Added test, CHANGELOG

Author: Anton-Shutik

CHANGELOG.md

@@ -20,6 +20,7 @@ any parts of the framework not mentioned in the documentation should generally b
 * Don't swallow `filter[]` params when there are several
 * Fix DeprecationWarning regarding collections.abc import in Python 3.7
 * Allow OPTIONS request to be used on RelationshipView.
+* Use DRF code when extracting relation instance. [PR](https://github.com/django-json-api/django-rest-framework-json-api/pull/632)
 
 ## [2.7.0] - 2019-01-14
 

example/tests/test_renderers.py

@@ -0,0 +1,49 @@
+from django.test import TestCase
+
+from example.models import Blog, Entry, Comment
+from example.serializers import EntrySerializer
+from rest_framework_json_api import serializers
+from rest_framework_json_api.renderers import JSONRenderer
+
+
+class TestJSONRenderer(TestCase):
+
+    def setUp(self):
+        pass
+
+    def test_extract_relation_instance(self):
+
+        class NewEntySerializer(EntrySerializer):
+            blog_name = serializers.ReadOnlyField(source='blog.name')
+
+            class Meta(EntrySerializer.Meta):
+                fields = EntrySerializer.Meta.fields + ('blog_name',)
+
+        blog = Blog.objects.create(name='Some Blog', tagline="It's a blog")
+        entry = Entry.objects.create(
+            blog=blog,
+            headline='headline',
+            body_text='body_text',
+        )
+        suggested_enty = Entry.objects.create(
+            blog=blog,
+            headline='suggested headline',
+            body_text='suggested body_text',
+        )
+        comment = Comment.objects.create(entry=entry, body='foo')
+        serializer = NewEntySerializer(instance=entry)
+
+        got = JSONRenderer.extract_relation_instance(
+            field=serializer.fields['featured'], resource_instance=entry
+        )
+        assert got == suggested_enty
+
+        got = JSONRenderer.extract_relation_instance(
+            field=serializer.fields['comments'], resource_instance=entry
+        )
+        assert str(got.query) == str(Comment.objects.filter(entry=entry).query)
+
+        got = JSONRenderer.extract_relation_instance(
+            field=serializer.fields['blog_name'], resource_instance=entry
+        )
+        assert got == blog.name

rest_framework_json_api/renderers.py

@@ -299,7 +299,7 @@ def extract_relationships(cls, fields, resource, resource_instance):
         return utils._format_object(data)
 
     @classmethod
-    def extract_relation_instance(cls, field_name, field, resource_instance, serializer):
+    def extract_relation_instance(cls, field, resource_instance):
         """
         Determines what instance represents given relation and extracts it.
 
@@ -351,7 +351,7 @@ def extract_included(cls, fields, resource, resource_instance, included_resource
                     continue
 
             relation_instance = cls.extract_relation_instance(
-                field_name, field, resource_instance, current_serializer
+                field, resource_instance
             )
             if isinstance(relation_instance, Manager):
                 relation_instance = relation_instance.all()