refactor(likes): Make like/unlike operations atomic

Wrap the like and unlike logic in `django.db.transaction.atomic()` to ensure that the creation/deletion of the like and the update of the promo's `like_count` are performed as a single, indivisible operation. This prevents potential race conditions and data  inconsistency.

Add `promo.refresh_from_db()` after the `F()` expression update to ensure the promo object reflects the latest database state.

Author: RandomProgramm3r

promo_code/user/views.py

@@ -246,42 +246,46 @@ def get_promo_object(self, promo_id):
 
     def post(self, request, id):
         """Add a like to the promo code."""
-        promo = self.get_promo_object(id)
+        with django.db.transaction.atomic():
+            promo = self.get_promo_object(id)
 
-        created = user.models.PromoLike.objects.get_or_create(
-            user=request.user,
-            promo=promo,
-        )
+            like_obj, created = user.models.PromoLike.objects.get_or_create(
+                user=request.user,
+                promo=promo,
+            )
 
-        if created:
-            promo.like_count = django.db.models.F('like_count') + 1
-            promo.save(update_fields=['like_count'])
+            if created:
+                promo.like_count = django.db.models.F('like_count') + 1
+                promo.save(update_fields=['like_count'])
+                promo.refresh_from_db()
 
-        return rest_framework.response.Response(
-            {'status': 'ok'},
-            status=rest_framework.status.HTTP_200_OK,
-        )
+            return rest_framework.response.Response(
+                {'status': 'ok'},
+                status=rest_framework.status.HTTP_200_OK,
+            )
 
     def delete(self, request, id):
         """Remove a like from the promo code."""
-        promo = self.get_promo_object(id)
+        with django.db.transaction.atomic():
+            promo = self.get_promo_object(id)
+
+            # Idempotency: if the like doesn't exist,
+            # do nothing and still return 200 OK.
+            like_instance = user.models.PromoLike.objects.filter(
+                user=request.user,
+                promo=promo,
+            ).first()
+
+            if like_instance:
+                like_instance.delete()
+                promo.like_count = django.db.models.F('like_count') - 1
+                promo.save(update_fields=['like_count'])
+                promo.refresh_from_db()
 
-        # Idempotency: if the like doesn't exist,
-        # do nothing and still return 200 OK.
-        like_instance = user.models.PromoLike.objects.filter(
-            user=request.user,
-            promo=promo,
-        ).first()
-
-        if like_instance:
-            like_instance.delete()
-            promo.like_count = django.db.models.F('like_count') - 1
-            promo.save(update_fields=['like_count'])
-
-        return rest_framework.response.Response(
-            {'status': 'ok'},
-            status=rest_framework.status.HTTP_200_OK,
-        )
+            return rest_framework.response.Response(
+                {'status': 'ok'},
+                status=rest_framework.status.HTTP_200_OK,
+            )
 
 
 class PromoCommentListCreateView(rest_framework.generics.ListCreateAPIView):