title: How to sort activerecord query by specific prority
body: <p>I am using rails 3 and postrges.</p>
  
  <p>I would like order by a specific priority.</p>
  
  <p>Something like:</p>
  
  <pre><code>Assignment.order(priority: ['best', 'good', 'bad'])
  </code></pre>
  
  <p>and this will return all activerecords first with 'best', then 'good', then 'bad'</p>
  
  <p>I cannot seem to find anything like this. I do not need an array, it has to be activerecords.</p>