From: Mike Bayer <mike_mp@zzzcomputing.com>
Date: Wed, 24 Sep 2014 18:49:30 +0000 (-0400)
Subject: - clarify documentation on exists() that it is preferred to be in the
X-Git-Tag: rel_0_9_8~17
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=98f457a5e2f8b9ec9f13a575fc99eca2ef1fc310;p=thirdparty%2Fsqlalchemy%2Fsqlalchemy.git

- clarify documentation on exists() that it is preferred to be in the
WHERE clause.  fixes #3212
---

diff --git a/lib/sqlalchemy/orm/query.py b/lib/sqlalchemy/orm/query.py
index a9ed4d4e71..80d4d0cdd8 100644
--- a/lib/sqlalchemy/orm/query.py
+++ b/lib/sqlalchemy/orm/query.py
@@ -2574,6 +2574,19 @@ class Query(object):
                 SELECT 1 FROM users WHERE users.name = :name_1
             ) AS anon_1
 
+        The EXISTS construct is usually used in the WHERE clause::
+
+            session.query(User.id).filter(q.exists()).scalar()
+
+        Note that some databases such as SQL Server don't allow an
+        EXISTS expression to be present in the columns clause of a
+        SELECT.    To select a simple boolean value based on the exists
+        as a WHERE, use :func:`.literal`::
+
+            from sqlalchemy import literal
+
+            session.query(literal(True)).filter(q.exists()).scalar()
+
         .. versionadded:: 0.8.1
 
         """