Remove anonymous user from Auth database

问题

I'm using Firebase database and little confused with next situation.

Let's imagine i have todo app. I use standard Firebase Auth system for sync items between user devices. But in other case user could work anonymously without synchronization.

Step 1:

User launch app first time, and in AppDelegate i created Anonymous user:

FIRAuth.auth()?.addStateDidChangeListener { auth, user in
  if let _user = user {
    if _user.isAnonymous {
        print("User logged in as anonymous. Saving uid to user defaults storage.")
        UserDefaults.standard.setValue(_user.uid, forKey: "uid")
    } else {
         print("User logged in with email: \(_user.email)")
    }
  } else {
     FIRAuth.auth()?.signInAnonymously() { (user, error) in
        if let _error = error {
           print("Anonymous signIn error: \(_error)")
        }
     }
  }
}

Step 2:

This anonymous user created few todo items and decided signUp:

let credential = FIREmailPasswordAuthProvider.credential(withEmail: emailField.text!, password: passwordField.text!)
FIRAuth.auth()?.currentUser?.link(with: credential, completion: { user, error in
    if error == nil {
        FIRAuth.auth()!.signIn(withEmail: emailField.text!,
                                       password: passwordField.text!)
     }
 })

So i have modified previous code and change owner of created todo items:

if let prevUserUID = UserDefaults.standard.string(forKey: "uid"), prevUserUID != _user.uid {
    FIRDatabase.database().reference().child("todo-items").queryOrdered(byChild: "user").queryEqual(toValue: prevUserUID).observe(.value, with: { snapshot in
    for item in snapshot.children {
        var todoItem = TodoItem(snapshot: item as! FIRDataSnapshot)
        todoItem.user = _user.uid
        todoItem.ref?.setValue(todoItem.toAnyObject())
    }
  })
  print("Data migrated.")
}

Ok everything works. But, now user logged out. An i created new anonymous user. Then he login again and i merge data. But i can't link account, because i already did it before. And i can't delete anonymous user from Auth database(my question). And we get zombie! unused anonymous account. And if user will log in/log out 1000 times we get 1000 anonymous accounts.

回答1:

When you link the credential with the currentUser you are logged already, don't need for:

FIRAuth.auth()!.signIn

You keep the UID of the anonymous user.

If user already have an account, in this case you need to:

currentUser.delete()

And then logIn with the credentials provided

来源：https://stackoverflow.com/questions/41555145/remove-anonymous-user-from-auth-database