Firebase get value from database - firebase

Question

The question is: How to take the uid row when you only know the user his username? for example, you only know 'senneken' and you want to know the uid of 'senneken'
Extra information:
My user database looks like this
I want to add friends to users. I can check if the user exists for them by doing
searchButton.addEventListener('click', function (event) {
event.preventDefault();
username = searchUsername.value;
var ref = firebase.database().ref('users').orderByChild("username").equalTo(username).once("value", snapshot => {
const userData = snapshot.val();
if (userData) {
console.log("Username " + username + " was found");
} else {
console.log("No user found");
}
But now I want to add the users UID in my database
And I can add the friends username by doing
addFriendButton.addEventListener('click', function (event) {
firebase.auth().onAuthStateChanged(function (user) {
if (user) {
var ref = firebase.database().ref("users").child(user.uid).child("friends").push({
username: username
})
}
});
});
Because I use push there is always a random ID generated under friends but I would like to take the UID from the user that I want to add and put that under my friends (instead of the random UID)

Answer 1

In this case the collection of friends seems like a set: each specific UID can either be in there, or it cannot be in there. It cannot be in there more than once, and order seems to not matter. The solution is to not use a push ID, but model it as a set like this:
friends
uid1
uid2: true
uid3: true
This way you can simply set a user as a friend with:
firebase.database().ref("friends").child(user.uid).child(username).set(true)
You might notice that I also turned the collections of friends into a top-level collection. Nesting information about friends under other profile information about a user is an anti-pattern, which makes it hard to secure data, leads to downloading more data than is needed, and in general is not recommended by Firebase experts.