After using prefetch_related still facing n+1 - django

Question

I am facing multiple duplicate db call even after I am using prefetch_related.
Here is my views:
def index(request):
product_qs = Product.objects.filter(shop_type='Grocery', featured=True, hide=False)
product_list = product_qs.prefetch_related('image', 'size_list').order_by('ranking')
products = terminator(request, product_list, 25) // reusable paginator!
context = {'categories': categories, 'products': products}
return render(request, 'grocery/index.html', context)
Here is my models:
class ProductImage(models.Model):
image = models.ImageField(upload_to='shop/product')
color = models.BooleanField(default=False)
image_thumbnail_index = ImageSpecField(source='image',
processors=[ResizeToFill(308, 412)],
format='JPEG',
options={'quality': 100})
created_at = models.DateTimeField(auto_now_add=True)
updated_at = models.DateTimeField(auto_now=True)
class Product(models.Model):
shop_type = models.CharField(choices=shop_options, max_length=40)
name = models.CharField(max_length=200, unique=True)
image = models.ManyToManyField(ProductImage)
category = TreeForeignKey('Category', null=True, blank=True, on_delete=models.PROTECT)
slug = models.SlugField(max_length=200, db_index=True)
featured = models.BooleanField(default=False)
size = models.BooleanField(default=False)
size_list = models.ManyToManyField(SizeList)
available = models.BooleanField(default=True) # out of stock ?
hide = models.BooleanField(default=False) # archive a product
ranking = models.PositiveIntegerField()
created_at = models.DateTimeField(auto_now_add=True)
updated_at = models.DateTimeField(auto_now=True)
and the template:
<figure class="product-image-container">
<a href="#" class="product-image">
<img src="{{ product.image.first.image_thumbnail_index.url }}" alt="{{ products.name }}">
</a>
{% trans 'Quickview' %}
</figure>
<div class="product-details">
<h2 class="product-title">
<a href="/grocery/product/{{ product.slug }}">
{% if LANGUAGE_CODE == 'en' %}
{{ product.name }}
{% else %}
{{ product.name_bn }}
{% endif %}
</a>
</h2>
<div class="price-box">
<span class="product-price">
{% if LANGUAGE_CODE == 'en' %}
৳ {{ product.price }}
{% else %}
৳ {{ product.price_bn }}
{% endif %}
</span>
</div><!-- End .price-box -->
Screenshot of sql calls:

Answer 1

Since you are already prefetching the ProductImage objects you may use the of the prefetched objects: {% with product.image.all|first as image %}{{ image.image_thumbnail_index.url }}(% endwith %}. (While calling first() does an extra query using LIMIT 1 at the end.)