title: Retrieving a Foreign Key value with django-rest-framework serializers
body: <p>I'm using the django rest framework to create an API. 
  I have the following models:</p>
  
  <pre><code>class Category(models.Model):
      name = models.CharField(max_length=100)
  
      def __unicode__(self):
          return self.name
  
  
  class Item(models.Model):
      name = models.CharField(max_length=100)
      category = models.ForeignKey(Category, related_name='items')
  
      def __unicode__(self):
          return self.name
  </code></pre>
  
  <p>To create a serializer for the categories I'd do:</p>
  
  <pre><code>class CategorySerializer(serializers.ModelSerializer):
      items = serializers.RelatedField(many=True)
  
      class Meta:
          model = Category
  </code></pre>
  
  <p>... and this would provide me with:</p>
  
  <pre><code>[{'items': [u'Item 1', u'Item 2', u'Item 3'], u'id': 1, 'name': u'Cat 1'},
   {'items': [u'Item 4', u'Item 5', u'Item 6'], u'id': 2, 'name': u'Cat 2'},
   {'items': [u'Item 7', u'Item 8', u'Item 9'], u'id': 3, 'name': u'Cat 3'}]
  </code></pre>
  
  <p>How would I go about getting the reverse from an Item serializer, ie:</p>
  
  <pre><code>[{u'id': 1, 'name': 'Item 1', 'category_name': u'Cat 1'},
  {u'id': 2, 'name': 'Item 2', 'category_name': u'Cat 1'},
  {u'id': 3, 'name': 'Item 3', 'category_name': u'Cat 1'},
  {u'id': 4, 'name': 'Item 4', 'category_name': u'Cat 2'},
  {u'id': 5, 'name': 'Item 5', 'category_name': u'Cat 2'},
  {u'id': 6, 'name': 'Item 6', 'category_name': u'Cat 2'},
  {u'id': 7, 'name': 'Item 7', 'category_name': u'Cat 3'},
  {u'id': 8, 'name': 'Item 8', 'category_name': u'Cat 3'},
  {u'id': 9, 'name': 'Item 9', 'category_name': u'Cat 3'}]
  </code></pre>
  
  <p>I've read through the docs on <a href="https://www.django-rest-framework.org/api-guide/relations/#reverse-relations" rel="noreferrer">reverse relationships</a> for the rest framework but that appears to be the same result as the non-reverse fields.  Am I missing something obvious?</p>