class Post(models.Model):
    text = models.CharField(max_length=256)
    type = models.ForeignKey(PostType)

class PostSerializer(serializers.HyperlinkedModelSerializer):
    type = serializers.SlugRelatedField(queryset=PostType.objects.all(), slug_field='id', allow_null=True, required=False)

class PostTests(APITestCase):
    def test_create(self):
        response = self.client.post('/api/post/', {'text': 'Hello world !'})

# Expected
200

# Actual behavior
  File "/usr/local/lib/python3.5/site-packages/rest_framework/serializers.py", line 509, in data
    ret = super(Serializer, self).data
  File "/usr/local/lib/python3.5/site-packages/rest_framework/serializers.py", line 241, in data
    self._data = self.to_representation(self.validated_data)
  File "/usr/local/lib/python3.5/site-packages/rest_framework/serializers.py", line 469, in to_representation
    attribute = field.get_attribute(instance)
  File "/usr/local/lib/python3.5/site-packages/rest_framework/relations.py", line 165, in get_attribute
    return get_attribute(instance, self.source_attrs)
  File "/usr/local/lib/python3.5/site-packages/rest_framework/fields.py", line 79, in get_attribute
    instance = instance[attr]
KeyError: 'type'