SwiftUI: Check if Firebase RealtimeDatabase has a specific Child the register the value or return error - swift

Question

I am currently building an app with an account system.
Firebase is very new to me, that's why I watched a lot of tutorials, and now its working fine.
I want to implement that the user can choose a unique username at the registration. My problem is, I really don't know how to check if this name is already taken.
I found some code for that, but that's not working, I will show you the code for the RegistrationService file.
I hope someone can explain to me how to implement this username verification. It should return an error if the username is already taken and do continue the registration if its a valid username.
Thank you!
import Combine
import Firebase
import FirebaseDatabase
import Foundation
enum RegistrationKeys: String {
case firstName
case lastname
case info
case username
}
protocol RegisterService {
func register(with details: RegistrationDetails) -> AnyPublisher<Void, Error>
}
final class RegisterServiceImpl: RegisterService {
func register(with details: RegistrationDetails) -> AnyPublisher<Void, Error> {
Deferred {
Future { promise in
Auth.auth()
.createUser(
withEmail: details.email,
password: details.password
) { res, error in
if let err = error {
promise(.failure(err))
} else {
// Success on User creation
if let uid = res?.user.uid {
let values =
[
RegistrationKeys.firstName.rawValue: details.firstName,
RegistrationKeys.lastname.rawValue: details.lastName,
RegistrationKeys.info.rawValue: details.info,
] as [String: Any]
let db = Database.database(url: "theurl")
Database.database(url: "the url")
.reference()
.child("usernames")
.child("\([RegistrationKeys.info.rawValue: details.username] as [String : Any])")
// here should be the check and then continue if its valid
db
.reference()
.child("users")
.child(uid)
.updateChildValues(values) { error, ref in
if let err = error {
promise(.failure(err))
} else {
promise(.success(()))
}
}
} else {
promise(.failure(NSError(domain: "Invalid user ID", code: 0, userInfo: nil)))
}
}
}
}
}
.receive(on: RunLoop.main)
.eraseToAnyPublisher()
}
}

Answer 1

I can see two possibilities to solve your problem:
If the e-mail can serve as the username
Firebase authentication already sends back an error message in case the e-mail (the one used when creating the user) already exists. If the e-mail passed in the following function is not unique, an error will be thrown:
Auth.auth()
.createUser(
withEmail: details.email,
password: details.password
) { res, error in
if let err = error {
promise(.failure(err))
If an additional username besides the e-mail is required
If you need usernames in addition to the e-mails, you can store them under a node "usernames", like we see in your example. Personally, I would hash them instead of storing them plain.
The structure could simply be:
{
usernames: {
username_1: true,
username_2: true,
...
username_n: true
}
}
The example below checks to see if a new username exists and stores the result in the variable isUsernameTaken:
let db = Database.database(url: "the url").reference()
let newUsername = "seeIfItIsTaken"
db.child("usernames").child(newUsername).getData() { error, snapshot in
guard error == nil else {
print("Found error \(error)")
return
}
let isUsernameTaken = snapshot.exists()
}