Avoid exception when trying to include skipped relationship

AUTHORS

@@ -22,3 +22,4 @@ Yaniv Peer <[email protected]>
 Mohammed Ali Zubair <[email protected]>
 Jason Housley <[email protected]>
 Beni Keller <[email protected]>
+Stas S. <[email protected]>

CHANGELOG.md

@@ -8,6 +8,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 Note that in line with [Django REST Framework policy](http://www.django-rest-framework.org/topics/release-notes/),
 any parts of the framework not mentioned in the documentation should generally be considered private API, and may be subject to change.
 
+## [Unreleased]
+
+### Fixed
+
+* Avoid exception when trying to include skipped relationship
 
 ## [2.7.0] - 2019-01-14
 

example/serializers.py

@@ -1,6 +1,6 @@
 from datetime import datetime
 
-from rest_framework import serializers as drf_serilazers
+from rest_framework import serializers as drf_serilazers, fields as drf_fields
 
 from rest_framework_json_api import relations, serializers
 
@@ -318,15 +318,40 @@ class Meta:
         exclude = ('polymorphic_ctype',)
 
 
+class CurrentProjectRelatedField(relations.PolymorphicResourceRelatedField):
+    def get_attribute(self, instance):
+        obj = super(CurrentProjectRelatedField, self).get_attribute(instance)
+
+        is_art = (
+            self.field_name == 'current_art_project' and
+            isinstance(obj, ArtProject)
+        )
+        is_res = (
+            self.field_name == 'current_research_project' and
+            isinstance(obj, ResearchProject)
+        )
+
+        if is_art or is_res:
+            return obj
+
+        raise drf_fields.SkipField()
+
+
 class CompanySerializer(serializers.ModelSerializer):
     current_project = relations.PolymorphicResourceRelatedField(
         ProjectSerializer, queryset=Project.objects.all())
+    current_art_project = CurrentProjectRelatedField(
+        ProjectSerializer, source='current_project', read_only=True)
+    current_research_project = CurrentProjectRelatedField(
+        ProjectSerializer, source='current_project', read_only=True)
     future_projects = relations.PolymorphicResourceRelatedField(
         ProjectSerializer, queryset=Project.objects.all(), many=True)
 
     included_serializers = {
         'current_project': ProjectSerializer,
         'future_projects': ProjectSerializer,
+        'current_art_project': ProjectSerializer,
+        'current_research_project': ProjectSerializer
     }
 
     class Meta:

example/tests/integration/test_polymorphism.py

@@ -25,10 +25,13 @@ def test_polymorphism_on_detail_relations(single_company, client):
 
 
 def test_polymorphism_on_included_relations(single_company, client):
-    response = client.get(reverse("company-detail", kwargs={'pk': single_company.pk}) +
-                          '?include=current_project,future_projects')
+    response = client.get(
+        reverse("company-detail", kwargs={'pk': single_company.pk}) +
+        '?include=current_project,future_projects,current_art_project,current_research_project')
     content = response.json()
     assert content["data"]["relationships"]["currentProject"]["data"]["type"] == "artProjects"
+    assert content["data"]["relationships"]["currentArtProject"]["data"]["type"] == "artProjects"
+    assert content["data"]["relationships"]["currentResearchProject"]["data"] is None
     assert (
         set([rel["type"] for rel in content["data"]["relationships"]["futureProjects"]["data"]]) ==
         set(["researchProjects", "artProjects"])

rest_framework_json_api/renderers.py

@@ -375,7 +375,7 @@ def extract_included(cls, fields, resource, resource_instance, included_resource
                 serializer_data = field.data
 
             if isinstance(field, relations.RelatedField):
-                if relation_instance is None:
+                if relation_instance is None or not serializer_data:
                     continue
 
                 many = field._kwargs.get('child_relation', None) is not None