add support for GenericRelation field

django_readers/qs.py

@@ -1,3 +1,4 @@
+from django.contrib.contenttypes.fields import ReverseGenericManyToOneDescriptor
 from django.db.models import Prefetch, QuerySet
 from django.db.models.constants import LOOKUP_SEP
 from django.db.models.fields.related_descriptors import (
@@ -167,6 +168,32 @@ def prefetch_reverse_relationship(
     )
 
 
+def prefetch_reverse_generic_relationship(
+    name, related_field, related_queryset, prepare_related_queryset=noop, to_attr=None
+):
+    """
+    Efficiently prefetch a reverse generic relationship: one where the field on the "parent"
+    queryset is a `GenericRelation` field. We need to include this field in the query.
+    """
+    return pipe(
+        include_fields(name),
+        prefetch_related(
+            Prefetch(
+                name,
+                pipe(
+                    include_fields(
+                        "pk",
+                        related_field.content_type_field_name,
+                        related_field.object_id_field_name,
+                    ),
+                    prepare_related_queryset,
+                )(related_queryset),
+                to_attr,
+            )
+        ),
+    )
+
+
 def prefetch_many_to_many_relationship(
     name, related_queryset, prepare_related_queryset=noop, to_attr=None
 ):
@@ -246,5 +273,13 @@ def prepare(queryset):
                 prepare_related_queryset,
                 to_attr,
             )(queryset)
+        if type(related_descriptor) is ReverseGenericManyToOneDescriptor:
+            return prefetch_reverse_generic_relationship(
+                name,
+                related_descriptor.rel.field,
+                related_descriptor.field.related_model.objects.all(),
+                prepare_related_queryset,
+                to_attr,
+            )(queryset)
 
     return prepare

tests/models.py

@@ -1,6 +1,17 @@
+from django.contrib.contenttypes.fields import GenericRelation
 from django.db import models
 
 
+class LogEntry(models.Model):
+    content_type = models.ForeignKey(
+        to="contenttypes.ContentType",
+        on_delete=models.CASCADE,
+        related_name="+",
+    )
+    object_pk = models.CharField(max_length=255)
+    event = models.CharField(max_length=100)
+
+
 class Group(models.Model):
     name = models.CharField(max_length=100)
 
@@ -15,6 +26,9 @@ class Widget(models.Model):
     value = models.PositiveIntegerField(default=0)
     other = models.CharField(max_length=100, null=True)
     owner = models.ForeignKey(Owner, null=True, on_delete=models.SET_NULL)
+    logs = GenericRelation(
+        LogEntry, content_type_field="content_type", object_id_field="object_pk"
+    )
 
 
 class Thing(models.Model):

tests/test_rest_framework.py

@@ -1,3 +1,4 @@
+from django.contrib.contenttypes.models import ContentType
 from django.core.exceptions import ImproperlyConfigured
 from django.test import TestCase
 from django_readers import pairs, qs
@@ -10,7 +11,7 @@
 from rest_framework import serializers
 from rest_framework.generics import ListAPIView, RetrieveAPIView
 from rest_framework.test import APIRequestFactory
-from tests.models import Category, Group, Owner, Widget
+from tests.models import Category, Group, LogEntry, Owner, Widget
 from textwrap import dedent
 
 
@@ -28,6 +29,7 @@ class WidgetListView(SpecMixin, ListAPIView):
                 },
             ]
         },
+        {"logs": ["event"]},
     ]
 
 
@@ -53,17 +55,32 @@ class CategoryDetailView(SpecMixin, RetrieveAPIView):
 
 class RESTFrameworkTestCase(TestCase):
     def test_list(self):
-        Widget.objects.create(
+        widget = Widget.objects.create(
             name="test widget",
             owner=Owner.objects.create(
                 name="test owner", group=Group.objects.create(name="test group")
             ),
         )
+        LogEntry.objects.create(
+            content_type=ContentType.objects.get_for_model(widget),
+            object_pk=widget.id,
+            event="CREATED",
+        )
+        LogEntry.objects.create(
+            content_type=ContentType.objects.get_for_model(widget),
+            object_pk=widget.id,
+            event="UPDATED",
+        )
+        LogEntry.objects.create(
+            content_type=ContentType.objects.get_for_model(widget),
+            object_pk=widget.id,
+            event="DELETED",
+        )
 
         request = APIRequestFactory().get("/")
         view = WidgetListView.as_view()
 
-        with self.assertNumQueries(3):
+        with self.assertNumQueries(4):
             response = view(request)
 
         self.assertEqual(
@@ -77,6 +94,11 @@ def test_list(self):
                             "name": "test group",
                         },
                     },
+                    "logs": [
+                        {"event": "CREATED"},
+                        {"event": "UPDATED"},
+                        {"event": "DELETED"},
+                    ],
                 }
             ],
         )