On Mon, 2009-02-23 at 16:21 -0800, bendavis78 wrote:
> I have products within categories. The url for a product is /store/
> category-slug/product-slug. My question is about the best way to get
> the url for this product while looping through a product listing
> page. My view simply defines a context variable called products,
> assigned to the results of a .filter() call.
>
> Given these models:
>
> def Category(models.Model):
> name = models.CharField(max_length=255)
> slug = models.SlugField()
>
> def Product(models.Model):
> name = models.CharField(max_length=255)
> slug = models.SlugField()
> category = models.ForeignKey(Category)
>
> def get_absolute_url(self):
> category_slug = Category.objects.get(id=self.category_id).slug
> return "/%s/%s" % (category_slug, self.slug)
>
>
> You can see that calling get_absolute_url() while looping through a
> list of products in a template will require an extra query to be sent
> to the server for each iteration of a product, which is clearly not
> ideal. My other option to use .values() in the view to select out
> the category slug along with all the other columns on the product,
> but this doesn't seem ideal either.
You can certainly simplify get_absolute_url() a bit:
def get_absolute_url(self):
category_slug = self.category__slug
return "/%s/%s" % (category_slug, self.slug)
In this way, if it needs to, Django will look up the related model.
However, if you've retrieved a queryset using select_related(), the
Category instances will already be present and no extra query will be
involved. If you're doing a loop and needing get_absolute_url, you then
have to remember to always use select_related().
You could even make that automatic by creating a custom default manager
whose get_query_set() method looked like this:
def get_query_set(self):
return super(MyManager,
self).get_query_set().select_related()
and it would always happen.
Regards,
Malcolm
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