Query nested data from Firebase Real-time database Android

Question

I have the structure in the image below and I want to get the whole data from the node \"aaa1234\" querying by \"id_Usuario\". How can I do that query?

Answer 1

I see two mistakes.

The first one is a typo, which I already marked in my comment. You're storing the user ID as a number, so shouldn't have quotes around the value in equalTo. So: .equalTo(2)

The second mistake is in the way you try to query:

DatabaseReference root = database.getReference().child("Eventos").child("participantes");

This will create a reference to the non-existing child Eventos/participantes. What you want to do instead is query Eventos, but then against property participantes/id_Usuario. So

DatabaseReference root = database.getReference().child("Eventos");
Query query = root.orderByChild("participantes/id_Usuario").equalTo(2);