[soc2010/query-refactor] Cleaned up implementation of negation in MongoDB, and no longer rely on a feature from MongoDB unstable version.

git-svn-id: http://code.djangoproject.com/svn/django/branches/soc2010/query-refactor@13368 bcc190cf-cafb-0310-a4f2-bffc1f526a37

2 files changed, 10 insertions, 2 deletions

diff --git a/django/db/models/sql/query.py b/django/db/models/sql/query.py
index 959990f628..6836337429 100644
--- a/django/db/models/sql/query.py
+++ b/django/db/models/sql/query.py
@@ -1077,7 +1077,11 @@ class Query(object):
                     # it's short-circuited in the Where class.
                     # We also need to handle the case where a subquery is provided
                     entry = self.where_class()
-                    entry.add((Constraint(alias, col, None), 'isnull', True), AND)
+                    entry.add((
+                        Constraint(alias, col, None, eliminatable_if=lambda connection: not getattr(connection.features, "sql_nulls", True)),
+                        'isnull',
+                        True
+                    ), AND)
                     entry.negate()
                     self.where.add(entry, AND)
 
diff --git a/django/db/models/sql/where.py b/django/db/models/sql/where.py
index 4e5a647259..e953bca703 100644
--- a/django/db/models/sql/where.py
+++ b/django/db/models/sql/where.py
@@ -267,8 +267,9 @@ class Constraint(object):
     An object that can be passed to WhereNode.add() and knows how to
     pre-process itself prior to including in the WhereNode.
     """
-    def __init__(self, alias, col, field):
+    def __init__(self, alias, col, field, eliminatable_if=None):
         self.alias, self.col, self.field = alias, col, field
+        self.elimintable_if = eliminatable_if
 
     def __getstate__(self):
         """Save the state of the Constraint for pickling.
@@ -321,6 +322,9 @@ class Constraint(object):
         except ObjectDoesNotExist:
             raise EmptyShortCircuit
 
+        if self.elimintable_if and self.elimintable_if(connection):
+            raise FullResultSet
+
         return (self.alias, self.col, db_type), params
 
     def relabel_aliases(self, change_map):