title: set a key with push so data don't get overridden
body: <p>I have an issue working with Firebase, I need to have a child called Participants, and a button to add a son that basically is (key= userId, value= username) I already have something like that but the setValue overrides the existed value, I can use push, but with that my key is random, how can I solve that problem?
  Here is my code:</p>
  
  <pre><code>   myRef.child("Participants").child(id).setValue(username);
              participantAdapter.notifyDataSetChanged();
  </code></pre>
  
  <p>Thank you</p>