How do I check if a firebase database value exists?

Question

I\'m using the Realtime Database with Google\'s Firebase, and I\'m trying to check if a child exists.

My database is structured as the following

- /          


        

Answer 1

I have some suggestions by using firebase.You check it from firebase.

We can test for the existence of certain keys within a DataSnapshot using its exists() method:

A DataSnapshot contains data from a Firebase database location. Any time you read data from a Firebase database, you receive the data as a DataSnapshot.

A DataSnapshot is passed to the event callbacks you attach with on() or once(). You can extract the contents of the snapshot as a JavaScript object by calling its val() method. Alternatively, you can traverse into the snapshot by calling child() to return child snapshots (which you could then call val() on).

A DataSnapshot is an efficiently-generated, immutable copy of the data at a database location. They cannot be modified and will never change. To modify data, you always use a Firebase reference directly.

exists() - Returns true if this DataSnapshot contains any data. It is slightly more efficient than using snapshot.val() !== null.

Example from firebase documentation(javascript example)

var ref = new Firebase("https://docs-examples.firebaseio.com/samplechat/users/fred");
ref.once("value", function(snapshot) {
  var a = snapshot.exists();
  // a === true

  var b = snapshot.child("rooms").exists();
  // b === true

  var c = snapshot.child("rooms/room1").exists();
  // c === true

  var d = snapshot.child("rooms/room0").exists();
  // d === false (because there is no "rooms/room0" child in the data snapshot)
}); 

Also please refer this page(already mentioned in my comment)

Here there is an example using java.

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) {
    }
});

I hope you got an idea now.