Refactor: N+1 query

.env.sample

@@ -6,6 +6,7 @@ DJANGO_SUPERUSER_EMAIL=benefits-admin@calitp.org
 # Django
 DJANGO_STORAGE_DIR=.
 DJANGO_DB_FIXTURES="benefits/core/migrations/local_fixtures.json"
+DJANGO_DEBUG_TOOLBAR=false
 # DJANGO_LOCAL_PORT=
 
 USE_POSTGRES=false

benefits/core/context_processors.py

@@ -44,7 +44,9 @@ def agency(request):
 
 def active_agencies(request):
     """Context processor adds some information about all active agencies to the request context."""
-    agencies = models.TransitAgency.all_active()
+    agencies = models.TransitAgency.all_active().select_related(
+        "transit_processor_config", "transit_processor_config__littlepayconfig", "transit_processor_config__switchioconfig"
+    )
 
     return {"active_agencies": [_agency_context(agency) for agency in agencies]}
 

benefits/core/models/transit.py

@@ -207,7 +207,7 @@ def group_agencies(self, only_active=True):
         """
 
         agencies_in_group = (
-            TransitAgency.objects.filter(transitagencygroup__in=list(self.transitagencygroup_set.all()))
+            TransitAgency.objects.filter(transitagencygroup__in=self.transitagencygroup_set.all())
             .distinct()
             .exclude(pk=self.pk)
         )

benefits/core/session.py

@@ -39,9 +39,17 @@
 
 def agency(request):
     """Get the agency from the request's session, or None"""
+    agency_id = request.session.get(_AGENCY)
+    if not agency_id:
+        return None
+
+    if getattr(request, "_cached_agency", None) and request._cached_agency.id == agency_id:
+        return request._cached_agency
     try:
-        return models.TransitAgency.by_id(request.session[_AGENCY])
-    except (KeyError, models.TransitAgency.DoesNotExist):
+        agency = models.TransitAgency.by_id(agency_id)
+        request._cached_agency = agency
+        return agency
+    except models.TransitAgency.DoesNotExist:
         return None
 
 
@@ -124,9 +132,17 @@ def enrollment_reenrollment(request):
 
 def flow(request) -> models.EnrollmentFlow | None:
     """Get the EnrollmentFlow from the request's session, or None"""
+    flow_id = request.session.get(_FLOW)
+    if not flow_id:
+        return None
+
+    if getattr(request, "_cached_flow", None) and request._cached_flow.id == flow_id:
+        return request._cached_flow
     try:
-        return models.EnrollmentFlow.by_id(request.session[_FLOW])
-    except (KeyError, models.EnrollmentFlow.DoesNotExist):
+        flow = models.EnrollmentFlow.by_id(flow_id)
+        request._cached_flow = flow
+        return flow
+    except models.EnrollmentFlow.DoesNotExist:
         return None
 
 

benefits/settings.py

@@ -23,6 +23,9 @@ def _filter_empty(ls):
 # SECURITY WARNING: don't run with debug turned on in production!
 DEBUG = os.environ.get("DJANGO_DEBUG", "false").lower() == "true"
 
+# SECURITY WARNING: don't run with debug_toolbar turned on in production!
+DEBUG_TOOLBAR = os.environ.get("DJANGO_DEBUG_TOOLBAR", "false").lower() == "true"
+
 ALLOWED_HOSTS = _filter_empty(os.environ.get("DJANGO_ALLOWED_HOSTS", "localhost").split(","))
 
 
@@ -107,6 +110,20 @@ def RUNTIME_ENVIRONMENT():
 if DEBUG:
     MIDDLEWARE.append("benefits.core.middleware.DebugSession")
 
+if DEBUG_TOOLBAR:
+    INSTALLED_APPS.append("debug_toolbar")
+    MIDDLEWARE.insert(0, "debug_toolbar.middleware.DebugToolbarMiddleware")
+    INTERNAL_IPS = ["127.0.0.1"]
+
+    def show_toolbar(request):
+        # Show the toolbar when in local development mode
+        return DEBUG
+
+    DEBUG_TOOLBAR_CONFIG = {
+        "SHOW_TOOLBAR_CALLBACK": show_toolbar,
+    }
+
+
 HEALTHCHECK_USER_AGENTS = _filter_empty(os.environ.get("HEALTHCHECK_USER_AGENTS", "").split(","))
 
 CSRF_COOKIE_AGE = None

benefits/urls.py

@@ -79,6 +79,12 @@ def trigger_csrf(request):
     urlpatterns.append(path("test500/", trigger_500))
     urlpatterns.append(path("testcsrf/", trigger_csrf))
 
+if settings.DEBUG_TOOLBAR:
+    from debug_toolbar.toolbar import debug_toolbar_urls
+
+    urlpatterns.extend(debug_toolbar_urls())
+
+
 if settings.RUNTIME_ENVIRONMENT() in (settings.RUNTIME_ENVS.LOCAL, settings.RUNTIME_ENVS.DEV):
     # simple route to read a pre-defined "secret"
     # this "secret" does not contain sensitive information

pyproject.toml

@@ -35,6 +35,7 @@ dev = [
     "flake8",
     "isort",
     "pre-commit",
+    "django-debug-toolbar"
 ]
 test = [
     "coverage",

tests/pytest/core/test_session.py

@@ -13,6 +13,29 @@
 from benefits.routes import routes
 
 
+@pytest.mark.django_db
+def test_agency_does_not_exist(app_request):
+    app_request.session[session._AGENCY] = -1
+    assert not session.agency(app_request)
+
+
+@pytest.mark.django_db
+def test_agency_cache(model_TransitAgency, app_request):
+    session.update(app_request, agency=model_TransitAgency)
+    assert not hasattr(app_request, "_cached_agency")
+
+    # set _cached_agency
+    first_call = session.agency(app_request)
+
+    assert first_call == model_TransitAgency
+    assert hasattr(app_request, "_cached_agency")
+    assert app_request._cached_agency == model_TransitAgency
+
+    second_call = session.agency(app_request)
+
+    assert second_call == model_TransitAgency
+
+
 @pytest.mark.django_db
 def test_active_agency_False(app_request, model_TransitAgency_inactive):
     session.update(app_request, agency=None)
@@ -132,6 +155,29 @@ def test_enrollment_reenrollment(app_request, model_EnrollmentFlow_supports_expi
     assert session.enrollment_reenrollment(app_request) == expected_reenrollment
 
 
+@pytest.mark.django_db
+def test_flow_does_not_exist(app_request):
+    app_request.session[session._FLOW] = -1
+    assert not session.flow(app_request)
+
+
+@pytest.mark.django_db
+def test_flow_cache(model_EnrollmentFlow, app_request):
+    session.update(app_request, flow=model_EnrollmentFlow)
+    assert not hasattr(app_request, "_cached_flow")
+
+    # set _cached_flow
+    first_call = session.flow(app_request)
+
+    assert first_call == model_EnrollmentFlow
+    assert hasattr(app_request, "_cached_flow")
+    assert app_request._cached_flow == model_EnrollmentFlow
+
+    second_call = session.flow(app_request)
+
+    assert second_call == model_EnrollmentFlow
+
+
 @pytest.mark.django_db
 def test_language_default(app_request):
     assert session.language(app_request) == "en"