title: How to validate the date input in the form for cakephp?
body: <p>I want to limit the dates that are allowed to be picked by the user if that date already exists for any other lesson. </p>
  
  <pre><code>$validator
              -&gt;date('lesson_date')
              -&gt;requirePresence('lesson_date', 'create')
              -&gt;notEmpty('lesson_date');
  </code></pre>
  
  <p>this is the validator in the Model/Table/LessonsTable.php right now. But i want to be able to check the lesson table and see if any other lesson has the same date. if there isnt, then that date can be chosen, otherwise prompted to choose on the same day next subsequent weeks </p>