How to add new child in Firebase database Android

Question

I'm trying to add a new child using the DatabaseReference in my Firebase Android app. I'm doing:

DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference() 
mDatabase.child("childToAdd").setValue(1);

I can do this with a regular Firebase Reference as it would add the child to the database if it isn't there.
How could I go about doing this with DatabaseReference?

Edit: Thanks for all the suggestions but I'm having issues with the following code. When it enters the if block it does not push the data onto the database.

https://gist.github.com/rounaksalim95/a5cba332400c6caf8320f15b0cbf06e8

When I try this with the old Firebase reference I get error code 11 (User code called from firebase runloop) and with the new database reference I get error code -3 (PermissionDenied even though I have no security rules).

Update:

I got it to do what I wanted to using a single value event listener:

Firebase userRef = new Firebase(BASEURL + "userData");

userRef.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        if (dataSnapshot.child(user.getUid()).getValue() == null) {
            userRef.child(user.getUid()).setValue(1);
        }
    }

    @Override
    public void onCancelled(FirebaseError firebaseError) {

    }
});  

However database reference doesn't let me add values like this.

Answer 1

You'll need to call push() to generate a unique key for the new data:

DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference() 
mDatabase.push().setValue(1);

This will append the new value at the end of the list.

By combining the push() and child() methods, you can create multiple lists of children in the database:

mDatabase.child("numbers").push().setValue(1);
mDatabase.child("numbers").push().setValue(53);
mDatabase.child("numbers").push().setValue(42);

mDatabase.child("letters").push().setValue("a");
mDatabase.child("letters").push().setValue("z");
mDatabase.child("letters").push().setValue("c");

See the section append to a list of data in the Firebase documentation.

Answer 2

Another post mentioned to check your gradle app file to ensure you have the latest version of the Firebase as follows:

compile 'com.google.firebase:firebase-core:10.0.1'
compile 'com.google.firebase:firebase-database:10.0.1'

I think this should fix many issues that could arise from using older versions.

I hope this helps.