How to search if a username exist in the given firebase database?

Question

{
 users:
  {
    apple:
     {
       username :  apple
       email    :  apple@xy.com
       uid      :  tyutyutyu
     }
    mango:
     {
       username :  man         


        

Answer 1

You may try this.

                final String userName = unameEditText.getText().toString();
                databaseReference.child("users").orderByChild("username").equalTo(userName).addListenerForSingleValueEvent(
                        new ValueEventListener() {

                            @Override
                            public void onDataChange(DataSnapshot dataSnapshot) {

                                Log.i(Constants.TAG, "dataSnapshot value = " + dataSnapshot.getValue());

                                if (dataSnapshot.exists()) {

                                    // User Exists
                                    // Do your stuff here if user already exists
                                    Toast.makeText(getApplicationContext(), "Username already exists. Please try other username.", Toast.LENGTH_SHORT).show();

                                } else {

                                    // User Not Yet Exists
                                    // Do your stuff here if user not yet exists
                                }
                            }
                            @Override
                            public void onCancelled (DatabaseError databaseError){

                            }
                        }

                );

Answer 2

EDIT: New answer, old one still below.

I would get rid of your method "checkFirebaseForUsername" because it will always return 0, no matter what.

What you need to do is this:

DatabaseReference ref = FirebaseDatabase.getInstance().getReference();
ref.child("users").child("username").addListenerForSingleValueEvent(new ValueEventListener() {
  @Override
  public void onDataChange(DataSnapshot dataSnapshot) {
     if(dataSnapshot.exists()){
      // use "username" already exists
      // Let the user know he needs to pick another username.
    } else {
      // User does not exist. NOW call createUserWithEmailAndPassword
      mAuth.createUserWithPassword(...);
      // Your previous code here.

    }                               
  }

  @Override
  public void onCancelled(DatabaseError databaseError) {

  }
});

Old Answer:

{
 users:
  {
    apple[X]:
     {
       username :  apple[Y]
       email    :  apple@xy.com
       uid      :  tyutyutyu
     }
    mango:
     {
       username :  mango
       email    :  mango@xy.com
       uid      :  erererer
     }
  }
}

If for example, the node apple[X] will always have the same name as the child property "username":apple[Y], then it is as simple as this.

DatabaseReference ref = FirebaseDatabase.getInstance().getReference();
ref.child("users").child("username").addListenerForSingleValueEvent(new ValueEventListener() {
  @Override
  public void onDataChange(DataSnapshot dataSnapshot) {
     if(dataSnapshot.exists()){
      // use "username" already exists
    } else {
      // "username" does not exist yet.
    }                               
  }

  @Override
  public void onCancelled(DatabaseError databaseError) {

  }
});

however, if say, the node apple[X] can have a different value than the property apple[Y], and you want to see if any node exists where the "username" property is the same, then you will need to do a query.

 Query query = FirebaseDatabase.getInstance().getReference().child("users").orderByChild("username").equalTo("usernameToCheckIfExists");
 query.addListenerForSingleValueEvent(new ValueEventListener() {
      @Override
      public void onDataChange(DataSnapshot dataSnapshot) {
        if (dataSnapshot.getChildrenCount() > 0) {
            // 1 or more users exist which have the username property "usernameToCheckIfExists"
         }
       }

      @Override
      public void onCancelled(DatabaseError databaseError) {

      }
  });

Answer 3

You just check if user is already exits or not by below code:

    private DatabaseReference mDatabase;
    // ...
    mDatabase = FirebaseDatabase.getInstance().getReference();

    final String userName = "your_user_name"; // replace with your user name
    mDatabase.child("users").child(userName).addListenerForSingleValueEvent(
        new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                if (dataSnapshot.exists()) {
                   // User Exists
                   // Do your stuff here if user already exits
                 }

            }

            @Override
            public void onCancelled(DatabaseError databaseError) {
                Log.w(TAG, "getUser:onCancelled", databaseError.toException());
            }
        });

You can also see Firebase doc for the same on below link:

Read data once