title: RTDB Rules - only updatable before time (time that is referenced in other path)
body: <p>I have two paths:</p>
  <pre><code>/lotteries
  ----/uniqueID001
  -------/active: true
  -------/choicesCutoff
  ---------/1: 11th August 2020 10:41 AM
  ---------/2: 11th August 2020 11:41 AM
  
  
  /tickets
  ----/uniqueID0234
  -------/lottery: uniqueID001
  -------/choices
  ---------/1: 'initial choice'
  ---------/2: 'initial choice'
  </code></pre>
  <p>I need to create a database rule so that people cant change their choice after the cutoff.</p>
  <p>i'm currently using <strong>update</strong> like so <code>ref('/tickets/uniqueID0234}/choices').update({1: 'new choice'})</code>
  and have client side logic for disabling changes after the cutoff. This works fine but if the user changes their device time, they will be able to change their ticket.</p>
  <p>How do I write a rule that references the lottery id and the associated cut off; to disable making updates after the cutoff?</p>
  <p><em>(Each choice has a different cutoff)</em></p>