Do not lazy load forward relations

If the forward relations are included, the renderer will break, so this optimization only works if it is not included.

fixup! Do not lazy load forward relations

fixup! Do not lazy load forward relations

fixup! Do not lazy load forward relations

fixup! Do not lazy load forward relations

fixup! Do not lazy load forward relations

Include test case

Small refactoring

Make compatible with Python 2.X

fixup! Make compatible with Python 2.X

Fix travis

Use isort

Implement suggested changes

Make import backward compatible

Make travis happy

Author: Tim Csitkovics

AUTHORS

@@ -15,4 +15,5 @@ Oliver Sauder <os@esite.ch>
 Raphael Cohen <raphael.cohen.utt@gmail.com>
 Roberto Barreda <roberto.barreda@gmail.com>
 santiavenda <santiavenda2@gmail.com>
+Tim Selman <timcbaoth@gmail.com>
 Yaniv Peer <yanivpeer@gmail.com>

CHANGELOG.md

@@ -7,6 +7,8 @@
 * Add optional [jsonapi-style](http://jsonapi.org/format/) sort filter backend. See [usage docs](docs/usage.md#filter-backends)
 * For naming consistency, renamed new `JsonApi`-prefix pagination classes to `JSONAPI`-prefix.
   * Deprecates `JsonApiPageNumberPagination` and `JsonApiLimitOffsetPagination`
+* Fix for performance improvement for related `ModelSerializer`
+
 
 v2.5.0 - Released July 11, 2018
 

example/tests/test_serializers.py

@@ -2,24 +2,39 @@
 from django.test import TestCase
 from django.urls import reverse
 from django.utils import timezone
-
-from rest_framework_json_api.serializers import ResourceIdentifierObjectSerializer
+from rest_framework.request import Request
+from rest_framework.test import APIRequestFactory
+
+from rest_framework_json_api.serializers import (
+    DateField,
+    ModelSerializer,
+    ResourceIdentifierObjectSerializer
+)
 from rest_framework_json_api.utils import format_resource_type
 
 from example.models import Author, Blog, Entry
+from example.serializers import BlogSerializer
+
+try:
+    from unittest import mock
+except ImportError:
+    import mock
 
+request_factory = APIRequestFactory()
 pytestmark = pytest.mark.django_db
 
 
 class TestResourceIdentifierObjectSerializer(TestCase):
     def setUp(self):
         self.blog = Blog.objects.create(name='Some Blog', tagline="It's a blog")
+        now = timezone.now()
+
         self.entry = Entry.objects.create(
             blog=self.blog,
             headline='headline',
             body_text='body_text',
-            pub_date=timezone.now(),
-            mod_date=timezone.now(),
+            pub_date=now.date(),
+            mod_date=now.date(),
             n_comments=0,
             n_pingbacks=0,
             rating=3
@@ -30,6 +45,59 @@ def setUp(self):
                 Author.objects.create(name=name, email='{}@example.org'.format(name))
             )
 
+    def test_forward_relationship_not_loaded_when_not_included(self):
+        to_representation_method = 'example.serializers.BlogSerializer.to_representation'
+        with mock.patch(to_representation_method) as mocked_serializer:
+            class EntrySerializer(ModelSerializer):
+                blog = BlogSerializer()
+
+                class Meta:
+                    model = Entry
+                    fields = '__all__'
+
+            request_without_includes = Request(request_factory.get('/'))
+            serializer = EntrySerializer(context={'request': request_without_includes})
+            serializer.to_representation(self.entry)
+
+            mocked_serializer.assert_not_called()
+
+    def test_forward_relationship_optimization_correct_representation(self):
+        class EntrySerializer(ModelSerializer):
+            blog = BlogSerializer()
+
+            class Meta:
+                model = Entry
+                fields = '__all__'
+
+        request_without_includes = Request(request_factory.get('/'))
+        serializer = EntrySerializer(context={'request': request_without_includes})
+        result = serializer.to_representation(self.entry)
+
+        # Remove non deterministic fields
+        result.pop('created_at')
+        result.pop('modified_at')
+
+        expected = dict(
+            [
+                ('id', 1),
+                ('blog', dict([('type', 'blogs'), ('id', 1)])),
+                ('headline', 'headline'),
+                ('body_text', 'body_text'),
+                ('pub_date', DateField().to_representation(self.entry.pub_date)),
+                ('mod_date', DateField().to_representation(self.entry.mod_date)),
+                ('n_comments', 0),
+                ('n_pingbacks', 0),
+                ('rating', 3),
+                ('authors',
+                    [
+                        dict([('type', 'authors'), ('id', '1')]),
+                        dict([('type', 'authors'), ('id', '2')]),
+                        dict([('type', 'authors'), ('id', '3')]),
+                        dict([('type', 'authors'), ('id', '4')]),
+                        dict([('type', 'authors'), ('id', '5')])])])
+
+        self.assertDictEqual(expected, result)
+
     def test_data_in_correct_format_when_instantiated_with_blog_object(self):
         serializer = ResourceIdentifierObjectSerializer(instance=self.blog)
 

rest_framework_json_api/serializers.py

@@ -182,35 +182,41 @@ def to_representation(self, instance):
 
         for field in readable_fields:
             try:
-
-                if isinstance(field, ModelSerializer) and hasattr(field, field.source + "_id"):
-                    attribute = getattr(instance, field.source + "_id")
-                    if attribute is None:
-                        ret[field.field_name] = None
-                        continue
-                    resource_type = get_resource_type_from_instance(field)
-                    if resource_type:
-                        ret[field.field_name] = OrderedDict([("type", resource_type),
-                                                             ("id", attribute)])
-                        continue
-
-                attribute = field.get_attribute(instance)
+                field_representation = self._get_field_representation(field, instance)
+                ret[field.field_name] = field_representation
             except SkipField:
                 continue
 
-            # We skip `to_representation` for `None` values so that fields do
-            # not have to explicitly deal with that case.
-            #
-            # For related fields with `use_pk_only_optimization` we need to
-            # resolve the pk value.
-            check_for_none = attribute.pk if isinstance(attribute, PKOnlyObject) else attribute
-            if check_for_none is None:
-                ret[field.field_name] = None
-            else:
-                ret[field.field_name] = field.to_representation(attribute)
-
         return ret
 
+    def _get_field_representation(self, field, instance):
+        request = self.context.get('request')
+        is_included = field.source in get_included_resources(request)
+        if not is_included and \
+                isinstance(field, ModelSerializer) and \
+                hasattr(instance, field.source + '_id'):
+            attribute = getattr(instance, field.source + '_id')
+
+            if attribute is None:
+                return None
+
+            resource_type = get_resource_type_from_serializer(field)
+            if resource_type:
+                return OrderedDict([('type', resource_type), ('id', attribute)])
+
+        attribute = field.get_attribute(instance)
+
+        # We skip `to_representation` for `None` values so that fields do
+        # not have to explicitly deal with that case.
+        #
+        # For related fields with `use_pk_only_optimization` we need to
+        # resolve the pk value.
+        check_for_none = attribute.pk if isinstance(attribute, PKOnlyObject) else attribute
+        if check_for_none is None:
+            return None
+        else:
+            return field.to_representation(attribute)
+
 
 class PolymorphicSerializerMetaclass(SerializerMetaclass):
     """