title: Sails.js expireAfterSeconds option in the model
body: <p>I am using sails to write a simple model which should expire after a few hours, so I need something like </p>
  
  <pre><code>    createdAt: {
          type: 'Date',
          expires : 60,
          index: true
      }
  </code></pre>
  
  <p>But the "expireAfterSeconds" seems not working when I check my database (MongoDB), therefore I have to use</p>
  
  <pre><code>db.collection.ensureIndex( { "createdAt": 1 }, { expireAfterSeconds: 3600 } )
  </code></pre>
  
  <p>I wonder if it is possible to set the "expire" option in the model?</p>