Adds an operations_batch context manager that allows batches of modifying operations to be nested. Closes #44.

registrasion/controllers/cart.py

@@ -1,4 +1,5 @@
 import collections
+import contextlib
 import datetime
 import functools
 import itertools
@@ -23,11 +24,18 @@ from .product import ProductController
 
 def _modifies_cart(func):
     ''' Decorator that makes the wrapped function raise ValidationError
-    if we're doing something that could modify the cart. '''
+    if we're doing something that could modify the cart.
+
+    It also wraps the execution of this function in a database transaction,
+    and marks the boundaries of a cart operations batch.
+    '''
 
     @functools.wraps(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:
+                mark.mark = True  # Marker that we've modified the cart
                 return func(self, *a, **k)
 
     return inner
@@ -56,13 +64,57 @@ class CartController(object):
             )
         return cls(existing)
 
+
+    # Marks the carts that are currently in batches
+    _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.
+        '''
+
+        ctrl = cls.for_user(user)
+        _id = ctrl.cart.id
+
+        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
+            if modified and cls._BATCH_COUNT[_id] == 0 and success:
+                ctrl._end_batch()
+                cls._MODIFIED_CARTS.remove(_id)
+
     def _fail_if_cart_is_not_active(self):
         self.cart.refresh_from_db()
         if self.cart.status != commerce.Cart.STATUS_ACTIVE:
             raise ValidationError("You can only amend active carts.")
 
-    @_modifies_cart
-    def extend_reservation(self):
+    def _autoextend_reservation(self):
         ''' Updates the cart's time last updated value, which is used to
         determine whether the cart has reserved the items and discounts it
         holds. '''
@@ -84,21 +136,26 @@ class CartController(object):
         self.cart.time_last_updated = timezone.now()
         self.cart.reservation_duration = max(reservations)
 
-    @_modifies_cart
-    def end_batch(self):
+    def _end_batch(self):
         ''' Performs operations that occur occur at the end of a batch of
         product changes/voucher applications etc.
-        THIS SHOULD BE PRIVATE
+
+        You need to call this after you've finished modifying the user's cart.
+        This is normally done by wrapping a block of code using
+        ``operations_batch``.
+
         '''
 
-        self.recalculate_discounts()
 
-        self.extend_reservation()
+        self.cart.refresh_from_db()
+
+        self._recalculate_discounts()
+
+        self._autoextend_reservation()
         self.cart.revision += 1
         self.cart.save()
 
     @_modifies_cart
-    @transaction.atomic
     def set_quantities(self, product_quantities):
         ''' Sets the quantities on each of the products on each of the
         products specified. Raises an exception (ValidationError) if a limit
@@ -140,8 +197,6 @@ class CartController(object):
 
         items_in_cart.filter(quantity=0).delete()
 
-        self.end_batch()
-
     def _test_limits(self, product_quantities):
         ''' Tests that the quantity changes we intend to make do not violate
         the limits and flag conditions imposed on the products. '''
@@ -213,7 +268,6 @@ class CartController(object):
 
         # If successful...
         self.cart.vouchers.add(voucher)
-        self.end_batch()
 
     def _test_voucher(self, voucher):
         ''' Tests whether this voucher is allowed to be applied to this cart.
@@ -331,7 +385,6 @@ class CartController(object):
             raise ValidationError(errors)
 
     @_modifies_cart
-    @transaction.atomic
     def fix_simple_errors(self):
         ''' This attempts to fix the easy errors raised by ValidationError.
         This includes removing items from the cart that are no longer
@@ -363,11 +416,9 @@ class CartController(object):
 
         self.set_quantities(zeros)
 
-    @_modifies_cart
     @transaction.atomic
-    def recalculate_discounts(self):
-        ''' Calculates all of the discounts available for this product.
-        '''
+    def _recalculate_discounts(self):
+        ''' Calculates all of the discounts available for this product.'''
 
         # Delete the existing entries.
         commerce.DiscountItem.objects.filter(cart=self.cart).delete()

registrasion/controllers/invoice.py

@@ -29,6 +29,7 @@ class InvoiceController(ForId, object):
         If such an invoice does not exist, the cart is validated, and if valid,
         an invoice is generated.'''
 
+        cart.refresh_from_db()
         try:
             invoice = commerce.Invoice.objects.exclude(
                 status=commerce.Invoice.STATUS_VOID,
@@ -74,6 +75,8 @@ class InvoiceController(ForId, object):
     def _generate(cls, cart):
         ''' Generates an invoice for the given cart. '''
 
+        cart.refresh_from_db()
+
         issued = timezone.now()
         reservation_limit = cart.reservation_duration + cart.time_last_updated
         # Never generate a due time that is before the issue time
@@ -251,6 +254,9 @@ class InvoiceController(ForId, object):
     def _invoice_matches_cart(self):
         ''' Returns true if there is no cart, or if the revision of this
         invoice matches the current revision of the cart. '''
+
+        self._refresh()
+
         cart = self.invoice.cart
         if not cart:
             return True