I am making an Android application using Firebase realtime database. When a new user registers on my app, that user's data is saved in the Firebase database.
A user has to provide the following details to register:
- Full Name
- Username
- Password
Database Structure
Whenever a new user tries to register, I have to make sure that each user's username is unique so I check the database if the username entered by the user already exists in the database or not.
To do this, I wrote the following method:
private boolean usernameExists(String username) {
DatabaseReference fdbRefer = FirebaseDatabase.getInstance().getReference("Users/"+username);
return (fdbRefer != null);
}
My logic behind this method is that if getReference method cannot find reference to the specified path, it will return null so that I can return whether fdbRefer is null or not. If fdbRefer is null, then it means that username doesn't exist in the database.
Problem
Problem with this method is that it always returns true whether the entered username exists in the database or not. Which led me to believe that fdbRefer is never null.
This brings me to my question...
Question
What does getReference method return when it can't find the specified path in the firebase database and what's the correct way to check if the username already exists in the database or not?
To check a existence of user, please use the below code:
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference userNameRef = rootRef.child("Users").child("Nick123");
ValueEventListener eventListener = new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
if(!dataSnapshot.exists()) {
//create new user
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
Log.d(TAG, databaseError.getMessage()); //Don't ignore errors!
}
};
userNameRef.addListenerForSingleValueEvent(eventListener);
You can also use a Query to achieve the same thing like this:
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
Query query = rootRef.child("Users").orderByChild("userName").equalTo("Nick123");
query.addValueEventListener(/* ... */);
This is another approach which is looping through the entire Users node but is not just using a direct reference to a single user. This option is more likely to be used when you are using as a unique identifier beteeen users the uid instead of the user name (as you do right now). So if your database structure might looks similar to this:
Firebase-root
|
--- Users
|
--- uid
|
--- userName: "Test User"
|
--- emailAddress: "[email protected]"
The second solution is the recommended one.
There is also another solution which involves youto create another node named userNames, in which you can hold only the unique user names. Please also find below the corresponding security rules:
"Users": {
"$uid": {
".write": "auth !== null && auth.uid === $uid",
".read": "auth !== null && auth.provider === 'password'",
"userName": {
".validate": "
!root.child('userNames').child(newData.val()).exists() ||
root.child('userNames').child(newData.val()).val() == $uid"
}
}
}
But since in this case, your user name is already the name of the node, I recommend you go ahead with the first one.