Choosing a KEY for an object store - firebase

Question

O., this may be a relatively simple question, but it's one that I couldn't figure out (both by testing code and googling).
I have Simple Login with Email/Password enabled, and so when they login, the email used will be converted into a md5_hash.
I've created a "Users" object store, which currently looks like this:
users
|____ Bob
|__ md5_hash: 8120jf283
|__ username: Bob
|____ Alice
|__ md5_hash: 2938njv29
|__ username: Alice
|____ Chris
|__ md5_hash: 230948mv2
|__ username: Chris
My question is: How can I change the "schema" so that it stores the users by their md5_hash, instead of by their username? You can see above that it's storing the users by Bob, Alice, and Chris. It would work better for me if I could store them by their md5_hash so that it would like something like this:
Users
|___ 02938492
|__ md5_hash: 02938492
|__ username: Bob
Here's the code that I'm using to create a user and $save it into the Firebase database:
var ref = new Firebase(FIREBASE_URL + 'users');
var users = $firebase(ref);
function(authUser, username) {
users[username] = {
md5_hash: authUser.md5_hash,
username: username,
$priority: authUser.uid
};
users.$save(username).then(function() {
*do something here in callback*
});
I've tried 2 different things that didn't work. I tried using
users[authUser.md5_hash] = {...};
and I also tried
users.$save(authUser.md5_hash)
Neither of these work. Nothing gets saved to the Firebase database. It's perplexing to me because I'm almost 100% sure that it's one of those 2 parts that determines how the key is saved to firebase, but it doesn't do anything.
ULTIMATELY, what I'm trying to do is be able to "grab" the username value after a person logs in. I will be displaying their username on a navbar in a kind of "welcome Bob" fashion. However, when a user logs in, there is not yet any correlation between their md5_hash and their username. I have to be able to grab the username from the "users" table, and because I don't know their username, and the "users" table is currently indexed or keyed by their username, I have no way to get it...
A quick design question as well (if you have time):
Also, this doesn't have to do with the above question, but it's somewhat related. Just a quick question about designing my firebase "schema". If you have time, it'd be great if you could take a quick read below:
As I mentioned before, I'm using Simple Login with email/password. When a user logs in, I have access to the md5_hash of their email. Thus, to associate other user information with that login, I've created the "User table". I'm trying to connect the Login/Authentication with the said table using the md5_hash (because this is unique to each user), and then store other useful user data in it such as username, age, etc.
Is this how one would design their firebase schema? I'm used to using some sort of GUID or index in SQL, and I figured that since an md5_hash is unique, I could similarly use it to "index" my firebase users table. I just don't know if doing it this way will cause some problems in the future.
Thank you very much for your time. Any help or advice on this would be much appreciated! :)

Answer 1

With Simple Login, the user is created with a unique id:
var fbRef = new Firebase(URL);
var auth = new FirebaseSimpleLogin(fbRef);
auth.createUser(email, password, function(error, user) {
if( error ) throw error;
console.log('unique id', user.uid);
});
You can utilize that for your unique identifier. If that is insufficient, you can obtain a unique ID from the Firebase push() command:
var fbRef = new Firebase(URL);
var uniqueId = fbRef.push().name();
fbRef.child('users/'+fbRef).set(userData);
// or even shorter
var uniqueId = fbRef.push(userData).name();
With AngularFire, you can simply call $add instead of $save to create unique ids:
var users = $firebase(fbRef);
users.$add( userData ).then(function(ref) {
console.log('unique id', ref.name());
});