fix: serializer no longer crashes on bad data

This protection against crashing is nice because we use the serializer
in django admin, so bad data also crashes django admin.

enterprise_access/apps/api/serializers/subsidy_access_policy.py

@@ -10,6 +10,7 @@
 from drf_spectacular.utils import extend_schema_field
 from opaque_keys import InvalidKeyError
 from opaque_keys.edx.keys import CourseKey
+from requests.exceptions import HTTPError
 from rest_framework import serializers
 
 from enterprise_access.apps.subsidy_access_policy.constants import CENTS_PER_DOLLAR, PolicyTypes
@@ -64,9 +65,8 @@ class SubsidyAccessPolicyAggregatesSerializer(serializers.Serializer):
             f"Total amount allocated for policies of type {PolicyTypes.ASSIGNED_LEARNER_CREDIT} (0 otherwise), in USD.",
         ),
     )
-    spend_available_usd_cents = serializers.IntegerField(
+    spend_available_usd_cents = serializers.SerializerMethodField(
         help_text="Total Amount of available spend for policy, in positive USD cents.",
-        source="spend_available",
     )
     spend_available_usd = serializers.SerializerMethodField(
         help_text="Total Amount of available spend for policy, in USD.",
@@ -76,8 +76,12 @@ class SubsidyAccessPolicyAggregatesSerializer(serializers.Serializer):
     def get_amount_redeemed_usd_cents(self, policy):
         """
         Make amount a positive number.
+        Protect against Subsidy API Errors.
         """
-        return policy.total_redeemed * -1
+        try:
+            return policy.total_redeemed * -1
+        except HTTPError:
+            return 0
 
     @extend_schema_field(serializers.IntegerField)
     def get_amount_allocated_usd_cents(self, policy):
@@ -86,17 +90,46 @@ def get_amount_allocated_usd_cents(self, policy):
         """
         return policy.total_allocated * -1
 
+    @extend_schema_field(serializers.IntegerField)
+    def get_spend_available_usd_cents(self, policy):
+        """
+        Protect against Subsidy API Errors.
+        """
+        try:
+            return policy.spend_available
+        except HTTPError:
+            return 0
+
     @extend_schema_field(serializers.FloatField)
     def get_amount_redeemed_usd(self, policy):
-        return float(policy.total_redeemed * -1) / CENTS_PER_DOLLAR
+        """
+        Make amount a positive number.
+        Convert cents to dollars.
+        Protect against Subsidy API Errors.
+        """
+        try:
+            return float(policy.total_redeemed * -1) / CENTS_PER_DOLLAR
+        except HTTPError:
+            return 0
 
     @extend_schema_field(serializers.FloatField)
     def get_amount_allocated_usd(self, policy):
+        """
+        Make amount a positive number.
+        Convert cents to dollars.
+        """
         return float(policy.total_allocated * -1) / CENTS_PER_DOLLAR
 
     @extend_schema_field(serializers.FloatField)
     def get_spend_available_usd(self, policy):
-        return float(policy.spend_available) / CENTS_PER_DOLLAR
+        """
+        Convert cents to dollars.
+        Protect against Subsidy API Errors.
+        """
+        try:
+            return float(policy.spend_available) / CENTS_PER_DOLLAR
+        except HTTPError:
+            return 0
 
 
 class SubsidyAccessPolicyResponseSerializer(serializers.ModelSerializer):

enterprise_access/apps/subsidy_access_policy/models.py

@@ -336,6 +336,9 @@ def spend_available(self):
 
         Returns:
             int: quantity >= 0 of USD Cents representing the policy-wide spend available.
+
+        Raises:
+            requests.exceptions.HTTPError if the request to Subsidy API (to fetch aggregates) fails.
         """
         # This is how much available spend the policy limit would allow, ignoring the subsidy balance.
         if self.spend_limit is not None:
@@ -354,6 +357,9 @@ def total_redeemed(self):
 
         Returns:
             int: quantity <= 0 of USD Cents.
+
+        Raises:
+            requests.exceptions.HTTPError if the request to Subsidy API (to fetch aggregates) fails.
         """
         return self.aggregates_for_policy().get('total_quantity') or 0
 
@@ -406,6 +412,9 @@ def get_content_price(self, content_key, content_metadata=None):
     def aggregates_for_policy(self):
         """
         Returns aggregate transaction data for this policy.
+
+        Raises:
+            requests.exceptions.HTTPError if the request to Subsidy API fails.
         """
         response_payload = self.subsidy_client.list_subsidy_transactions(
             subsidy_uuid=self.subsidy_uuid,