Fixed #11402: added a QuerySet.exists() method. Thanks, Alex Gaynor.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@11646 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/sql/query.py

@@ -8,7 +8,6 @@ all about the internals of models in order to get the information it needs.
 """
 
 from copy import deepcopy
-
 from django.utils.tree import Node
 from django.utils.datastructures import SortedDict
 from django.utils.encoding import force_unicode
@@ -24,11 +23,6 @@ from django.core.exceptions import FieldError
 from datastructures import EmptyResultSet, Empty, MultiJoin
 from constants import *
 
-try:
-    set
-except NameError:
-    from sets import Set as set     # Python 2.3 fallback
-
 __all__ = ['Query', 'BaseQuery']
 
 class BaseQuery(object):
@@ -384,6 +378,15 @@ class BaseQuery(object):
 
         return number
 
+    def has_results(self):
+        q = self.clone()
+        q.add_extra({'a': 1}, None, None, None, None, None)
+        q.add_fields(())
+        q.set_extra_mask(('a',))
+        q.set_aggregate_mask(())
+        q.clear_ordering()
+        return bool(q.execute_sql())
+
     def as_sql(self, with_limits=True, with_col_aliases=False):
         """
         Creates the SQL for this query. Returns the SQL string and list of