOrdered(byChild: "username").queryEqual(toValue: "yourNewUserName").observeSingleEvent(of: .value) { (snapshot) in
// if there is data in the snapshot reject the registration else allow it
}
Otherwise you are downloading way too much data to the client. If you grow on users it will also take forever to download.

Answer 2

I am doing this by retrieving every username from Firebase and running it through it see if the username entered by the user is already used.
IMHO this is not the right approach, the logic should be handled server side. Imagine if you have 1 million user this will never work.