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

users = new HashMap<>();
                users.put("UserID", milisec);
                users.put("UserName", username);
                users.put("UserEmailID", email);
                users.put("UserPhoneNumber", phoneno);
                users.put("UserPassword", hiddenEditPassword);
                users.put("UserDateTime", new Timestamp(new Date()));
                users.put("UserProfileImage", " ");

                FirebaseFirestore.getInstance().collection("Users").document(phoneno).get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
                    @Override
                    public void onComplete(@NonNull Task<DocumentSnapshot> task) {
                        if (task.getResult().exists()) {
                            Toast.makeText(SignupActivity.this, "Already User", Toast.LENGTH_SHORT).show();

                        } else {
                            FirebaseFirestore.getInstance().collection("Users")
                                    .document(phoneno).set(users).addOnCompleteListener(new OnCompleteListener<Void>() {
                                @Override
                                public void onComplete(@NonNull Task<Void> task) {
                                    Toast.makeText(SignupActivity.this, "Registers", Toast.LENGTH_SHORT).show();

                                }
                            });
                        }
                        hideProgressDialog();
                    }
                });`
enter code here

Answer 2

You can check snapshot.exists value.

NSString *roomId = @"room1";
FIRDatabaseReference *refUniqRoom = [[[[FIRDatabase database] reference]
                                      child:@"rooms"]
                                     child:roomId];

[refUniqRoom observeSingleEventOfType:FIRDataEventTypeValue
                            withBlock:^(FIRDataSnapshot * _Nonnull snapshot) {

    bool isExists = snapshot.exists;
    NSLog(@"%d", isExists);
}];

Answer 3

self.ref = FIRDatabase.database().reference()

   ref.child("rooms").observeSingleEvent(of: .value, with: { (snapshot) in

        if snapshot.hasChild("room1"){

            print("true rooms exist")

        }else{

            print("false room doesn't exist")
        }


    })

Answer 4

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.

Answer 5

Use any of them So simple and easy ... Which way you like

ValueEventListener responseListener = new ValueEventListener() {
    @Override    
    public void onDataChange(DataSnapshot dataSnapshot) {
        if (dataSnapshot.exists()) {
            // Do stuff        
        } else {
            // Do stuff        
        }
    }

    @Override    
    public void onCancelled(DatabaseError databaseError) {

    }
};

FirebaseUtil.getResponsesRef().child(postKey).addValueEventListener(responseListener);

---

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) {
    }
});

Answer 6

While the answer of @ismael33 works, it downloads all the rooms to check if room1 exists.

The following code accomplishes the same, but then only downloads rooms/room1 to do so:

ref = FIRDatabase.database().reference()

ref.child("rooms/room1").observeSingleEvent(of: .value, with: { (snapshot) in
    if snapshot.exists(){
        print("true rooms exist")
    }else{
        print("false room doesn't exist")
    }
})