如何检查 childByAutoID() 是否已存在于 Firebase 实时数据库中？

Question

I am logging my users in with the Facebook and Google sign-in protocols. I am able to store these users by doing:

 let firebaseID = Auth.auth().currentUser?.uid
    let userID = user.userID
    let fullName = user.profile.name
    let email = user.profile.email
    let provider = "Google"
    guard let authentication = user.authentication else {return}
    let credential = GoogleAuthProvider.credential(withIDToken: authentication.idToken, accessToken: authentication.accessToken)
    Auth.auth().signInAndRetrieveData(with: credential) { (authResult, error) in
            if let error = error {
                print("Failed to create Firebase User with Google: ", error)
                return        
            }
            print("Successful creation of Firebase User with Google")
            let databaseRef = Database.database().reference()
            let key = databaseRef.child("node").childByAutoId().key
            let userInfo = ["UID": userID,
                            "Full Name": fullName,
                            "Email": email,
                            "Provider": provider]
            let childUpdates = ["/Users/\(key)/": userInfo]           
    databaseRef.updateChildValues(childUpdates)

Every time I sign in, even with the same credentials a new user is created with the same sign in user. How can I prevent a new instance from being created if a particular user has logged in before.

Answer 1

you should use:

let childUpdates = ["/Users/\(userID)/": userInfo] 

and so that the optional does not appear you should put it like this:

let key = databaseRef.child("node").childByAutoId().key ?? ""    

or unwrap it if you want to catch/prevent nil

let key = databaseRef.child("node").childByAutoId().key!

However, since the user id does not change when the same user enters new information, and you are using the autokey for every time the user enters, a new child is being created every time.

Answer 2

You should check if user is already registered or no after signInAndRetrieveData :

Auth.auth().signInAndRetrieveData(with: credential) { (authResult, error) in
    if let error = error {
        return
    }

    if(isNewUser()) {
        // create new user in Firebase
    }
    else {
        // continue and skip creating user ..
    }
}