Ensure a Bankcard's type isn't lost after saving

Before this change, the type of a bankcard would be clobbered by saving
and reloading.

Fixes #1486, #1487

oscar/apps/payment/abstract_models.py

         self.issue_number = kwargs.pop('issue_number', None)
         self.ccv = kwargs.pop('ccv', None)
         super(AbstractBankcard, self).__init__(*args, **kwargs)
-        self.card_type = bankcards.bankcard_type(self.number)
-        if self.card_type is None:
-            self.card_type = 'Unknown card type'
+
+        # Initialise the card-type
+        if self.id is None:
+            self.card_type = bankcards.bankcard_type(self.number)
+            if self.card_type is None:
+                self.card_type = 'Unknown card type'
 
     class Meta:
         abstract = True

tests/integration/payment/model_tests.py

 from decimal import Decimal as D
+import datetime
 
 from django.test import TestCase
 from django_dynamic_fixture import G
 
 from oscar.test import factories
 from oscar.apps.payment import models
+from oscar.apps.payment.models import Bankcard
 
 
 class TestAPaymentSource(TestCase):
         self.source.allocate(D('100.00'))
         self.source.debit(D('80.00'))
         self.source.refund(D('50.00'))
+
+
+class TestBankcard(TestCase):
+
+    def test_cardtype_persists_after_save(self):
+        user = factories.UserFactory()
+        end = datetime.date(day=1, month=1, year=2010)
+        bankcard = Bankcard(
+            user=user, number="5500000000000004", expiry_date=end)
+        self.assertEqual('Mastercard', bankcard.card_type)
+
+        bankcard.save()
+        self.assertEqual('Mastercard', bankcard.card_type)
+
+        reloaded_bankcard = Bankcard.objects.get(id=bankcard.id)
+        self.assertEqual('Mastercard', reloaded_bankcard.card_type)

tests/unit/payment/model_tests.py

 
 from django.test import TestCase
 
+from oscar.core.compat import get_user_model
 from oscar.apps.payment.models import Bankcard, Source
 
 
         bankcard = Bankcard(expiry_date=end)
         self.assertEqual("01/10", bankcard.expiry_month())
 
+    def test_bankcard_card_correct_save(self):
+        # issue #1486
+        user_klass = get_user_model()
+        user = user_klass.objects.create_user('_', 'a@a.com', 'pwd')
+        end = datetime.date(day=1, month=1, year=2010)
+        bankcard = Bankcard.objects.create(
+            user=user, number="5500000000000004", expiry_date=end)
+        saved_bankcard = Bankcard.objects.get(id=bankcard.id)
+        self.assertEqual('Mastercard', saved_bankcard.card_type)
+
 
 class TestSource(TestCase):