Make the annotated rating field in Product and round it in Serializer…

…MethodField

backend/api/products_serializers.py

@@ -1,4 +1,3 @@
-from django.db.models import Avg
 from drf_spectacular.utils import extend_schema_field
 from drf_yasg.utils import swagger_serializer_method
 from rest_framework import serializers
@@ -17,7 +16,7 @@
     Tag,
 )
 
-NO_RATING_MESSAGE = "У данного продукта еще нет оценок."
+RATING_DECIMAL_PLACES = 1
 
 
 class SubcategoryLightSerializer(serializers.ModelSerializer):
@@ -208,12 +207,13 @@ def get_promotion_quantity(self, obj) -> int:
     def get_final_price(self, obj) -> float:
         return obj.final_price
 
-    # TODO: make annotate
     def get_rating(self, obj) -> float:
-        product_reviews = obj.reviews.all()
-        if product_reviews:
-            return round(product_reviews.aggregate(Avg("score"))["score__avg"], 1)
-        return NO_RATING_MESSAGE
+        """Rounds and returns the annotated rating value."""
+        return (
+            round(obj.rating, RATING_DECIMAL_PLACES)
+            if obj.rating is not None
+            else obj.rating
+        )
 
 
 class ProductCreateSerializer(ProductSerializer):

backend/api/products_views.py

@@ -1,4 +1,5 @@
 from django.db import transaction
+from django.db.models import Avg
 from django.shortcuts import get_object_or_404
 from django.utils.decorators import method_decorator
 from django_filters import rest_framework as rf_filters
@@ -504,9 +505,11 @@ class ProductViewSet(DestroyWithPayloadMixin, viewsets.ModelViewSet):
     """Viewset for products."""
 
     http_method_names = ["get", "post", "patch", "delete"]
-    queryset = Product.objects.select_related(
-        "category", "subcategory", "producer"
-    ).prefetch_related("components", "tags", "promotions", "reviews")
+    queryset = (
+        Product.objects.select_related("category", "subcategory", "producer")
+        .prefetch_related("components", "tags", "promotions", "reviews")
+        .annotate(rating=Avg("reviews__score"))
+    )
     serializer_class = ProductSerializer
     permission_classes = [IsAdminOrReadOnly]
     filter_backends = [rf_filters.DjangoFilterBackend]
@@ -523,9 +526,11 @@ def get_serializer_class(self):
         return ProductSerializer
 
     def get_queryset(self):
-        return Product.objects.select_related(
-            "category", "subcategory", "producer"
-        ).prefetch_related("components", "tags", "promotions", "reviews")
+        return (
+            Product.objects.select_related("category", "subcategory", "producer")
+            .prefetch_related("components", "tags", "promotions", "reviews")
+            .annotate(rating=Avg("reviews__score"))
+        )
 
     @transaction.atomic
     def create_delete_or_scold(self, model, product, request):