Check If An Email Exists Before Creating A User Firebase Android

So the issue I am having is I have a registration form in which users enter information (which also contains an email). I have an onClick method called public void onCreateAccount(

Solution 1:

Have an index on the email field. Then you can do a query to find by email.

That will improve performance as no need to loop through the children.

Something like:

orderByChild('email').equalTo(email).once('value').exist();

Solution 2:

Data is loaded from Firebase asynchronously, which makes it impossible to have a method like boolean validateEmail(String email) on Android. Loading data from the database would have to be a blocking operation to enable such a method, and Android doesn't allow blocking operations (as it would leave the phone inoperable).

So instead, you have to *either( move the code to create the user intovalidateEmailor pass in a custom interface that you then call once the result from the database is back. The code for that last one is below.

First we'll create a custom interface that you can implement anywhere where you need to check if a user already exists.

publicinterfaceUserExistsCallback {
  voidonCallback(boolean value);
}

This interface can be as specific or generic as you want. It's very similar to Firebase's ValueEventListener, but this interface is just for your own use.

With this interface, we can define the validateEmail method like this:

privatevoidvalidateEmail(String email, final UserExistsCallback callback) {
   isValid = true; 
   databaseUser.orderByChild("email").equalTo(emailUserEntered)
       .addListenerForSingleValueEvent(newValueEventListener() {
           @OverridepublicvoidonDataChange(@NonNull DataSnapshot dataSnapshot) {
               callback.onCallback(dataSnapshot.exists())
           }

           @OverridepublicvoidonCancelled(@NonNull DatabaseError databaseError) {
               throw databaseError.toException();
           }
       });
}

And then invoke it from onCreateAccount like this:

publicvoidonCreateAccount(View view){
   Stringemail= etEmail.getText().toString().trim();

   validateEmail(email), newUserExistsCallback() {
      publicvoidonCallback(boolean exists) {
         if (!exists) {
            Stringid= databaseUser.push().getKey();
            Useruser=newUser(id, email);
            databaseUser.child(user.getId()).setValue(user);
            Intentintent=newIntent(getApplicationContext(), LoginActivity.class);
            intent.putExtra("isCreateAccount", true);
            startActivityForResult (intent,0);
         }
      })
   }
}

Also see many of the (linked) answers below:

• getContactsFromFirebase() method return an empty list
• Setting Singleton property value in Firebase Listener
• more questions about async loading

Solution 3:

Stopping the user from logging in if such email exists should be simple and you may use a code like this to do so:

DatabaseReferencedatabaseReference= FirebaseDatabase.getInstance().getReference().child("User");

boolean flag=false;

databaseReference.orderByChild("email").equalTo(emailUserEntered).addListenerForSingleValueEvent(newValueEventListener() {
                                @OverridepublicvoidonDataChange(@NonNull DataSnapshot dataSnapshot) {
                                    if(dataSnapshot.exists())
                                       flag=true;

                                }

                                @OverridepublicvoidonCancelled(@NonNull DatabaseError databaseError) {

                                }
                            });
        return flag;                    

But if you want the user to be stopped from writing an email which is in database in mid-way, without authentication, it would be pretty difficult.

You'd have to run a check through the database letter by letter and not only this would decrease efficiency, it would be not so good looking at the end.

EDIT:

Data is loaded asynchronously from Firebase so you should be placing something like this right inside the if(dataSnapshot.exists()) to avoid the issue you're facing right now.

if(validateEmail(email)){
      Stringid= databaseUser.push().getKey();
        Useruser=newUser(id, email);
        databaseUser.child(user.getId()).setValue(user);
        Intentintent=newIntent(getApplicationContext(), LoginActivity.class);
        intent.putExtra("isCreateAccount", true);
        startActivityForResult (intent,0);
   }

else
  Toast(YourActivity.this, "Email already exists", LENGTH_LONG).show();

Solution 4:

This method is for auth only: firebase.auth().fetchProvidersForEmail("emailaddress@gmail.com")