Support for custom cart item class

.gitignore

@@ -1 +1,3 @@
 *.pyc
+/.project
+/.pydevproject

README.md

@@ -350,3 +350,10 @@ items. By default they are removed from the cart.
 ### Session Key
 
 The `CART_SESSION_KEY` settings controls the name of the session key.
+
+### Customized Cart Item class
+
+The `CART_ITEM_CLASS` settings may contain a dotted path to your extension of
+`carton.cart.CartItem` class (which is the default value). This might get handy
+in case you need some specific pricing model for items (like some discounts for
+ordering more than one entity of the same item).

carton/cart.py

@@ -39,6 +39,7 @@ class Cart(object):
     A cart that lives in the session.
     """
     def __init__(self, session, session_key=None):
+        self.cart_item_class = module_loading.get_cart_item_class()
         self._items_dict = {}
         self.session = session
         self.session_key = session_key or carton_settings.CART_SESSION_KEY
@@ -50,7 +51,7 @@ def __init__(self, session, session_key=None):
             products_queryset = self.get_queryset().filter(pk__in=ids_in_cart)
             for product in products_queryset:
                 item = cart_representation[str(product.pk)]
-                self._items_dict[product.pk] = CartItem(
+                self._items_dict[product.pk] = self.cart_item_class(
                     product, item['quantity'], Decimal(item['price'])
                 )
 
@@ -98,7 +99,8 @@ def add(self, product, price=None, quantity=1):
         else:
             if price == None:
                 raise ValueError('Missing price when adding to cart')
-            self._items_dict[product.pk] = CartItem(product, quantity, price)
+            self._items_dict[product.pk] = self.cart_item_class(
+                    product, quantity, price)
         self.update_session()
 
     def remove(self, product):

carton/module_loading.py

@@ -1,10 +1,26 @@
 from django.conf import settings
 from django.utils.importlib import import_module
 
+from carton import settings as carton_settings
+
+
+def _get_module(dotted_path):
+    """
+    Returns the entity that is imported from dotted path.
+    """
+    package, module = dotted_path.rsplit('.', 1)
+    return getattr(import_module(package), module)
+
 
 def get_product_model():
     """
     Returns the product model that is used by this cart.
     """
-    package, module = settings.CART_PRODUCT_MODEL.rsplit('.', 1)
-    return getattr(import_module(package), module)
+    return _get_module(settings.CART_PRODUCT_MODEL)
+
+
+def get_cart_item_class():
+    """
+    Returns the class that is used by this cart for its items.
+    """
+    return _get_module(carton_settings.CART_ITEM_CLASS)

carton/settings.py

@@ -3,3 +3,5 @@
 CART_SESSION_KEY = getattr(settings, 'CART_SESSION_KEY', 'CART')
 
 CART_TEMPLATE_TAG_NAME = getattr(settings, 'CART_TEMPLATE_TAG_NAME', 'get_cart')
+
+CART_ITEM_CLASS = getattr(settings, 'CART_ITEM_CLASS', 'carton.cart.CartItem')

carton/tests/cart.py

@@ -0,0 +1,22 @@
+from decimal import Decimal
+
+from carton.cart import CartItem
+
+
+class TestCartItem(CartItem):
+    """
+    Customized cart item for unit tests.
+    """
+    _DISCOUNT = 0.2 # 20%
+
+    @property
+    def subtotal(self):
+        """
+        The price for the first item is as earlier, but the price for each next
+        entity of the same item in the cart is lowered for some discount.
+        """
+        if self.quantity == 1:
+            return self.price
+        else:
+            return self.price * Decimal(str(
+                    1 + (self.quantity - 1) * (1 - self._DISCOUNT)))

carton/tests/tests.py

@@ -1,18 +1,21 @@
 from django.core.urlresolvers import reverse
 from django.test import TestCase
+
 from carton.tests.models import Product
+from carton import settings as carton_settings
 
 try:
     from django.test import override_settings
 except ImportError:
     from  django.test.utils import override_settings
 
 
-class CartTests(TestCase):
-
+class BaseTestCase(TestCase):
     def setUp(self):
-        self.deer = Product.objects.create(name='deer', price=10.0, custom_id=1)
-        self.moose = Product.objects.create(name='moose', price=20.0, custom_id=2)
+        self.deer = Product.objects.create(
+                name='deer', price=10.0, custom_id=1)
+        self.moose = Product.objects.create(
+                name='moose', price=20.0, custom_id=2)
         self.url_add = reverse('carton-tests-add')
         self.url_show = reverse('carton-tests-show')
         self.url_remove = reverse('carton-tests-remove')
@@ -22,6 +25,17 @@ def setUp(self):
         self.deer_data = {'product_id': self.deer.pk}
         self.moose_data = {'product_id': self.moose.pk}
 
+    def tearDown(self):
+        # Note that in some tests items might be deleted. Do not try to delete
+        # them twice.
+        if self.deer.pk is not None:
+            self.deer.delete()
+        if self.moose.pk is not None:
+            self.moose.delete()
+
+
+class CartTests(BaseTestCase):
+
     def test_product_is_added(self):
         self.client.post(self.url_add, self.deer_data)
         response = self.client.get(self.url_show)
@@ -115,3 +129,35 @@ def test_custom_product_filter_are_applied(self):
         response = self.client.get(self.url_show)
         self.assertNotContains(response, 'EXCLUDE')
         self.assertContains(response, 'deer')
+
+
+class CustomizedCartItemTests(BaseTestCase):
+    def setUp(self):
+        super(CustomizedCartItemTests, self).setUp()
+        # Note that changing the cart item class with @override_setting
+        # annotation will not work as it was already read in carton_settings
+        self.old_cart_item_class = carton_settings.CART_ITEM_CLASS
+        carton_settings.CART_ITEM_CLASS = 'carton.tests.cart.TestCartItem'
+
+
+    def tearDown(self):
+        carton_settings.CART_ITEM_CLASS = self.old_cart_item_class
+        super(CustomizedCartItemTests, self).tearDown()
+
+
+    def test_custom_cart_item_is_used(self):
+        # We use custom (test) cart item with specific method for total price
+        # calculation, and expect the price to differs for more than one item
+        # of the same type (according to the discount se in that test class).
+
+        self.client.post(self.url_add, self.deer_data)
+        response = self.client.get(self.url_show)
+        # This is still the same as in `test_product_is_added`:
+        self.assertContains(response, '1 deer for $10.0')
+
+        # Now add another one:
+        self.client.post(self.url_add, self.deer_data)
+        response = self.client.get(self.url_show)
+        # And for that one, we should have `TestCartItem.DISCOUNT` applied
+        # (which is 15%):
+        self.assertContains(response, '2 deer for $18.0') # instead of $20.0