Facebook login using Firebase - Swift iOS - ios

Question

I'm implementing login with Facebook using Firebase, I have this code which searches my database after a successful facebook authentication for the email if exists in database and logs in the app if found, I want to direct the user to registration view controller if not found but its not working since this method is asynchronous. I appreciate if anyone can help. Here is my code :
func getFacebookUserInfo() {
if(FBSDKAccessToken.current() != nil){
let graphRequest = FBSDKGraphRequest(graphPath: "me", parameters: ["fields" : "id,name,gender,email,education"])
let connection = FBSDKGraphRequestConnection()
connection.add(graphRequest, completionHandler: { (connection, result, error) -> Void in
let data = result as! [String : AnyObject]
let email = data["email"] as? String
let emailRef = FIRDatabase.database().reference().child("usernameEmailLink")
emailRef.queryOrderedByValue().observe(.childAdded, with: { snapshot in
if let snapshotValue = snapshot.value as? [String: AnyObject] {
for (key, value) in snapshotValue {
if(value as? String == email){
self.stringMode = snapshotValue["mode"]! as! String
self.username = key
self.parseUserInfoFromJSON()
return
}
}
}
})
})
connection.start()
}
}
Thank you.

Answer 1

The registration/existence of the user in Firebase should probably be determined before the graphRequest code in the question.
Most importantly, (and this is critical), email addresses are dynamic so they should not be used to verify if a user exists. i.e. user with email address of 'leroy#gmail.com' updates his email to 'leroy.j#gmail.com'. If emails are used to verify registration, it can totally break if that email changes.
Please use Firebase uid's for that purpose as they are static and unique.
Since we only have a small snippet of code, we don't know the exact sequence being used. This answer is pseudo-code to outline a possible sequence.
We assume that by 'registered' it means that the user has gone through some kind of app registration sequence and the user has been created (and now exists/is registered) in Firebase.
In general there would be a login button and a delegate method to handle the actual login action.
The user enters their login and taps the login button
func loginButton(loginButton: FBSDKLoginButton!,
didCompleteWithResult result: FBSDKLoginManagerLoginResult!,
error: NSError?) {
Firebase can then get the credentials for that user (see Firebase doc quote below)
let credential = FIRFacebookAuthProvider.credential(withAccessToken: FBSDKAccessToken.current().tokenString)
At that point, sign in the user and check to see if they are registered (exist) in the Firebase user node.
FIRAuth.auth()?.signIn(with: credential) { (user, error) in
if let error = error { //failed due to an error
return
}
let uid = user.uid //the firebase uid
let thisUserRef = userRef.child(uid) //a reference to the user node
//check to see if the user exists in firebase (i.e. is Registered)
thisUserRef.observeSingleEvent(of: .value, with: { (snapshot) in
//if snapshot exists
//then the user is already 'registered' in the user node
// so continue the app with a registered user
//if not, then need to have the user go through a registration sequence and
// then create the user (make them registered) in the user node
doRegisterUser(user)
})
func doRegisterUser(user: FIRUser) {
//get what you need from the user to register them
// and write it to the users node. This could be from additional
// questions or from their Facebook graph, as in the code in the
// question
//for this example, we'll just write their email address
let email = user.email
let dict = ["email": email]
//create a child node in the users node with a parent of uid
// and a child of email: their email
thisUserRef.setValue(node)
//next time the user logs in via FB authentication, their user node
// will be found as they are now a 'registered' user
}
From the Firebase docs
After a user signs in for the first time, a new user account is
created and linked to the credentials—that is, the user name and
password, or auth provider information—the user signed in with. This
new account is stored as part of your Firebase project, and can be
used to identify a user across every app in your project, regardless
of how the user signs in.
As I mentioned, this is very pseudo code but offers a possible sequence for a solution.