Credit change is now atomic

cash/models.py

@@ -1,4 +1,3 @@
-
 from django.conf import settings
 from django.db import models
 from django.core.files import File
@@ -9,6 +8,7 @@ from django.dispatch import receiver
 from django_auth_ldap.backend import populate_user
 from django.utils.translation import ugettext_lazy as _
 from django.utils.translation import ugettext_noop
+from django.db import transaction
 import PIL
 import StringIO
 
@@ -43,13 +43,16 @@ class Account(models.Model):
 				    instance.ldap_user.attrs['employeenumber'][0]
 				instance.account.save()
 
+	@transaction.atomic
 	def change_credit(self, amount, subject, desc):
-		self.credit += amount
+		# For atomicity fetch current value first
+		cur = Account.objects.filter(pk=self.pk)[0]
+		self.credit = cur.credit + amount
 		self.save()
 
-		transaction = Transaction(account=self, subject=subject,
-								  amount=amount, description=desc)
-		transaction.save()
+		trans = Transaction(account=self, subject=subject,
+						    amount=amount, description=desc)
+		trans.save()
 
 	def buy_products(self, products):
 		# TODO place it somewhere else