Firebase 确保不重复记录

Question

I have this code:

public static void insertvote(String userkey, String categ, String candId) {
            DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
            DatabaseReference totalVotesRef = rootRef.child("votes").child(categ).child(candId);
            Vote vote = new Vote(userkey);
            totalVotesRef.push().setValue(vote.getVoterEmail());
    }

It is supposed to insert votes into a firebase database, in a votes collections as below:

The idea is to ensure a voter only votes once due to integrity by checking if their email exists in the votes. However, as you can see, a voter can vote twice. Is there a way I can make a function that checks whether the email exixts in the database, and if it does exist, tell the voter they cant vote twice? Thanks in advance.

Answer 1

You should use the Firebase Auth UID of the current user as the name of the child key.

String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
totalVotesRef.child(uid).setValue(vote.getVoterEmail());

Answer 2

I will give you an idea, think about it. If you use Shared Preferences, you can put every e-mail address with a boolean flag(True/False - Voted/not). Then, you can call the Shared Preferences and check the boolean value of the flag for every e-mail address. So, if it's true - don't allow him to vote.

Wish I helped :)