From: Mike Bayer <mike_mp@zzzcomputing.com>
Date: Wed, 22 Jun 2011 21:18:41 +0000 (-0400)
Subject: - add doc example for column_property() on an association table per [ticket:1481]
X-Git-Tag: rel_0_7_2~55
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=670b640c88d0dab31a0f4c9a9096e69b371bdd62;p=thirdparty%2Fsqlalchemy%2Fsqlalchemy.git

- add doc example for column_property() on an association table per [ticket:1481]
---

diff --git a/doc/build/orm/mapper_config.rst b/doc/build/orm/mapper_config.rst
index 259a6ecbab..d69cff6426 100644
--- a/doc/build/orm/mapper_config.rst
+++ b/doc/build/orm/mapper_config.rst
@@ -296,7 +296,22 @@ Correlated subqueries may be used as well::
             )
     })
 
-The declarative form of the above is described in :ref:`declarative_sql_expressions`.
+For many-to-many relationships, use :func:`.and_` to join the fields of the
+association table to both tables in a relation::
+
+    from sqlalchemy import and_
+
+    mapper(Author, authors, properties={
+        'book_count': column_property(
+                            select([func.count(books.c.id)], 
+                                and_(
+                                    book_authors.c.author_id==authors.c.id,
+                                    book_authors.c.book_id==books.c.id
+                                )))
+        })
+
+For examples of :func:`.column_property` using Declarative, see 
+:ref:`declarative_sql_expressions`.
 
 Note that :func:`.column_property` is used to provide the effect of a SQL
 expression that is actively rendered into the SELECT generated for a