Nested query support.

This extends previous functionality that allowed passing Query objects as the
rvals to filters. You can now pass QuerySets, which requires less poking at
opaque attributes. See the documentation of the "__in" lookup type for the
details.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@9701 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/query.py

@@ -641,6 +641,15 @@ class QuerySet(object):
         """
         pass
 
+    def as_sql(self):
+        """
+        Returns the internal query's SQL and parameters (as a tuple).
+
+        This is a private (internal) method. The name is chosen to provide
+        uniformity with other interfaces (in particular, the Query class).
+        """
+        obj = self.values("pk")
+        return obj.query.as_nested_sql()
 
 class ValuesQuerySet(QuerySet):
     def __init__(self, *args, **kwargs):