Firebase check for existing user in swift - ios

Question

I have VC where by I am creating a new user and adding to firebase. The user inserts no problem into the database but I am having trouble checking if a user with the same name already exists. I have tried using various query statements within firebase but not getting any joy. Does anyone know how I can modify my code to accomplish this? here it is :-
#IBAction func submitUsername(sender: AnyObject) {
if let user = usernameTxtField.text where user != "" {
let username = DataService.ds.REF_USERS.childByAppendingPath("username")
username.observeSingleEventOfType(.Value, withBlock: { snap in
if let usernameDoesNotExist = snap.value as? NSNull {
let currentUser = DataService.ds.REF_USER_CURRENT.childByAppendingPath("username")
self.usernameTxtField.text = user
currentUser.setValue(user)
}
})
dismissViewControllerAnimated(true, completion: nil)
} else {
showAlert("Username Needed", msg: "please choose a username")
}
}
and the firebase data structure
"users" : {
"000591b6-ba88-4670-9cb7-edd79c273eab" : {
"newuser" : "added to FB",
"provider" : "password"
},
"05551c90-27fe-4969-b45d-279a72583857" : {
"newuser" : "added to FB",
"provider" : "password"
},
"0bbff1b0-681a-4fef-adc0-c4779a4b2100" : {
"provider" : "password",
"testing" : "emailtest",
"username" : "richy446"
},
"12f35e7a-2430-49b3-a287-f7b1daf6a121" : {
"newuser" : "added to FB",
"provider" : "password",
"username" : "richy445"
},
"15a45560-cc81-4c2d-bb59-b8ce6b125d68" : {
"provider" : "password",
"testing" : "emailtest",
"username" : "richy445"
},
"1c135936-6dd0-4189-bcd7-e8036e9736f9" : {
"newuser" : "added to FB",
"provider" : "password"
},
"21591e29-f083-452c-b74f-cc567cecb183" : {
"newuser" : "added to FB",
"provider" : "password"
},
"8b385aa7-0e80-426b-a385-5b3317c894d0" : {
"newuser" : "added to FB",
"provider" : "password",
"username" : "richy445"
}
}

Answer 1

There are a number of approaches to checking for duplicate data. The Firebase structure you have seems a little inconsistent so structuring it like this may be easier
"000591b6-ba88-4670-9cb7-edd79c273eab" : {
"email" : "test#test.com",
"password" : "password"
},
"05551c90-27fe-4969-b45d-279a72583857" : {
"email" : "test2#test.com",
"password" : "password"
},
1) Let Firebase do the work for you.
When creating a user, Firebase will return an error if the username (email) already exists. Using this method will prevent random data being written to your firebase until they account is created in Firebase.
myRootRef.createUser(email, password: pw, withValueCompletionBlock: { error, result in
if error != nil {
self.errMsgField.stringValue = "email/username in use, try again"
} else {
let uid = result["uid"] as! String //the uid of the new user
print("user created as \(uid)")
self.storedDataInUserNode(email, password:pw)
self.authUserWithAuthData( email, password: pw ) //auth the user
// and proceed in starting up the app
}
})
2) Checking for existing data in Firebase.
While the first method stops data from being written in the first place, if you want to check for duplicate data in general, here's a pattern:
let userName = the userName or email the user entered
let usersRef = Firebase(url:"https://test.firebaseio.com/users")
usersRef.queryOrderedByChild("email").queryEqualToValue("\(userName!)")
.observeSingleEventOfType(.Value, withBlock: { snapshot in
if ( snapshot.value is NSNull ) {
print("not found)") //didnt find it, ok to proceed
} else {
print(snapshot.value) //found it, stop!
}
}

Answer 2

There's a method on DataSnapshot named .exists() that you can you can call like this.
Updated for Swift 4.
struct ModelUser {
var id: String
var name: String
init(data: DataSnapshot) {
// do init stuff
}
}
func isUserRegistered(with id: String, completion: #escaping (_ exists: Bool, _ user: ModelUser?) -> ()) {
DatabaseReference.users.child(id).observeSingleEvent(of: .value) { (snapshot) in
if snapshot.exists() {
// user is already in our database
completion(true, ModelUser(data: snapshot))
} else {
// not in database
completion(false, nil)
}
}
}