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/query.py

@@ -2,20 +2,13 @@
 The main QuerySet implementation. This provides the public API for the ORM.
 """
 
-try:
-    set
-except NameError:
-    from sets import Set as set     # Python 2.3 fallback
-
 from copy import deepcopy
-
 from django.db import connection, transaction, IntegrityError
 from django.db.models.aggregates import Aggregate
 from django.db.models.fields import DateField
 from django.db.models.query_utils import Q, select_related_descend, CollectedObjects, CyclicDependency, deferred_class_factory
 from django.db.models import signals, sql
 
-
 # Used to control how many objects are worked with at once in some cases (e.g.
 # when deleting objects).
 CHUNK_SIZE = 100
@@ -444,6 +437,11 @@ class QuerySet(object):
         return query.execute_sql(None)
     _update.alters_data = True
 
+    def exists(self):
+        if self._result_cache is None:
+            return self.query.has_results()
+        return bool(self._result_cache)
+
     ##################################################
     # PUBLIC METHODS THAT RETURN A QUERYSET SUBCLASS #
     ##################################################