Firebase: Detecting if data exists. This snippet detects if a user ID is already taken

firebase_detect_data.js

function go() {
  var userId = prompt('Username?', 'Guest');
  checkIfUserExists(userId);
}

var USERS_LOCATION = 'https://SampleChat.firebaseIO-demo.com/users';

function userExistsCallback(userId, exists) {
  if (exists) {
    alert('user ' + userId + ' exists!');
  } else {
    alert('user ' + userId + ' does not exist!');
  }
}

// Tests to see if /users/<userId> has any data. 
function checkIfUserExists(userId) {
  var usersRef = new Firebase(USERS_LOCATION);
  usersRef.child(userId).once('value', function(snapshot) {
    var exists = (snapshot.val() !== null);
    userExistsCallback(userId, exists);
  });
}

Firebase userRef= new Firebase(USERS_LOCATION);
userRef.child(userId).addListenerForSingleValueEvent(new ValueEventListener() {
@OverRide
public void onDataChange(DataSnapshot snapshot) {
if (snapshot.getValue() !== null) {
//user exists, do something
} else {
//user does not exist, do something else
}
}
@OverRide
public void onCancelled(FirebaseError arg0) {
}
});

Single user this is ok, but how to compare the more than one user?

I try below type thats not working can u anyone give me a idea for this
Firebase ref= new Firebase(USERS_LOCATION);
ref.addValueEventListener(new ValueEventListener() {
public void onDataChange(DataSnapshot snapshot) {
if (snapshot.getValue() !== null) {
//user exists, do something
} else {
//user does not exist, do something else
}
}
@OverRide
public void onCancelled(FirebaseError arg0) {
}
});

above one is working for username or email or phone only check to find the user already exit or not, but how to i compare the more than one user at a same time to find the user exit or not. i used this
Firebase ref= new Firebase(USERS_LOCATION);
ref.addValueEventListener(new ValueEventListener() {
public void onDataChange(DataSnapshot snapshot) {
if (snapshot.getValue() !== null) {
//user exists, do something
} else {
//user does not exist, do something else
}
}
@OverRide
public void onCancelled(FirebaseError arg0) {
}
});
way but its always going to already exit method only, anyone can explain. how to do that?

That is very strange, when I try to do that in my own application , it does not even go into the function only if data exists which I am tearing hair out because of it.

Awesome. Thanks a lot!

This is awful.

This is definitely an anti-pattern described in the firebase docs.

how to check for more then one value lets say Name: John Surname:Smith how do I check if both exist must i use a two methods?

you probably don't need this but I figured I'd share it. Just feels a bit cleaner to me:

// The ideantifier in the collection.
var uid = 2;
// the data for the object being created/updated.
var user = {
    name: "Luis",
    twitter: "@luisgo"
};
// attempt to get the child in the collection by uid.
db.child('users').child(uid).once('value', function(snapshot){
    // if data exists
    if (snapshot.exists()) {
        // get the ref (in this case /users/2) and update its contents
        snapshot.ref().update(user);
    } else {
        // data does not exist so we wrap the data in an object with
        // a member named after the uid so we can pass it as an update
        // to the parent.
        var payload = {};
            payload[uid] = user;
        // get the ref's parent and call update on it.
        snapshot.ref().parent().update(payload);
    }
});

@lgomez that is brilliant! You saved me so much time.

+1

Can anyone has an idea on how to do it in Laravel?

nice

I am making chat application using java, "https://github.com/Abdul007Malik/Conversa.git", I am confused and cannot progress further help me if you can, my questions:

1. if I know the auth.getUID of others can i modify there data or firebase have different mechanism to check authentication.
2. how can I send the invitation(inviting to join the group) to friends if i know there phone numbers but dont know there particular userid.

This was just perfect. Thank you!

A promise based version (where db is a Firebase ref)

export function checkIfUserExists(authData) {
  return db
    .child('users')
    .child(authData.uid)
    .once('value')
    .then(dataSnapshot => {
      return Promise.resolve({
        authData,
        userExists: dataSnapshot.exists(),
      });
    });
}

Which would be called like so:

  db.authWithOAuthPopup(provider)
    .then(checkIfUserExists)
    .then(({authData, userExists}) => {
      if (userExists) {
        // update user
      } else {
        // go create a user
      }
    })
    .catch(err => {
      console.warn('Error signing in.', err);
    });

Gist: https://gist.github.com/davidgilbertson/52a72f7c5e35502127e5848a8bf881b2

Thanks a lot sir. Helped me construct my own idea

has anyone figured this out using Python? I'm using the following library: https://pypi.python.org/pypi/python-firebase/1.2

Please any body can tell me that i have request record in firebase . i want to get spesific user which userId is 91 how i can access this user by query on firebase

{
"request" :
{
"123" :
{
"userId" : "90",
"name" : "mary"
},
"124" :
{
"userId" : "91",
"name" : "johan"
},
"124" :
{
"userId" : "92",
"name" : "maikal"
}
}
}

How to retrieve the user email using the user id (client id)?

sudikrt, create a table with names and emails and add data to it after user has registered. then you will be able to search for records by email or id.

The crux: var exists = (snapshot.val() !== null);

if you want to listen on a node. You can change the implementation to the snippet below.

  const checkIfUserExists = (userId) => {
    const usersRef = new Firebase(USERS_LOCATION);
    usersRef.child(userId).on('value', (snap) => {
    const exists = (snap.val() !== null);
    userExistsCallback(userId, exists);
   });
 }

didn't know about the once() method. thanks 👍

Can you do this in swift?

Nice!

+2

I am making chat application using java, "https://github.com/Abdul007Malik/Conversa.git", I am confused and cannot progress further help me if you can, my questions:

1. if I know the auth.getUID of others can i modify there data or firebase have different mechanism to check authentication.
2. how can I send the invitation(inviting to join the group) to friends if i know there phone numbers but dont know there particular userid.

Did you find any solution for this. I am facing same issue where I know email id but not user id

Can you give us python examples??

Can you give us python examples??

For python example
https://stackoverflow.com/questions/59253867/how-to-check-if-a-child-in-firebase-database-exists-using-django/60844998#60844998

thank's man, very helpful =)