From f7a0ff032e52a3c57cd2a8f0f31dde5216b0709a Mon Sep 17 00:00:00 2001
From: Alex Dusenbery <adusenbery@edx.org>
Date: Wed, 21 Feb 2024 16:04:07 -0500
Subject: [PATCH] perf: instance cache and select-related for license
 serialization

---
 license_manager/apps/api/serializers.py      | 15 +++++++++++++++
 license_manager/apps/api/v1/views.py         | 20 ++++++++++++++++++--
 license_manager/apps/subscriptions/models.py |  2 +-
 3 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/license_manager/apps/api/serializers.py b/license_manager/apps/api/serializers.py
index 8e607290..49998b51 100644
--- a/license_manager/apps/api/serializers.py
+++ b/license_manager/apps/api/serializers.py
@@ -1,4 +1,5 @@
 from django.core.validators import MinLengthValidator
+from django.utils.functional import cached_property
 from rest_framework import serializers
 from rest_framework.fields import SerializerMethodField
 
@@ -106,6 +107,7 @@ class MinimalCustomerAgreementSerializer(serializers.ModelSerializer):
     Minimal serializer for the `CustomerAgreement` model that does not
     include information about related subscription plan records.
     """
+    net_days_until_expiration = serializers.SerializerMethodField()
 
     class Meta:
         model = CustomerAgreement
@@ -118,6 +120,19 @@ class Meta:
             'net_days_until_expiration',
         ]
 
+    def get_net_days_until_expiration(self, obj):
+        """
+        Cache the net_days_until_expiration of the agreement
+        to serializer for the lifetime of this serializer instance.
+        """
+        # pylint: disable=attribute-defined-outside-init
+        if hasattr(self, '_cached_net_days_until_expiration'):
+            return self._cached_net_days_until_expiration
+
+        value = obj.net_days_until_expiration
+        self._cached_net_days_until_expiration = value
+        return value
+
 
 class CustomerAgreementSerializer(serializers.ModelSerializer):
     """
diff --git a/license_manager/apps/api/v1/views.py b/license_manager/apps/api/v1/views.py
index 475152af..d7091a52 100644
--- a/license_manager/apps/api/v1/views.py
+++ b/license_manager/apps/api/v1/views.py
@@ -554,6 +554,9 @@ def base_queryset(self):
         return License.objects.filter(
             subscription_plan=self._get_subscription_plan(),
             user_email=self.request.user.email,
+        ).select_related(
+            'subscription_plan',
+            'subscription_plan__customer_agreement',
         ).exclude(
             status=constants.REVOKED
         ).order_by('status', '-subscription_plan__expiration_date')
@@ -562,14 +565,22 @@ def _get_subscription_plan(self):
         """
         Helper that returns the subscription plan specified by `subscription_uuid` in the request.
         """
+        # pylint: disable=attribute-defined-outside-init
+        if hasattr(self, '_cached_subscription_plan'):
+            return self._cached_subscription_plan
+
         subscription_uuid = self.kwargs.get('subscription_uuid')
         if not subscription_uuid:
             return None
 
+        value = None
         try:
-            return SubscriptionPlan.objects.get(uuid=subscription_uuid)
+            value = SubscriptionPlan.objects.get(uuid=subscription_uuid)
         except SubscriptionPlan.DoesNotExist:
-            return None
+            pass
+
+        self._cached_subscription_plan = value
+        return value
 
 
 class LicenseAdminViewSet(BaseLicenseViewSet):
@@ -640,6 +651,11 @@ def base_queryset(self):
         """
         queryset = License.objects.filter(
             subscription_plan=self._get_subscription_plan()
+        ).select_related(
+            'subscription_plan',
+            'subscription_plan__customer_agreement',
+        ).prefetch_related(
+            'subscription_plan__renewal',
         ).order_by(
             'status', 'user_email'
         )
diff --git a/license_manager/apps/subscriptions/models.py b/license_manager/apps/subscriptions/models.py
index 692a314c..597e4ac6 100644
--- a/license_manager/apps/subscriptions/models.py
+++ b/license_manager/apps/subscriptions/models.py
@@ -141,7 +141,7 @@ class CustomerAgreement(TimeStampedModel):
 
     history = HistoricalRecords()
 
-    @property
+    @cached_property
     def net_days_until_expiration(self):
         """
         Returns the max number of days until expiration