title: Get file URL from raw django SQL query
body: <p>I have two models</p>
  <pre><code>class Post(models.Model):
     ...
  
  class PostImage(models.Model):
     post = models.ForeignKey(Post)
     ...
  </code></pre>
  <p>In a ListView I need to query a post and one image for it, so I end up writing a raw query.
  What I hit now is that the url fields are simple path strings which Django tries to
  load from my app, instead of the MEDIA_URL which otherwise works if the object is loaded via the ORM.</p>
  <p>Is there a way to convert that path to the URL in the template using the Django syntax ?</p>
  <pre><code>{{ post.image.url }}
  </code></pre>