How to check if an email exists in Firebase Authentication?-CodePudding

I am trying to check if an email already exists in Firebase authentication, but I can find something for Java. I am trying to do something like searching in a list of emails and if that email is not in the database (emailNotExistsInDatabase(email)), then continue.

CodePudding user response：

There is no method inside the FirebaseAuth class that can help you check the existence of a user based on an email address. If you need that functionality you have to create it yourself. This means that when a user signs in for the first time into your app, then save user data in Firestore using a schema that looks like this:

db
|
--- users (collection)
     |
     --- $uid (document)
          |
          --- email: "[email protected]"

To check if a user with the [email protected] already exists, then you have to perform a query that looks like this in Java:

FirebaseFirestore db = FirebaseFirestore.getInstance();
Query queryByEmail = db.collection("users").whereEqualTo("email", "[email protected]");
queryByEmail.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
    @Override
    public void onComplete(@NonNull Task<QuerySnapshot> task) {
        if (task.isSuccessful()) {
            for (QueryDocumentSnapshot document : task.getResult()) {
                if (document.exists()) {
                    Log.d(TAG, "User already exists.");
                } else {
                    Log.d(TAG, "User doesn't exist.");
                }
            }
        } else {
            Log.d(TAG, task.getException().getMessage()); //Never ignore potential errors!
        }
    }
});

Another solution would be to use Query#count() method:

queryByEmail.count();

If the result is > 0 then it means that the user already exists, otherwise it doesn't exist.

CodePudding user response：

In addition to the very complete response from Alex, another possible approach is to use a Callable Cloud Function that you call from your app.

Since we use the Admin SDK in Cloud Functions you can use the getUserByEmail() method.

The function would look like:

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();

exports.checkEmailExists = functions.https.onCall((data, context) => {

    return admin.auth()
        .getUserByEmail(data.email)
        .then((userRecord) => {
            return { emailExists: true }
        })
        .catch((error) => {
            throw new functions.https.HttpsError('invalid-argument', "email doesn't exist");
        });

});

With this approach you don't need a specific Firestore collection. The Admin SDK will directly query the Auth service.

Look at the doc for instructions on how to call the Callable Cloud Function from your app.

Note that the above approach is valid if you want to check if a user exists from an application (e.g. an Android app).

If you already use the Admin SDK from a Java based server, you just have to use the getUserByEmail() method in your server code.