magic-removal: Modified descriptor to return None rather than raising DoesNotExist if null=True for a related field.

git-svn-id: http://code.djangoproject.com/svn/django/branches/magic-removal@2511 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/fields/related.py

@@ -117,6 +117,9 @@ class ReverseSingleRelatedObjectDescriptor(object):
         except AttributeError:
             val = getattr(instance, self.field.attname)
             if val is None:
+                # If Null is an allowed value, return it.
+                if self.field.null:
+                    return None
                 raise self.field.rel.to.DoesNotExist
             other_field = self.field.rel.get_related_field()
             if other_field.rel:

tests/modeltests/m2o_recursive/models.py

@@ -30,10 +30,8 @@ API_TESTS = """
 [Child category]
 >>> r.child_set.get(name__startswith='Child')
 Child category
->>> r.parent
-Traceback (most recent call last):
-    ...
-DoesNotExist
+>>> print r.parent
+None
 
 >>> c.child_set.all()
 []

tests/modeltests/many_to_one_null/models.py

@@ -61,23 +61,20 @@ Second
 >>> a3.save()
 >>> a3.id
 3
->>> a3.reporter
-Traceback (most recent call last):
-    ...
-DoesNotExist
+>>> print a3.reporter
+None
 
+# Need to reget a3 to refresh the cache
 >>> a3 = Article.objects.get(pk=3)
 >>> print a3.reporter.id
 Traceback (most recent call last):
     ...
-DoesNotExist
+AttributeError: 'NoneType' object has no attribute 'id'
 
-# Accessing an article's 'reporter' attribute throws ReporterDoesNotExist
+# Accessing an article's 'reporter' attribute returns None
 # if the reporter is set to None.
->>> a3.reporter
-Traceback (most recent call last):
-    ...
-DoesNotExist
+>>> print a3.reporter
+None
 
 # To retrieve the articles with no reporters set, use "reporter__isnull=True".
 >>> Article.objects.filter(reporter__isnull=True)