Дублируется запрос к БД в Django, не могу найти из какого места

Не могу понять из какого места улетает повторный запрос

models

class Product(models.Model):
    name = models.CharField(max_length=150, db_index=True,
                            verbose_name='Название')
    slug = models.SlugField(max_length=150, db_index=True)
    price = models.DecimalField(max_digits=10, decimal_places=2, 
                                verbose_name='Цена')
    category = models.ForeignKey(Category, 
                                 related_name='category',
                                 null=True,
                                 blank=True,
                                 verbose_name='Категория',
                                 on_delete=models.CASCADE,
                                 )
    sales = models.ManyToManyField(Sale, 
                                   related_name='sales',
                                   verbose_name='Скидка',
                                   blank=True
                                   )

class Sale(models.Model):
    name = models.CharField(max_length=150)
    description = models.CharField(max_length=255)
    percent = models.IntegerField(verbose_name='Процент')

    class Meta:
        ordering = ('name', 'percent')
        verbose_name = 'Скидка'
        verbose_name_plural = 'Скидки'

    def __str__(self):
        return self.name

serializers

class ProductSerializer(serializers.ModelSerializer):
    manufacturer = ManufacturerSerializer(read_only=True)
    category = CategorySerializer(read_only=True)
    sales = SaleSerializer(many=True, read_only=True)
    attributes = AttributeSerializer(many=True, read_only=True)

    class Meta:
        model = Product
        fields = ['slug', 'name', 'price', 'sales',
                  'manufacturer', 'category', 'attributes',
                  'is_new', 'is_recomended']

        lookup_field = 'slug'   

class CategorySerializer(serializers.ModelSerializer):
    class Meta:
        model = Category
        fields = ['name', 'parental_category']

view

class ProductsBySales(ListAPIView):
    serializer_class = ProductSerializer
    filterset_fields = ['category']

    def get_queryset(self):
        return Product.objects.prefetch_related('sales', 'attributes').select_related('category', 'manufacturer',).exclude(sales=None)