Use REST framework serializer functionality to extract includes (#632)

Author: Anton-Shutik

CHANGELOG.md

@@ -18,6 +18,8 @@ any parts of the framework not mentioned in the documentation should generally b
 
 * Allow to define `select_related` per include using [select_for_includes](https://django-rest-framework-json-api.readthedocs.io/en/stable/usage.html#performance-improvements)
 * Reduce number of queries to calculate includes by using `select_related` when possible
+* Use REST framework serializer functionality to extract includes. This adds support like using
+  dotted notations in source attribute in `ResourceRelatedField`.
 
 ### Fixed
 

example/tests/unit/test_renderers.py

@@ -10,9 +10,11 @@
 
 # serializers
 class RelatedModelSerializer(serializers.ModelSerializer):
+    blog = serializers.ReadOnlyField(source='entry.blog')
+
     class Meta:
         model = Comment
-        fields = ('id',)
+        fields = ('id', 'blog')
 
 
 class DummyTestSerializer(serializers.ModelSerializer):
@@ -137,3 +139,13 @@ class EmptyRelationshipViewSet(views.ReadOnlyModelViewSet):
     assert 'relationships' in result['data']
     assert 'bio' in result['data']['relationships']
     assert result['data']['relationships']['bio'] == {'data': None}
+
+
+@pytest.mark.django_db
+def test_extract_relation_instance(comment):
+    serializer = RelatedModelSerializer(instance=comment)
+
+    got = JSONRenderer.extract_relation_instance(
+        field=serializer.fields['blog'], resource_instance=comment
+    )
+    assert got == comment.entry.blog

rest_framework_json_api/renderers.py

@@ -8,6 +8,8 @@
 from django.db.models import Manager
 from django.utils import encoding, six
 from rest_framework import relations, renderers
+from rest_framework.fields import SkipField, get_attribute
+from rest_framework.relations import PKOnlyObject
 from rest_framework.serializers import BaseSerializer, ListSerializer, Serializer
 from rest_framework.settings import api_settings
 
@@ -297,34 +299,20 @@ 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.
 
-        Relation instance is determined by given field_name or source configured on
-        field. As fallback is a serializer method called with name of field's source.
+        Relation instance is determined exactly same way as it determined
+        in parent serializer
         """
-        relation_instance = None
-
         try:
-            relation_instance = getattr(resource_instance, field_name)
-        except AttributeError:
-            try:
-                # For ManyRelatedFields if `related_name` is not set
-                # we need to access `foo_set` from `source`
-                relation_instance = getattr(resource_instance, field.child_relation.source)
-            except AttributeError:
-                if hasattr(serializer, field.source):
-                    serializer_method = getattr(serializer, field.source)
-                    relation_instance = serializer_method(resource_instance)
-                else:
-                    # case when source is a simple remap on resource_instance
-                    try:
-                        relation_instance = getattr(resource_instance, field.source)
-                    except AttributeError:
-                        pass
-
-        return relation_instance
+            res = field.get_attribute(resource_instance)
+            if isinstance(res, PKOnlyObject):
+                return get_attribute(resource_instance, field.source_attrs)
+            return res
+        except SkipField:
+            return None
 
     @classmethod
     def extract_included(cls, fields, resource, resource_instance, included_resources,
@@ -363,7 +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()