title: How to order a Django Rest Framework ManyToMany related field?
body: <p>I have a Django Rest Framework application with the following (simplified) <code>models.py</code>:</p>
  
  <pre><code>class Photo(models.Model):
      ...
  
  class Album(models.Model):
      ...
      photos = models.ManyToManyField(Photo, through='PhotoInAlbum', related_name='albums')
  
  class PhotoInAlbum(models.Model):
  
      photo = models.ForeignKey(Photo)
      album = models.ForeignKey(Album)
  
      order = models.IntegerField()
  
      class Meta:
          ordering = ['album', 'order']
  </code></pre>
  
  <p>And in my <code>serializers.py</code>, I have the following:</p>
  
  <pre><code>class AlbumSerializer(serializers.ModelSerializer):
  
      ...
      photos = serializers.PrimaryKeyRelatedField('photos', many=True)
  </code></pre>
  
  <p>My question is, how can I have <code>AlbumSerializer</code> return the photos ordered by the field <code>order</code>?</p>