Firebase query (in swift) to determine if username already exists in database - ios

Question

I have very little experience with Firebase and iOS and was wondering if it was possible to create a query in Swift to find specific data in the Firebase's JSON structure.
When a user creates an account in the app, he is prompted to chose a username. When the user presses on the "Continue" button on this same screen, I would like to query the DB in real-time to determine if the username the user chose already exists or not.
I read a bunch of articles on the web but couldn't find anything that would let me achieve my goal. So far, I wrote the following code which doesn't work, but I am unable to pinpoint the source of the problem (note that username.text is the textfield where the user enters his desired username and with which the verification is made) :
FIRDatabase
.database()
.reference()
.child("username")
.queryOrderedByValue()
.queryEqual(toValue: self.username.text!)
.observeSingleEvent(of: .value, with: {(snap) in
if snap.exists(){
// Username unavailable, choose another one
} else {
// Username available, OK to keep this username
}
})
The DB structure is as follows :
{
"users" : {
USER_1_UID : {
"account" : {
"email" : "test#stackoverflow.com",
"first name" : "myFirstName",
"last name" : "myLastName",
"username" : "my.username"
}
}
USER_2_UID : {
"account" : {
"email" : "test#stackoverflow.com",
"first name" : "myFirstName2",
"last name" : "myLastName2",
"username" : "my.username2"
}
}
}
}
I am open to change my DB structure to add the "usernames" note as shown below which will contain all of the usernames registered if it can make the querying easier :
{
"users" : {
USER_1_UID : {
"account" : {
"email" : "test#stackoverflow.com",
"first name" : "myFirstName",
"last name" : "myLastName",
"username" : "my.username"
}
}
USER_2_UID : {
"account" : {
"email" : "test#stackoverflow.com",
"first name" : "myFirstName2",
"last name" : "myLastName2",
"username" : "my.username2"
}
}
}
"listOfUsernames" : {
USER_1_UID : "my.username"
USER_2_UID : "my.username2"
}
}
Any help at this point will be welcome. Thank you!

Answer 1

Your code is pretty close. Three changes:
Remove queryOrderedByValue
then, you've buried your user information too deep
USER_1_UID : {
"account" : {
"email" : "test#stackoverflow.com",
"first name" : "myFirstName",
"last name" : "myLastName",
"username" : "my.username"
}
}
Change to (remove the account node name as it's not needed)
USER_1_UID : {
"email" : "test#stackoverflow.com",
"first name" : "myFirstName",
"last name" : "myLastName",
"username" : "my.username"
}
and then you need to tell Firebase which node you are querying
so change to
let usersRef = rootRef.child("users")
let queryRef = usersRef.queryOrdered(byChild: "username")
.queryEqual(toValue: "some user name")
queryRef.observeSingleEvent(of: .value, with: { snapshot in
print(snapshot) //you need snapshot, or snap or some other var name
})
Lastly, you don't need a listOfUsernames node, your users node will work just fine.