Add regression tests nested relations

tests/test_project/serializers.py

@@ -17,13 +17,27 @@ def get_related(self, eagle: Eagle) -> dict:
         if "previous_locations" in access:
             related["previous_locations"] = [loc.id for loc in eagle.previous_locations.all()]
 
+        if "previous_locations__climates" in access:
+            related["previous_locations__climates"] = [
+                [climate.id for climate in loc.climates.all()] for loc in eagle.previous_locations.all()
+            ]
+
+        if "previous_locations__climates__locations" in access:
+            related["previous_locations__climates__locations"] = [
+                [[home.id for home in climate.locations.all()] for climate in loc.climates.all()]
+                for loc in eagle.previous_locations.all()
+            ]
+
         if "previous_locations_raw" in access:
             cache = eagle._prefetched_objects_cache
             related["previous_locations_raw"] = [loc.id for loc in cache["previous_locations"]]
 
         if "eaglet" in access:
             related["eaglet"] = eagle.eaglet.id
 
+        if "eaglet__eagle" in access:
+            related["eaglet__eagle"] = eagle.eaglet.eagle.id
+
         if "burrow" in access:
             related["burrow"] = eagle.burrow.depth
 

tests/test_project/views.py

@@ -1,6 +1,6 @@
 import contextlib
 
-from django.db.models import Prefetch
+from django.db.models import Model, Prefetch
 from rest_framework.request import Request
 from rest_framework.response import Response
 from rest_framework.views import APIView
@@ -14,6 +14,13 @@ def _csv(value: str | None) -> list[str]:
     return [item for item in (value or "").split(",") if item]
 
 
+def _resolve_related_model(model: type[Model], lookup: str) -> type[Model]:
+    # Walk a ``__``-separated relation lookup from *model* and return the model at the end.
+    for part in lookup.split("__"):
+        model = model._meta.get_field(part).related_model
+    return model
+
+
 class EagleView(APIView):
     def get(self, request: Request, pk: int) -> Response:
         params = request.query_params
@@ -36,6 +43,13 @@ def get(self, request: Request, pk: int) -> Response:
             lookup, _, to_attr_name = to_attr_spec.partition(":")
             queryset = queryset.prefetch_related(Prefetch(lookup, to_attr=to_attr_name))
 
+        prefetch_select_spec = params.get("prefetch_select")
+        if prefetch_select_spec:
+            lookup, _, sr_field = prefetch_select_spec.partition(":")
+            related_model = _resolve_related_model(Eagle, lookup)
+            child_queryset = related_model.objects.select_related(sr_field)
+            queryset = queryset.prefetch_related(Prefetch(lookup, queryset=child_queryset))
+
         eagle = queryset.get(pk=pk)
 
         data = EagleSerializer(eagle, context={"access": _csv(params.get("access")), "to_attr": to_attr_name}).data

tests/test_unused.py

@@ -1,3 +1,5 @@
+import pytest
+
 from eagle import unused
 from test_project import views
 from test_project.models import Eagle
@@ -78,10 +80,15 @@ def test_to_attr_prefetch_with_rows_accessed_no_warning(self):
 
 
 class TestWarnUnusedNestedPrefetch(BaseRequestTest):
-    def test_nested_prefetched_child_unused_warns_with_propagated_location(self):
+    @pytest.fixture
+    def previous_location_with_climate(self):
+        # Give the eagle a previous location that itself has a climate, so a
+        # ``previous_locations__climates__locations`` chain has rows at every depth.
         previous = LocationFactory(climates=[ClimateFactory()])
         self.graph.eagle.previous_locations.add(previous)
+        return previous
 
+    def test_nested_prefetched_child_unused_warns_with_propagated_location(self, previous_location_with_climate):
         warns = self.request(
             prefetch_related="previous_locations__climates",
             access="previous_locations",
@@ -91,3 +98,40 @@ def test_nested_prefetched_child_unused_warns_with_propagated_location(self):
         assert 'prefetch_related("climates")' in str(warns[0])
         assert "<Location instance>" in str(warns[0])
         assert views.__file__ in str(warns[0])
+
+    def test_depth_three_nested_prefetch_unused_warns(self, previous_location_with_climate):
+        # Prefetch three levels deep but stop reading at the climate level: the
+        # deepest reverse-M2M (``Climate.locations``) is loaded but never accessed.
+        warns = self.request(
+            prefetch_related="previous_locations__climates__locations",
+            access="previous_locations__climates",
+        )
+
+        assert len(warns) == 1
+        assert 'prefetch_related("locations")' in str(warns[0])
+        assert "<Climate instance>" in str(warns[0])
+        assert views.__file__ in str(warns[0])
+
+    def test_depth_three_nested_prefetch_accessed_no_warning(self, previous_location_with_climate):
+        assert (
+            self.request(
+                prefetch_related="previous_locations__climates__locations",
+                access="previous_locations__climates__locations",
+            )
+            == []
+        )
+
+
+class TestWarnUnusedSelectRelatedWithinPrefetch(BaseRequestTest):
+    def test_select_related_within_prefetch_queryset_unused_warns(self):
+        # Prefetch("eaglet", queryset=Eaglet.objects.select_related("eagle")): the prefetched
+        # eaglet is read, but the select_related FK back to its eagle never is.
+        warns = self.request(prefetch_select="eaglet:eagle", access="eaglet")
+
+        assert len(warns) == 1
+        assert 'select_related("eagle")' in str(warns[0])
+        assert "<Eaglet instance>" in str(warns[0])
+        assert views.__file__ in str(warns[0])
+
+    def test_select_related_within_prefetch_queryset_accessed_no_warning(self):
+        assert self.request(prefetch_select="eaglet:eagle", access="eaglet__eagle") == []