Hierarchical product URL support.

Adds the new setting SHOP_USE_HIERARCHICAL_URLS (default disabled).  When
enabled, a product URL is determined as follows:

  - If the product belongs to exactly one category, the product's URL will be:
      <category-slug>/<product-slug>/<product-id>

  - Otherwise, the product's URL will be as before:
      product/<product-slug>

cartridge/shop/defaults.py

@@ -293,3 +293,12 @@
     editable=False,
     default=True,
 )
+
+register_setting(
+    name="SHOP_USE_HIERARCHICAL_URLS",
+    label=_("Use hierarchical product URLs"),
+    description="If set and a product only belongs to a single category, "
+        "generate the product's URL in terms of that category.",
+    editable=False,
+    default=False,
+)

cartridge/shop/models.py

@@ -128,8 +128,25 @@ def save(self, *args, **kwargs):
 
     @models.permalink
     def get_absolute_url(self):
+        if settings.SHOP_USE_HIERARCHICAL_URLS:
+            category = self.get_category()
+            if category:
+                return ("shop_category_product", (), {
+                    "category_slug": category.get_raw_slug(),
+                    "slug": self.slug,
+                    "product_id": self.id})
         return ("shop_product", (), {"slug": self.slug})
 
+    def get_category(self):
+        """
+        Returns the single category this product is associated with, or None
+        if the number of categories is not exactly 1.
+        """
+        categories = self.categories.all()
+        if len(categories) == 1:
+            return categories[0]
+        return None
+
     def copy_default_variation(self):
         """
         Copies the price and image fields from the default variation
@@ -380,6 +397,14 @@ def filters(self):
             return reduce(operator, filters)
         return products
 
+    def get_raw_slug(self):
+        """
+        Returns this object's slug stripped of its parent's slug.
+        """
+        if not self.parent or not self.parent.slug:
+            return self.slug
+        return self.slug.lstrip(self.parent.slug).lstrip('/')
+
 
 class Order(models.Model):
 

cartridge/shop/urls.py

@@ -8,4 +8,6 @@
     url("^checkout/$", "checkout_steps", name="shop_checkout"),
     url("^checkout/complete/$", "complete", name="shop_complete"),
     url("^invoice/(?P<order_id>\d+)/$", "invoice", name="shop_invoice"),
+    url("^(?P<category_slug>.+)/(?P<slug>.+)/(?P<product_id>\d+)$",
+        "category_product", name="shop_category_product"),
 )

cartridge/shop/views.py

@@ -31,13 +31,15 @@
 order_handler = handler(settings.SHOP_HANDLER_ORDER)
 
 
-def product(request, slug, template="shop/product.html"):
+def product(request, slug, template="shop/product.html", product=None):
     """
     Display a product - convert the product variations to JSON as well as
     handling adding the product to either the cart or the wishlist.
     """
-    published_products = Product.objects.published(for_user=request.user)
-    product = get_object_or_404(published_products, slug=slug)
+    if not product:
+        published_products = Product.objects.published(for_user=request.user)
+        product = get_object_or_404(published_products, slug=slug)
+
     fields = [f.name for f in ProductVariation.option_fields()]
     variations = product.variations.all()
     variations_json = simplejson.dumps([dict([(f, getattr(v, f))
@@ -81,6 +83,25 @@ def product(request, slug, template="shop/product.html"):
     }
     return render(request, template, context)
 
+def category_product(request, category_slug, slug, product_id,
+        template="shop/product.html"):
+    """
+    Display a product in terms of its category's slug.  Wrapper around
+    product().  Only enabled when SHOP_USE_HIERARCHICAL_URLS is True.
+    """
+    published_products = Product.objects.published(for_user=request.user)
+    product_obj = get_object_or_404(published_products, id=product_id)
+    category = product_obj.get_category()
+
+    # Tolerate stale URLs by redirecting to the new URL.
+    if not settings.SHOP_USE_HIERARCHICAL_URLS or not category:
+        # Setting is disabled or category has been removed.
+        return redirect(product_obj.get_absolute_url(), permanent=True)
+    elif slug != product_obj.slug or category_slug != category.get_raw_slug():
+        # Category or product slug mismatch.
+        return redirect(product_obj.get_absolute_url(), permanent=True)
+
+    return product(request, slug, template=template, product=product_obj)
 
 @never_cache
 def wishlist(request, template="shop/wishlist.html"):