title: Firebase: action after read child
body: <p>I'm working on project that sell <strong>unique</strong> soft products like serials or tickets. To be fast and reliable, we going to use <strong>Firebase Real-time Database</strong>.<br>
  The problem is I want to remove or update the sold ticket after the user get it. </p>
  
  <p>One way to do so is using another server to do so manage the tickets and update the <strong>Firebase</strong> Database using <strong>REST API</strong>, but I want to do it with the <strong>Firebase</strong> only. </p>
  
  <p>Another way to do it, after the user get a ticket, the client side app will sent a remove request. But I'm afraid of losing the data in the middle of this process. A user got a ticket but never removed from the database. As I said the ticket is <strong>unique</strong>. </p>
  
  <p>How to do it with <strong>Firebase</strong> side only?</p>