Annoying issue regarding indexOn in Firebase rules - swift

Question

I have read practically every StackOverflow answer and none of them worked for my scenario since this is a frequent issue. My Xcode console is giving a very common warning when querying for data in Firebase. That warning is Using an unspecified index. Your data will be downloaded and filtered on the client. Consider adding ".indexOn": "username" at /users to your security rules for better performance
What I have tried was to first read the Firebase documentation understanding exactly what I am doing along with other answers as stated such as Why does this Firebase ".indexOn" not work?. Below, I have provided my security rules doing exactly as the message prompt; adding indexOn at /users but to no success. I have also provided my database users node and one function below.
{
"rules": {
".read": true,
".write": true,
"users":{
".indexOn": "username"
}
}
}
My Firebase database at /users in JSON format
"users":{
"5LYUynelLTcL8Bg9WNWGXV34YIq2" {
"email": "user1#gmail.com"
"username": "user1"
}
"9srk307kzxOW7j6dNmMaac9eYPu2" {
"email": "user2#gmail.com"
"username": "user2"
}
My function that I use in Swift
let ref = Database.database().reference().child("users").queryOrdered(byChild: "username").queryEqual(toValue: passedInFriendString)
ref.observeSingleEvent(of: .value) { (snapshot) in
print(snapshot)
}
I'm not sure where else to turn to. Any insight on if this is even the correct format to query for what I want would be great!

Answer 1

I solved it!
The thing I did not realize was that the above code in my question DOES print the snapshot successfully after adding the appropriate index definition on /users. My issue was realizing you need to loop through the snapshot if you want to further access data of the username snapshot I was querying for accordingly. That would look something like this
let ref = Database.database().reference().child("users").queryOrdered(byChild: "username").queryEqual(toValue: passedInFriendString)
ref.observeSingleEvent(of: .value) { (snapshot) in
for child in snapshot.children {
guard let snap = child as? DataSnapshot else {return}
if snap.hasChild("email") {
print("It has an email")
}
}
}
Thanks to Frank above for guiding me and confirming that I was on the right track. I'm happy to have learned something new and super efficient whenever I need to grab data.