Order the related set in a many-to-many relation - django

Question

Lets say I have a setup like this:
class Product(models.Model):
name = models.CharField()
category = models.CharField()
class Shop(models.Model):
name = models.CharField()
website = models.URLField()
class ProductPrices(model.Model):
product = models.ForeignKey(Product)
shop = models.ForeignKey(Shop)
price = models.FloatField()
updated = models.DateTimeField()
and then I have a page on which I would like to list all products, which shops they can be found at and to what prices. Is it possible to have the prices for all (or just some) products sorted, without using:
class Meta:
ordering = ['-price']
on ProductPrices?
That is, in my view I would want to do something like this (sort the productprice_set, on the price column):
def get_queryset(self):
queryset = Product.objects.all()
for product in queryset:
product.productprice_set.order_by('-price')
# Have also tried the following, without any result
product.productprice_set = product.productprice_set.order_by('-price')
return queryset
To clarify: I want to sort the prices for each product, not the products based on the prices. But I want to do this by going "through" the products way.
I want 'productprice_set' ordered, and not 'product'.

Answer 1

That syntax does not somehow modify the relationship so that subsequent calls return an ordered queryset: it returns the ordered qs then and there. Subsequent calls will have the default ordering.
The way to do this is to use the order_by clause when you're retrieving the objects. Since you can't pass arguments to methods in the template, the way to do it is to define a method on Product which returns the ordered prices:
class Product(models.Model):
...
def ordered_prices (self):
return self.productprices_set.order_by('-price')
and call it in the template:
{% for product in products %}
{{ product.name }}
{% for price in product.ordered_prices %}
{% price.price %}
{% endfor %}
{% endfor %}

Answer 2

I have found a solution now in which I don't have to modify any model, nor make any more database queries.
In my view I have now:
def get_queryset(self):
queryset = Product.objects.all().prefetch_related('price_set')
for product in queryset:
product.prices = sorted(product.price_set.all(), key=lambda x: x.price, reverse=true)
return queryset
And then in my template:
{% for product in products %}
{{ product.name }}
{% for price in product.prices %}
{% price.price %}
{% endfor %}
{% endfor %}
Since I'm new to using Django, I wonder if there's anything "wrong" or bad by solving it like this?