Firebase Android - Check if value is already exists

Question

I need help regarding checking if the value is already exists in the database so Users won't be able to change it to the same number when they're updating it, like a unique ID

I've been searching for hours for a solution but I can't find any that's working.

Answer 1

To achieve this, I recommend you create another node named userIds . Every time a new user is created just add the user id in this new section. This new section should look like this:

Firebase-root
    --- userIds
      --- Id101: true
      --- Id102: true

Then just put a listener on this new node node and use exists() method on the dataSnapshot object.

Answer 2

As recommended before you should have a data structure, an index list, for this, why? Because when you have tons of this ids it will be a better query. However, I think what you are trying to do is complementary to the previous suggestions.

What you have to do is use a single event listener, if the datasnapshot is not null, then the value exists. The key is query the id you need:

DatabaseReference root = FirebaseDatabase.getInstance.getReference();
DatabaseReference reference = root.child("Test").oderByChild("ID").equalsTo(someId);

reference.addSingleValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
       if (dataSnaphot != null) {
       //This means the value exist, you could also dataSnaphot.exist()
       }
    }
    //More auto generated code
);

The dataSnapshot is a bunch of your objects, because the query could match more than one result. You can iterate inside of it if you need the value of each:

public void onDataChange(DataSnapshot dataSnapshot) {
           if (dataSnaphot != null) {
           for (DataSnapshot children : dataSnaphot.getChildrens()) {
               YourModel yourModel = children.getValue(YourModel.class);
           }
           }
        }