[WIP] Fix example app (#362)

* Add example-specific requirements

* Document installing additional requirements

* Fix polymorphic serializers without any model instances as data

Author: AstraLuma

docs/getting-started.md

@@ -69,7 +69,9 @@ From Source
 ## Running the example app
 
     git clone https://github.com/django-json-api/django-rest-framework-json-api.git
-    cd django-rest-framework-json-api && pip install -e .
+    cd django-rest-framework-json-api
+    pip install -e .
+    pip install -r example/requirements.txt
     django-admin.py runserver
 
 Browse to http://localhost:8000

example/requirements.txt

@@ -0,0 +1,2 @@
+# Requirements specifically for the example app
+packaging

example/tests/integration/test_polymorphism.py

@@ -78,6 +78,30 @@ def test_polymorphism_on_polymorphic_model_list_post(client):
     assert content['data']['attributes']['artist'] == test_artist
 
 
+def test_polymorphic_model_without_any_instance(client):
+    expected = {
+        "links": {
+            "first": "http://testserver/projects?page=1",
+            "last": "http://testserver/projects?page=1",
+            "next": None,
+            "prev": None
+        },
+        "data": [],
+        "meta": {
+            "pagination": {
+                "page": 1,
+                "pages": 1,
+                "count": 0
+            }
+        }
+    }
+
+    response = client.get(reverse('project-list'))
+    assert response.status_code == 200
+    content = load_json(response.content)
+    assert expected == content
+
+
 def test_invalid_type_on_polymorphic_model(client):
     test_topic = 'New test topic {}'.format(random.randint(0, 999999))
     test_artist = 'test-{}'.format(random.randint(0, 999999))

rest_framework_json_api/serializers.py

@@ -219,7 +219,7 @@ def get_fields(self):
         """
         Return an exhaustive list of the polymorphic serializer fields.
         """
-        if self.instance is not None:
+        if self.instance not in (None, []):
             if not isinstance(self.instance, QuerySet):
                 serializer_class = self.get_polymorphic_serializer_for_instance(self.instance)
                 return serializer_class(self.instance, context=self.context).get_fields()