Minor optimisation to ACLs (use .exists() instead of bool() because it's…

Minor optimisation to ACLs (use .exists() instead of bool() because it's faster), fix an issue on Django 1.5 where EmptyQuerySet has no method select_related_common()

wiki/models/article.py

@@ -57,7 +57,7 @@ class Article(models.Model):
         if user == self.owner:
             return True
         if self.group_read:
-            if self.group and user.groups.filter(id=self.group.id):
+            if self.group and user.groups.filter(id=self.group.id).exists():
                 return True
         if self.can_moderate(user):
             return True
@@ -74,7 +74,7 @@ class Article(models.Model):
         if user == self.owner:
             return True
         if self.group_write:
-            if self.group and user and user.groups.filter(id=self.group.id):
+            if self.group and user and user.groups.filter(id=self.group.id).exists():
                 return True
         if self.can_moderate(user):
             return True

wiki/models/urlpath.py

@@ -60,6 +60,8 @@ class URLPath(MPTTModel):
         If the cached ancestors were not set explicitly, they will be retrieved from
         the database.
         """
+        if not self.get_ancestors().exists():
+            self._cached_ancestors = []
         if not hasattr(self, "_cached_ancestors"):
             self._cached_ancestors = list(self.get_ancestors().select_related_common() )