How to check if email already exists in Firestore db - swift

Question

I have implemented Auth method for the Firestore database, but when the user tries to register with the same email, the app crash. I'd like to implement a function to check if the email already exists (if it does, fire UIAlert, otherwise if it doesn't, create a new user).
I have so far:
Auth.auth().createUser(withEmail: email, password: password) { (Result, err) in
let db = Firestore.firestore()
let docRef = db.collection("email users").document("email")
docRef.getDocument { (document, error) in
if let document = document, document.exists {
let emailAlreadyInUseAlert = UIAlertController(title: "Error", message: "Email already registered", preferredStyle: .alert)
emailAlreadyInUseAlert.addAction(UIAlertAction(title: "OK", style: .cancel, handler: nil))
self.present(emailAlreadyInUseAlert, animated: true, completion: nil)
return
} else {
let db = Firestore.firestore()
db.collection("email users").addDocument(data: [
"firstName": firstName,
"lastName": lastName,
"email": email,
"created": Timestamp(date: Date()),
"uid": Result!.user.uid
])
}
self.transitionToHome()
}
}
}
}
func transitionToHome() {
let homeViewController = storyboard?.instantiateViewController(identifier: "HomeViewController") as? HomeViewController
view.window?.rootViewController = homeViewController
view.window?.makeKeyAndVisible()
}
}
At this code the UIAlert doesn't fire, and have an error at : "uid": Result!.user.uid - Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value. When creating new user with unique email, it works as it should, the user is created.
If I change if let document = document, document.exists to if error !=nil, I get the UIAlert when the email already exist and also if it doesnt exist, the code of creating user doesnt execute.
Even tried to implement addsnapshotlistener, no luck.
Any suggestions? Thank you

Answer 1

Regarding error: it's a common practice to return success code as error code instead of setting error to nil, and google docs seems mention it as well.
The other issue is because you are forcibly unwrapping items that can legitimately be nil.
Instead, use guard to isolate any invalid cases and exit:
guard error == nil || case FirestoreErrorCode.OK = error else {
// got error; process it and
return
}
guard let result = result else {
// got no error, but no result either
// fail and
return
}
//if you are here, it means you've got no error and `result` is not nil.
Also notice that result should not be capitalized in callback:
Auth.auth().createUser(withEmail: email, password: password) { (result, err) in ...

Answer 2

You may not need a custom function to check if an email already exists as that's a default error Firebase Auth will catch and allow you to handle when a user is created.
For example, this code will catch situations where the user is attempting to use an email that already exists.
func createUser() {
let email = "test#thing.com"
Auth.auth().createUser(withEmail: email, password: "password", completion: { authResult, error in
if let x = error {
let err = x as NSError
switch err.code {
case AuthErrorCode.wrongPassword.rawValue:
print("wrong password")
case AuthErrorCode.invalidEmail.rawValue:
print("invalid email")
case AuthErrorCode.accountExistsWithDifferentCredential.rawValue:
print("accountExistsWithDifferentCredential")
case AuthErrorCode.emailAlreadyInUse.rawValue:
print("email already in use")
default:
print("unknown error: \(err.localizedDescription)")
}
return
}
let x = authResult?.user.uid
print("successfully created user: \(x)")
})
}
There's a number of Authentication Error Codes so you can handle a wide variety of errors without any special error handling.
And the AuthErrorCode API has some more useful information which is demonstrated in the answer code.