Use PreloadIncludesMixin for ReadOnlyModelViewSet (#946)

Author: anehx

AUTHORS

@@ -14,6 +14,7 @@ Jamie Bliss <[email protected]>
 Jason Housley <[email protected]>
 Jeppe Fihl-Pearson <[email protected]>
 Jerel Unruh <[email protected]>
+Jonas Metzener <[email protected]>
 Jonathan Senecal <[email protected]>
 Joseba Mendivil <[email protected]>
 Kevin Partington <[email protected]>

CHANGELOG.md

@@ -8,6 +8,12 @@ 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
+
+* Include `PreloadIncludesMixin` in `ReadOnlyModelViewSet` to enable the usage of [performance utilities](https://django-rest-framework-json-api.readthedocs.io/en/stable/usage.html#performance-improvements) on read only views (regression since 2.8.0)
+
 ## [4.2.0] - 2021-05-12
 
 ### Added

docs/usage.md

@@ -942,7 +942,7 @@ class QuestSerializer(serializers.ModelSerializer):
 
 Be aware that using included resources without any form of prefetching **WILL HURT PERFORMANCE** as it will introduce m\*(n+1) queries.
 
-A viewset helper was therefore designed to automatically preload data when possible. Such is automatically available when subclassing `ModelViewSet`.
+A viewset helper was therefore designed to automatically preload data when possible. Such is automatically available when subclassing `ModelViewSet` or `ReadOnlyModelViewSet`.
 
 It also allows to define custom `select_related` and `prefetch_related` for each requested `include` when needed in special cases:
 

example/migrations/0009_labresults_author.py

@@ -0,0 +1,25 @@
+# Generated by Django 3.2.3 on 2021-05-26 03:32
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("example", "0008_labresults"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="labresults",
+            name="author",
+            field=models.ForeignKey(
+                blank=True,
+                null=True,
+                on_delete=django.db.models.deletion.CASCADE,
+                related_name="lab_results",
+                to="example.author",
+            ),
+        ),
+    ]

example/models.py

@@ -161,6 +161,13 @@ class LabResults(models.Model):
     )
     date = models.DateField()
     measurements = models.TextField()
+    author = models.ForeignKey(
+        Author,
+        null=True,
+        blank=True,
+        on_delete=models.CASCADE,
+        related_name="lab_results",
+    )
 
 
 class Company(models.Model):

example/serializers.py

@@ -356,9 +356,11 @@ class Meta:
 
 
 class LabResultsSerializer(serializers.ModelSerializer):
+    included_serializers = {"author": AuthorSerializer}
+
     class Meta:
         model = LabResults
-        fields = ("date", "measurements")
+        fields = ("date", "measurements", "author")
 
 
 class ProjectSerializer(serializers.PolymorphicModelSerializer):

example/tests/test_performance.py

@@ -1,8 +1,11 @@
+from datetime import date, timedelta
+from random import randint
+
 from django.utils import timezone
 from rest_framework.test import APITestCase
 
 from example.factories import CommentFactory, EntryFactory
-from example.models import Author, Blog, Comment, Entry
+from example.models import Author, Blog, Comment, Entry, LabResults, ResearchProject
 
 
 class PerformanceTestCase(APITestCase):
@@ -84,3 +87,32 @@ def test_query_prefetch_uses_included_resources(self):
                 "/entries?fields[entries]=comments&page[size]=25"
             )
             self.assertEqual(len(response.data["results"]), 25)
+
+    def test_query_prefetch_read_only(self):
+        """We expect a read only list view with an include have five queries:
+
+        1. Primary resource COUNT query
+        2. Primary resource SELECT
+        3. Authors prefetched
+        4. Author types prefetched
+        5. Entries prefetched
+        """
+        project = ResearchProject.objects.create(
+            topic="Mars Mission", supervisor="Elon Musk"
+        )
+
+        LabResults.objects.bulk_create(
+            [
+                LabResults(
+                    research_project=project,
+                    date=date.today() + timedelta(days=i),
+                    measurements=randint(0, 10000),
+                    author=self.author,
+                )
+                for i in range(20)
+            ]
+        )
+
+        with self.assertNumQueries(5):
+            response = self.client.get("/lab-results?include=author&page[size]=25")
+            self.assertEqual(len(response.data["results"]), 20)

example/urls.py

@@ -17,6 +17,7 @@
     CompanyViewset,
     EntryRelationshipView,
     EntryViewSet,
+    LabResultViewSet,
     NonPaginatedEntryViewSet,
     ProjectTypeViewset,
     ProjectViewset,
@@ -32,6 +33,7 @@
 router.register(r"companies", CompanyViewset)
 router.register(r"projects", ProjectViewset)
 router.register(r"project-types", ProjectTypeViewset)
+router.register(r"lab-results", LabResultViewSet)
 
 urlpatterns = [
     url(r"^", include(router.urls)),

example/urls_test.py

@@ -15,6 +15,7 @@
     EntryRelationshipView,
     EntryViewSet,
     FiltersetEntryViewSet,
+    LabResultViewSet,
     NoFiltersetEntryViewSet,
     NonPaginatedEntryViewSet,
     ProjectTypeViewset,
@@ -36,6 +37,7 @@
 router.register(r"companies", CompanyViewset)
 router.register(r"projects", ProjectViewset)
 router.register(r"project-types", ProjectTypeViewset)
+router.register(r"lab-results", LabResultViewSet)
 
 # for the old tests
 router.register(r"identities", Identity)

example/views.py

@@ -14,9 +14,22 @@
 )
 from rest_framework_json_api.pagination import JsonApiPageNumberPagination
 from rest_framework_json_api.utils import format_drf_errors
-from rest_framework_json_api.views import ModelViewSet, RelationshipView
+from rest_framework_json_api.views import (
+    ModelViewSet,
+    ReadOnlyModelViewSet,
+    RelationshipView,
+)
 
-from example.models import Author, Blog, Comment, Company, Entry, Project, ProjectType
+from example.models import (
+    Author,
+    Blog,
+    Comment,
+    Company,
+    Entry,
+    LabResults,
+    Project,
+    ProjectType,
+)
 from example.serializers import (
     AuthorDetailSerializer,
     AuthorListSerializer,
@@ -27,6 +40,7 @@
     CompanySerializer,
     EntryDRFSerializers,
     EntrySerializer,
+    LabResultsSerializer,
     ProjectSerializer,
     ProjectTypeSerializer,
 )
@@ -266,3 +280,12 @@ class CommentRelationshipView(RelationshipView):
 class AuthorRelationshipView(RelationshipView):
     queryset = Author.objects.all()
     self_link_view_name = "author-relationships"
+
+
+class LabResultViewSet(ReadOnlyModelViewSet):
+    queryset = LabResults.objects.all()
+    serializer_class = LabResultsSerializer
+    prefetch_for_includes = {
+        "__all__": [],
+        "author": ["author__bio", "author__entries"],
+    }

rest_framework_json_api/views.py

@@ -224,7 +224,7 @@ class ModelViewSet(
 
 
 class ReadOnlyModelViewSet(
-    AutoPrefetchMixin, RelatedMixin, viewsets.ReadOnlyModelViewSet
+    AutoPrefetchMixin, PreloadIncludesMixin, RelatedMixin, viewsets.ReadOnlyModelViewSet
 ):
     http_method_names = ["get", "post", "patch", "delete", "head", "options"]