Merge branch 'batch_cache'

registrasion/controllers/batch.py

@@ -0,0 +1,119 @@
+import contextlib
+import functools
+
+from django.contrib.auth.models import User
+
+
+class BatchController(object):
+    ''' Batches are sets of operations where certain queries for users may be
+    repeated, but are also unlikely change within the boundaries of the batch.
+
+    Batches are keyed per-user. You can mark the edge of the batch with the
+    ``batch`` context manager. If you nest calls to ``batch``, only the
+    outermost call will have the effect of ending the batch.
+
+    Batches store results for functions wrapped with ``memoise``. These results
+    for the user are flushed at the end of the batch.
+
+    If a return for a memoised function has a callable attribute called
+    ``end_batch``, that attribute will be called at the end of the batch.
+
+    '''
+
+    _user_caches = {}
+    _NESTING_KEY = "nesting_count"
+
+    @classmethod
+    @contextlib.contextmanager
+    def batch(cls, user):
+        ''' Marks the entry point for a batch for the given user. '''
+
+        cls._enter_batch_context(user)
+        try:
+            yield
+        finally:
+            # Make sure we clean up in case of errors.
+            cls._exit_batch_context(user)
+
+    @classmethod
+    def _enter_batch_context(cls, user):
+        if user not in cls._user_caches:
+            cls._user_caches[user] = cls._new_cache()
+
+        cache = cls._user_caches[user]
+        cache[cls._NESTING_KEY] += 1
+
+    @classmethod
+    def _exit_batch_context(cls, user):
+        cache = cls._user_caches[user]
+        cache[cls._NESTING_KEY] -= 1
+
+        if cache[cls._NESTING_KEY] == 0:
+            cls._call_end_batch_methods(user)
+            del cls._user_caches[user]
+
+    @classmethod
+    def _call_end_batch_methods(cls, user):
+        cache = cls._user_caches[user]
+        ended = set()
+        while True:
+            keys = set(cache.keys())
+            if ended == keys:
+                break
+            keys_to_end = keys - ended
+            for key in keys_to_end:
+                item = cache[key]
+                if hasattr(item, 'end_batch') and callable(item.end_batch):
+                    item.end_batch()
+            ended = ended | keys_to_end
+
+    @classmethod
+    def memoise(cls, func):
+        ''' Decorator that stores the result of the stored function in the
+        user's results cache until the batch completes. Keyword arguments are
+        not yet supported.
+
+        Arguments:
+            func (callable(*a)): The function whose results we want
+                to store. The positional arguments, ``a``, are used as cache
+                keys.
+
+        Returns:
+            callable(*a): The memosing version of ``func``.
+
+        '''
+
+        @functools.wraps(func)
+        def f(*a):
+
+            for arg in a:
+                if isinstance(arg, User):
+                    user = arg
+                    break
+            else:
+                raise ValueError("One position argument must be a User")
+
+            func_key = (func, tuple(a))
+            cache = cls.get_cache(user)
+
+            if func_key not in cache:
+                cache[func_key] = func(*a)
+
+            return cache[func_key]
+
+        return f
+
+    @classmethod
+    def get_cache(cls, user):
+        if user not in cls._user_caches:
+            # Return blank cache here, we'll just discard :)
+            return cls._new_cache()
+
+        return cls._user_caches[user]
+
+    @classmethod
+    def _new_cache(cls):
+        ''' Returns a new cache dictionary. '''
+        cache = {}
+        cache[cls._NESTING_KEY] = 0
+        return cache

registrasion/controllers/cart.py

@@ -16,6 +16,7 @@ from registrasion.models import commerce
 from registrasion.models import conditions
 from registrasion.models import inventory
 
+from.batch import BatchController
 from .category import CategoryController
 from .discount import DiscountController
 from .flag import FlagController
@@ -34,10 +35,11 @@ def _modifies_cart(func):
     def inner(self, *a, **k):
         self._fail_if_cart_is_not_active()
         with transaction.atomic():
-            with CartController.operations_batch(self.cart.user) as mark:
+            with BatchController.batch(self.cart.user):
-                mark.mark = True  # Marker that we've modified the cart
+                # Mark the version of self in the batch cache as modified
+                memoised = self.for_user(self.cart.user)
+                memoised._modified_by_batch = True
                 return func(self, *a, **k)
-
     return inner
 
 
@@ -47,6 +49,7 @@ class CartController(object):
         self.cart = cart
 
     @classmethod
+    @BatchController.memoise
     def for_user(cls, user):
         ''' Returns the user's current cart, or creates a new cart
         if there isn't one ready yet. '''
@@ -64,59 +67,6 @@ class CartController(object):
             )
         return cls(existing)
 
-    # Marks the carts that are currently in batches
-    _FOR_USER = {}
-    _BATCH_COUNT = collections.defaultdict(int)
-    _MODIFIED_CARTS = set()
-
-    class _ModificationMarker(object):
-        pass
-
-    @classmethod
-    @contextlib.contextmanager
-    def operations_batch(cls, user):
-        ''' Marks the boundary for a batch of operations on a user's cart.
-
-        These markers can be nested. Only on exiting the outermost marker will
-        a batch be ended.
-
-        When a batch is ended, discounts are recalculated, and the cart's
-        revision is increased.
-        '''
-
-        if user not in cls._FOR_USER:
-            _ctrl = cls.for_user(user)
-            cls._FOR_USER[user] = (_ctrl, _ctrl.cart.id)
-
-        ctrl, _id = cls._FOR_USER[user]
-
-        cls._BATCH_COUNT[_id] += 1
-        try:
-            success = False
-
-            marker = cls._ModificationMarker()
-            yield marker
-
-            if hasattr(marker, "mark"):
-                cls._MODIFIED_CARTS.add(_id)
-
-            success = True
-        finally:
-
-            cls._BATCH_COUNT[_id] -= 1
-
-            # Only end on the outermost batch marker, and only if
-            # it excited cleanly, and a modification occurred
-            modified = _id in cls._MODIFIED_CARTS
-            outermost = cls._BATCH_COUNT[_id] == 0
-            if modified and outermost and success:
-                ctrl._end_batch()
-                cls._MODIFIED_CARTS.remove(_id)
-
-            # Clear out the cache on the outermost operation
-            if outermost:
-                del cls._FOR_USER[user]
-
     def _fail_if_cart_is_not_active(self):
         self.cart.refresh_from_db()
         if self.cart.status != commerce.Cart.STATUS_ACTIVE:
@@ -144,6 +94,13 @@ class CartController(object):
         self.cart.time_last_updated = timezone.now()
         self.cart.reservation_duration = max(reservations)
 
+
+    def end_batch(self):
+        ''' Calls ``_end_batch`` if a modification has been performed in the
+        previous batch. '''
+        if hasattr(self,'_modified_by_batch'):
+            self._end_batch()
+
     def _end_batch(self):
         ''' Performs operations that occur occur at the end of a batch of
         product changes/voucher applications etc.
@@ -217,16 +174,14 @@ class CartController(object):
         errors = []
 
         # Pre-annotate products
-        products = [p for (p, q) in product_quantities]
+        remainders = ProductController.user_remainders(self.cart.user)
-        r = ProductController.attach_user_remainders(self.cart.user, products)
-        with_remainders = dict((p, p) for p in r)
 
         # Test each product limit here
         for product, quantity in product_quantities:
             if quantity < 0:
                 errors.append((product, "Value must be zero or greater."))
 
-            limit = with_remainders[product].remainder
+            limit = remainders[product.id]
 
             if quantity > limit:
                 errors.append((
@@ -242,12 +197,11 @@ class CartController(object):
             by_cat[product.category].append((product, quantity))
 
         # Pre-annotate categories
-        r = CategoryController.attach_user_remainders(self.cart.user, by_cat)
+        remainders = CategoryController.user_remainders(self.cart.user)
-        with_remainders = dict((cat, cat) for cat in r)
 
         # Test each category limit here
         for category in by_cat:
-            limit = with_remainders[category].remainder
+            limit = remainders[category.id]
 
             # Get the amount so far in the cart
             to_add = sum(i[1] for i in by_cat[category])

registrasion/controllers/category.py

@@ -7,6 +7,7 @@ from django.db.models import Sum
 from django.db.models import When
 from django.db.models import Value
 
+from .batch import BatchController
 
 class AllProducts(object):
     pass
@@ -39,17 +40,17 @@ class CategoryController(object):
         return set(i.category for i in available)
 
     @classmethod
-    def attach_user_remainders(cls, user, categories):
+    @BatchController.memoise
+    def user_remainders(cls, user):
         '''
 
         Return:
-            queryset(inventory.Product): A queryset containing items from
+            Mapping[int->int]: A dictionary that maps the category ID to the
-            ``categories``, with an extra attribute -- remainder = the amount
+            user's remainder for that category.
-            of items from this category that is remaining.
+
         '''
 
-        ids = [category.id for category in categories]
+        categories = inventory.Category.objects.all()
-        categories = inventory.Category.objects.filter(id__in=ids)
 
         cart_filter = (
             Q(product__productitem__cart__user=user) &
@@ -73,12 +74,4 @@ class CategoryController(object):
 
         categories = categories.annotate(remainder=remainder)
 
-        return categories
+        return dict((cat.id, cat.remainder) for cat in categories)
-
-    def user_quantity_remaining(self, user):
-        ''' Returns the quantity of this product that the user add in the
-        current cart. '''
-
-        with_remainders = self.attach_user_remainders(user, [self.category])
-
-        return with_remainders[0].remainder

registrasion/controllers/discount.py

@@ -1,6 +1,8 @@
 import itertools
 
-from conditions import ConditionController
+from .batch import BatchController
+from .conditions import ConditionController
+
 from registrasion.models import commerce
 from registrasion.models import conditions
 
@@ -10,7 +12,6 @@ from django.db.models import Sum
 from django.db.models import Value
 from django.db.models import When
 
-
 class DiscountAndQuantity(object):
     ''' Represents a discount that can be applied to a product or category
     for a given user.
@@ -50,7 +51,22 @@ class DiscountController(object):
         categories and products. The discounts also list the available quantity
         for this user, not including products that are pending purchase. '''
 
-        filtered_clauses = cls._filtered_discounts(user, categories, products)
+        filtered_clauses = cls._filtered_clauses(user)
+
+        # clauses that match provided categories
+        categories = set(categories)
+        # clauses that match provided products
+        products = set(products)
+        # clauses that match categories for provided products
+        product_categories = set(product.category for product in products)
+        # (Not relevant: clauses that match products in provided categories)
+        all_categories = categories | product_categories
+
+        filtered_clauses = (
+            clause for clause in filtered_clauses
+            if hasattr(clause, 'product') and clause.product in products or
+            hasattr(clause, 'category') and clause.category in all_categories
+        )
 
         discounts = []
 
@@ -84,12 +100,13 @@ class DiscountController(object):
         return discounts
 
     @classmethod
-    def _filtered_discounts(cls, user, categories, products):
+    @BatchController.memoise
+    def _filtered_clauses(cls, user):
         '''
 
         Returns:
-            Sequence[discountbase]: All discounts that passed the filter
+            Sequence[DiscountForProduct | DiscountForCategory]: All clauses
-            function.
+            that passed the filter function.
 
         '''
 
@@ -98,42 +115,22 @@ class DiscountController(object):
             i for i in types if issubclass(i, conditions.DiscountBase)
         ]
 
-        # discounts that match provided categories
+        product_clauses = conditions.DiscountForProduct.objects.all()
-        category_discounts = conditions.DiscountForCategory.objects.filter(
+        product_clauses = product_clauses.select_related(
-            category__in=categories
+            "discount",
-        )
-        # discounts that match provided products
-        product_discounts = conditions.DiscountForProduct.objects.filter(
-            product__in=products
-        )
-        # discounts that match categories for provided products
-        product_category_discounts = conditions.DiscountForCategory.objects
-        product_category_discounts = product_category_discounts.filter(
-            category__in=(product.category for product in products)
-        )
-        # (Not relevant: discounts that match products in provided categories)
-
-        product_discounts = product_discounts.select_related(
             "product",
             "product__category",
         )
-
+        category_clauses = conditions.DiscountForCategory.objects.all()
-        all_category_discounts = (
+        category_clauses = category_clauses.select_related(
-            category_discounts | product_category_discounts
-        )
-        all_category_discounts = all_category_discounts.select_related(
             "category",
-        )
+            "discount",
-
-        valid_discounts = conditions.DiscountBase.objects.filter(
-            Q(discountforproduct__in=product_discounts) |
-            Q(discountforcategory__in=all_category_discounts)
         )
 
         all_subsets = []
 
         for discounttype in discounttypes:
-            discounts = discounttype.objects.filter(id__in=valid_discounts)
+            discounts = discounttype.objects.all()
             ctrl = ConditionController.for_type(discounttype)
             discounts = ctrl.pre_filter(discounts, user)
             all_subsets.append(discounts)
@@ -145,8 +142,8 @@ class DiscountController(object):
         from_filter = dict((i.id, i) for i in filtered_discounts)
 
         clause_sets = (
-            product_discounts.filter(discount__in=filtered_discounts),
+            product_clauses.filter(discount__in=filtered_discounts),
-            all_category_discounts.filter(discount__in=filtered_discounts),
+            category_clauses.filter(discount__in=filtered_discounts),
         )
 
         clause_sets = (

registrasion/controllers/flag.py

@@ -6,6 +6,7 @@ from collections import namedtuple
 from django.db.models import Count
 from django.db.models import Q
 
+from .batch import BatchController
 from .conditions import ConditionController
 
 from registrasion.models import conditions
@@ -47,8 +48,6 @@ class FlagController(object):
         a list is returned containing all of the products that are *not
         enabled*. '''
 
-        print "GREPME: test_flags()"
-
         if products is not None and product_quantities is not None:
             raise ValueError("Please specify only products or "
                              "product_quantities")
@@ -62,7 +61,7 @@ class FlagController(object):
 
         if products:
             # Simplify the query.
-            all_conditions = cls._filtered_flags(user, products)
+            all_conditions = cls._filtered_flags(user)
         else:
             all_conditions = []
 
@@ -86,6 +85,8 @@ class FlagController(object):
             # from the categories covered by this condition
 
             ids = [product.id for product in products]
+
+            # TODO: This is re-evaluated a lot.
             all_products = inventory.Product.objects.filter(id__in=ids)
             cond = (
                 Q(flagbase_set=condition) |
@@ -117,7 +118,7 @@ class FlagController(object):
                 if not met and product not in messages:
                     messages[product] = message
 
-        total_flags = FlagCounter.count()
+        total_flags = FlagCounter.count(user)
 
         valid = {}
 
@@ -160,7 +161,8 @@ class FlagController(object):
         return error_fields
 
     @classmethod
-    def _filtered_flags(cls, user, products):
+    @BatchController.memoise
+    def _filtered_flags(cls, user):
         '''
 
         Returns:
@@ -171,26 +173,15 @@ class FlagController(object):
         types = list(ConditionController._controllers())
         flagtypes = [i for i in types if issubclass(i, conditions.FlagBase)]
 
-        # Get all flags for the products and categories.
-        prods = (
-            product.flagbase_set.all()
-            for product in products
-        )
-        cats = (
-            category.flagbase_set.all()
-            for category in set(product.category for product in products)
-        )
-        all_flags = reduce(operator.or_, itertools.chain(prods, cats))
-
         all_subsets = []
 
         for flagtype in flagtypes:
-            flags = flagtype.objects.filter(id__in=all_flags)
+            flags = flagtype.objects.all()
             ctrl = ConditionController.for_type(flagtype)
             flags = ctrl.pre_filter(flags, user)
             all_subsets.append(flags)
 
-        return itertools.chain(*all_subsets)
+        return list(itertools.chain(*all_subsets))
 
 
 ConditionAndRemainder = namedtuple(
@@ -220,11 +211,11 @@ _ConditionsCount = namedtuple(
 )
 
 
-# TODO: this should be cacheable.
 class FlagCounter(_FlagCounter):
 
     @classmethod
-    def count(cls):
+    @BatchController.memoise
+    def count(cls, user):
         # Get the count of how many conditions should exist per product
         flagbases = conditions.FlagBase.objects
 

registrasion/controllers/product.py

@@ -9,6 +9,7 @@ from django.db.models import Value
 from registrasion.models import commerce
 from registrasion.models import inventory
 
+from .batch import BatchController
 from .category import CategoryController
 from .flag import FlagController
 
@@ -34,18 +35,14 @@ class ProductController(object):
         if products is not None:
             all_products = set(itertools.chain(all_products, products))
 
-        categories = set(product.category for product in all_products)
+        category_remainders = CategoryController.user_remainders(user)
-        r = CategoryController.attach_user_remainders(user, categories)
+        product_remainders = ProductController.user_remainders(user)
-        cat_quants = dict((c, c) for c in r)
-
-        r = ProductController.attach_user_remainders(user, all_products)
-        prod_quants = dict((p, p) for p in r)
 
         passed_limits = set(
             product
             for product in all_products
-            if cat_quants[product.category].remainder > 0
+            if category_remainders[product.category.id] > 0
-            if prod_quants[product].remainder > 0
+            if product_remainders[product.id] > 0
         )
 
         failed_and_messages = FlagController.test_flags(
@@ -59,17 +56,16 @@ class ProductController(object):
         return out
 
     @classmethod
-    def attach_user_remainders(cls, user, products):
+    @BatchController.memoise
+    def user_remainders(cls, user):
         '''
 
         Return:
-            queryset(inventory.Product): A queryset containing items from
+            Mapping[int->int]: A dictionary that maps the product ID to the
-            ``product``, with an extra attribute -- remainder = the amount of
+            user's remainder for that product.
-            this item that is remaining.
         '''
 
-        ids = [product.id for product in products]
+        products = inventory.Product.objects.all()
-        products = inventory.Product.objects.filter(id__in=ids)
 
         cart_filter = (
             Q(productitem__cart__user=user) &
@@ -93,12 +89,4 @@ class ProductController(object):
 
         products = products.annotate(remainder=remainder)
 
-        return products
+        return dict((product.id, product.remainder) for product in products)
-
-    def user_quantity_remaining(self, user):
-        ''' Returns the quantity of this product that the user add in the
-        current cart. '''
-
-        with_remainders = self.attach_user_remainders(user, [self.product])
-
-        return with_remainders[0].remainder

registrasion/tests/test_batch.py

@@ -0,0 +1,144 @@
+import datetime
+import pytz
+
+from django.core.exceptions import ValidationError
+
+from controller_helpers import TestingCartController
+from test_cart import RegistrationCartTestCase
+
+from registrasion.controllers.batch import BatchController
+from registrasion.controllers.discount import DiscountController
+from registrasion.controllers.product import ProductController
+from registrasion.models import commerce
+from registrasion.models import conditions
+
+UTC = pytz.timezone('UTC')
+
+
+class BatchTestCase(RegistrationCartTestCase):
+
+    def test_no_caches_outside_of_batches(self):
+        cache_1 = BatchController.get_cache(self.USER_1)
+        cache_2 = BatchController.get_cache(self.USER_2)
+
+        # Identity testing is important here
+        self.assertIsNot(cache_1, cache_2)
+
+    def test_cache_clears_at_batch_exit(self):
+        with BatchController.batch(self.USER_1):
+            cache_1 = BatchController.get_cache(self.USER_1)
+
+        cache_2 = BatchController.get_cache(self.USER_1)
+
+        self.assertIsNot(cache_1, cache_2)
+
+    def test_caches_identical_within_nestings(self):
+        with BatchController.batch(self.USER_1):
+            cache_1 = BatchController.get_cache(self.USER_1)
+
+            with BatchController.batch(self.USER_2):
+                cache_2 = BatchController.get_cache(self.USER_1)
+
+            cache_3 = BatchController.get_cache(self.USER_1)
+
+        self.assertIs(cache_1, cache_2)
+        self.assertIs(cache_2, cache_3)
+
+    def test_caches_are_independent_for_different_users(self):
+        with BatchController.batch(self.USER_1):
+            cache_1 = BatchController.get_cache(self.USER_1)
+
+            with BatchController.batch(self.USER_2):
+                cache_2 = BatchController.get_cache(self.USER_2)
+
+        self.assertIsNot(cache_1, cache_2)
+
+    def test_cache_clears_are_independent_for_different_users(self):
+        with BatchController.batch(self.USER_1):
+            cache_1 = BatchController.get_cache(self.USER_1)
+
+            with BatchController.batch(self.USER_2):
+                cache_2 = BatchController.get_cache(self.USER_2)
+
+            with BatchController.batch(self.USER_2):
+                cache_3 = BatchController.get_cache(self.USER_2)
+
+            cache_4 = BatchController.get_cache(self.USER_1)
+
+        self.assertIs(cache_1, cache_4)
+        self.assertIsNot(cache_1, cache_2)
+        self.assertIsNot(cache_2, cache_3)
+
+    def test_new_caches_for_new_batches(self):
+        with BatchController.batch(self.USER_1):
+            cache_1 = BatchController.get_cache(self.USER_1)
+
+        with BatchController.batch(self.USER_1):
+            cache_2 = BatchController.get_cache(self.USER_1)
+
+            with BatchController.batch(self.USER_1):
+                cache_3 = BatchController.get_cache(self.USER_1)
+
+        self.assertIs(cache_2, cache_3)
+        self.assertIsNot(cache_1, cache_2)
+
+    def test_memoisation_happens_in_batch_context(self):
+        with BatchController.batch(self.USER_1):
+            output_1 = self._memoiseme(self.USER_1)
+
+            with BatchController.batch(self.USER_1):
+                output_2 = self._memoiseme(self.USER_1)
+
+        self.assertIs(output_1, output_2)
+
+    def test_memoisaion_does_not_happen_outside_batch_context(self):
+        output_1 = self._memoiseme(self.USER_1)
+        output_2 = self._memoiseme(self.USER_1)
+
+        self.assertIsNot(output_1, output_2)
+
+    def test_memoisation_is_user_independent(self):
+        with BatchController.batch(self.USER_1):
+            output_1 = self._memoiseme(self.USER_1)
+            with BatchController.batch(self.USER_2):
+                output_2 = self._memoiseme(self.USER_2)
+                output_3 = self._memoiseme(self.USER_1)
+
+        self.assertIsNot(output_1, output_2)
+        self.assertIs(output_1, output_3)
+
+    def test_memoisation_clears_outside_batches(self):
+        with BatchController.batch(self.USER_1):
+            output_1 = self._memoiseme(self.USER_1)
+
+        with BatchController.batch(self.USER_1):
+            output_2 = self._memoiseme(self.USER_1)
+
+        self.assertIsNot(output_1, output_2)
+
+    @classmethod
+    @BatchController.memoise
+    def _memoiseme(self, user):
+        return object()
+
+    def test_batch_end_functionality_is_called(self):
+        class Ender(object):
+            end_count = 0
+            def end_batch(self):
+                self.end_count += 1
+
+        @BatchController.memoise
+        def get_ender(user):
+            return Ender()
+
+        # end_batch should get called once on exiting the batch
+        with BatchController.batch(self.USER_1):
+            ender = get_ender(self.USER_1)
+        self.assertEquals(1, ender.end_count)
+
+        # end_batch should get called once on exiting the batch
+        # no matter how deep the object gets cached
+        with BatchController.batch(self.USER_1):
+            with BatchController.batch(self.USER_1):
+                ender = get_ender(self.USER_1)
+        self.assertEquals(1, ender.end_count)

registrasion/tests/test_cart.py

@@ -12,6 +12,7 @@ from registrasion.models import commerce
 from registrasion.models import conditions
 from registrasion.models import inventory
 from registrasion.models import people
+from registrasion.controllers.batch import BatchController
 from registrasion.controllers.product import ProductController
 
 from controller_helpers import TestingCartController
@@ -360,3 +361,65 @@ class BasicCartTests(RegistrationCartTestCase):
 
     def test_available_products_respects_product_limits(self):
         self.__available_products_test(self.PROD_4, 6)
+
+    def test_cart_controller_for_user_is_memoised(self):
+        # - that for_user is memoised
+        with BatchController.batch(self.USER_1):
+            cart = TestingCartController.for_user(self.USER_1)
+            cart_2 = TestingCartController.for_user(self.USER_1)
+        self.assertIs(cart, cart_2)
+
+    def test_cart_revision_does_not_increment_if_not_modified(self):
+        cart = TestingCartController.for_user(self.USER_1)
+        rev_0 = cart.cart.revision
+
+        with BatchController.batch(self.USER_1):
+            # Memoise the cart
+            same_cart = TestingCartController.for_user(self.USER_1)
+            # Do nothing on exit
+        
+        rev_1 = self.reget(cart.cart).revision
+        self.assertEqual(rev_0, rev_1)
+
+    def test_cart_revision_only_increments_at_end_of_batches(self):
+        cart = TestingCartController.for_user(self.USER_1)
+        rev_0 = cart.cart.revision
+
+        with BatchController.batch(self.USER_1):
+            # Memoise the cart
+            same_cart = TestingCartController.for_user(self.USER_1)
+            same_cart.add_to_cart(self.PROD_1, 1)
+            rev_1 = self.reget(same_cart.cart).revision
+
+        rev_2 = self.reget(cart.cart).revision
+
+        self.assertEqual(rev_0, rev_1)
+        self.assertNotEqual(rev_0, rev_2)
+
+    def test_cart_discounts_only_calculated_at_end_of_batches(self):
+        def count_discounts(cart):
+            return cart.cart.discountitem_set.count()
+
+        cart = TestingCartController.for_user(self.USER_1)
+        self.make_discount_ceiling("FLOOZLE")
+        count_0 = count_discounts(cart)
+
+        with BatchController.batch(self.USER_1):
+            # Memoise the cart
+            same_cart = TestingCartController.for_user(self.USER_1)
+
+            with BatchController.batch(self.USER_1):
+                # Memoise the cart
+                same_cart_2 = TestingCartController.for_user(self.USER_1)
+
+                same_cart_2.add_to_cart(self.PROD_1, 1)
+                count_1 = count_discounts(same_cart_2)
+
+            count_2 = count_discounts(same_cart)
+
+        count_3 = count_discounts(cart)
+
+        self.assertEqual(0, count_0)
+        self.assertEqual(0, count_1)
+        self.assertEqual(0, count_2)
+        self.assertEqual(1, count_3)

registrasion/views.py

@@ -5,9 +5,10 @@ from registrasion import util
 from registrasion.models import commerce
 from registrasion.models import inventory
 from registrasion.models import people
-from registrasion.controllers.discount import DiscountController
+from registrasion.controllers.batch import BatchController
 from registrasion.controllers.cart import CartController
 from registrasion.controllers.credit_note import CreditNoteController
+from registrasion.controllers.discount import DiscountController
 from registrasion.controllers.invoice import InvoiceController
 from registrasion.controllers.product import ProductController
 from registrasion.exceptions import CartValidationError
@@ -170,6 +171,7 @@ def guided_registration(request):
             category__in=cats,
         ).select_related("category")
 
+        with BatchController.batch(request.user):
             available_products = set(ProductController.available_products(
                 request.user,
                 products=all_products,
@@ -181,7 +183,6 @@ def guided_registration(request):
                 attendee.save()
                 return next_step
 
-        with CartController.operations_batch(request.user):
             for category in cats:
                 products = [
                     i for i in available_products
@@ -345,6 +346,7 @@ def product_category(request, category_id):
     category_id = int(category_id)  # Routing is [0-9]+
     category = inventory.Category.objects.get(pk=category_id)
 
+    with BatchController.batch(request.user):
         products = ProductController.available_products(
             request.user,
             category=category,