Unique usernames in Firebase - swift

Question

I have been trying to implement Chris’ answer here: Can I make Firebase use a username login process? for the Facebook login but I can’t seem to get my head around it.
So far I’ve tried to set conditions on the textField but as Firebase observer works asynchronously, the conditions to check if the username exists in the database won’t work.
let usernameString = usernameTextField.text
let uid = FIRAuth.auth()?.currentUser?.uid
ref.runTransactionBlock({ (currentData: FIRMutableData) -> FIRTransactionResult in
if var post = currentData.value as? [String : AnyObject], let uid = FIRAuth.auth()?.currentUser?.uid {
let usernamesDictionary = post["usernames"] as! NSDictionary
for (key, _) in usernamesDictionary {
if key as? String == usernameString {
print("username not available: \(key)")
}
else if usernameString == "" {
print("Uh oh! Looks like you haven't set a username yet.")
}
else if key as? String != usernameString {
print("username available: \(key)")
print("All set to go!")
let setValue: NSDictionary = [usernameString!: uid]
post["usernames"] = setValue
currentData.value = post
}
}
return FIRTransactionResult.successWithValue(currentData)
}
return FIRTransactionResult.successWithValue(currentData)
}
Then I tried creating /usernames/ node in the database and set up rules as:
{
"rules": {
"usernames": {
".read": "auth != null",
".write": "newData.val() === auth.uid && !data.exists()"
}
}
}
Now that won’t let me set any username to the database. I get confused in creating rules but my whole point is that I need a sign up flow with the username data that’s unique for each user in the database.

Answer 1

While trying every answer I found in related posts, what worked for me the easy way i.e. without making Firebase rules play a part in it or creating a separate usernames node in the database was to not put an if/else condition inside the Firebase observer but instead to use the exists() method of FIRDataSnapshot.
Now here’s the trick, while I did try only the exists() method with a simple observer but that did not help me. What I did was first query usernames in order, then match the username with queryEqualToValue to filter the query:
refUsers.queryOrderedByChild("username").queryEqualToValue(usernameString).observeSingleEventOfType(.Value , withBlock: {
snapshot in
if !snapshot.exists() {
if usernameString == "" {
self.signupErrorAlert("Uh oh!", message: "Looks like you haven't set a username yet.")
}
else {
// Update database with a unique username.
}
}
else {
self.signupErrorAlert("Uh oh!", message: "\(usernameString!) is not available. Try another username.")
}
}) { error in
print(error.localizedDescription)
}
}
This is the first time out of most of the answers here that worked for me. But for now, I don’t know if this would scale. Post your experiences and best practices. They’ll be appreciated.