title: Django - Access fields on a model's "through" table from an instance
body: <p>I have a many-to-many relationship with a through table like so:</p>
  
  <pre><code>class Chapter(models.Model):
      name = models.CharField(max_length=255,)
      slides = models.ManyToManyField('Slide', blank=True, related_name='chapters', through='SlideOrder')
      # ...
  
  class Slide(models.Model):
      title = models.CharField(max_length=255,)
      # ...
  
  class SlideOrder(models.Model):
      chapter = models.ForeignKey(Chapter)
      slide = models.ForeignKey(Slide)
      number = models.PositiveIntegerField()
  </code></pre>
  
  <p>I am able to get the slides for a chapter in order like so:</p>
  
  <pre><code>chapter = Chapter.objects.get(pk=1)
  chapter_slides = chapter.slides.order_by('slideorder')
  </code></pre>
  
  <p>However, when working on an individual slide instance I am unable to access the slide order:</p>
  
  <pre><code>slide = Slide.objects.get(pk=1)
  </code></pre>
  
  <p>If I do the following on my slide instance I can see all possible fields:</p>
  
  <pre><code>print slide._meta.get_all_field_names()
  ['title', u'chapters', 'slideorder', u'id']
  </code></pre>
  
  <p>However trying to access the <code>slideorder</code> field gives me the following:</p>
  
  <pre><code>slide.slideorder
  Traceback (most recent call last):
    File "&lt;console&gt;", line 1, in &lt;module&gt;
  AttributeError: 'Slide' object has no attribute 'slideorder'
  </code></pre>
  
  <p>I am able to access all attributes listed except <code>slideorder</code>.  How can I access a slide's order?</p>