title: Get all ids from a collection
body: <p>I got my collection items like this : </p>
  
  <pre><code>hotels = Hotel.where('selection = ?', 1).limit(4)
  </code></pre>
  
  <p>How can I get all ids of this items without a loop? Can i use something like : </p>
  
  <pre><code>hotels.ids ? 
  </code></pre>
  
  <p>Thank you</p>