title: Replace list comprehension with FK lookup
body: <p>I currently have the following list comprehension:</p>
  
  <pre><code>[item.service.name for item in OrderItem.objects.all()]
  </code></pre>
  
  <p><code>service</code> is a FK on <code>OrderItem</code>, so the above code is doing tons and tons of useless FK lookups. How would I get all <code>services</code> in a single query?</p>