caching_querysets.py

# instantiates a queryset and cache is empty.
product = Product.objects.get(id=5)

# Category object is retrieved from the database at this point 
# and the results are saved in queryset's cache.
product.category

# retrieved from the cached results.
product.category


# callable attributes queries database every sigle time
product.categories.all()  # query performed using db
product.categories.all()  # query performed again using db