From: Mike Bayer <mike_mp@zzzcomputing.com>
Date: Sun, 7 Feb 2010 00:18:15 +0000 (+0000)
Subject: add a note about type for ColumnElement
X-Git-Tag: rel_0_6beta2~223
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=54df3ee2ab1052533f49e596d902d597eb140c52;p=thirdparty%2Fsqlalchemy%2Fsqlalchemy.git

add a note about type for ColumnElement
---

diff --git a/lib/sqlalchemy/ext/compiler.py b/lib/sqlalchemy/ext/compiler.py
index 56502bd28f..7861096f9e 100644
--- a/lib/sqlalchemy/ext/compiler.py
+++ b/lib/sqlalchemy/ext/compiler.py
@@ -131,6 +131,14 @@ A big part of using the compiler extension is subclassing SQLAlchemy expression
   "column-like" elements. Anything that you'd place in the "columns" clause of
   a SELECT statement (as well as order by and group by) can derive from this -
   the object will automatically have Python "comparison" behavior.
+  
+  :class:`~sqlalchemy.sql.expression.ColumnElement` classes want to have a
+  ``type`` member which is expression's return type.  This can be established
+  at the instance level in the constructor, or at the class level if its
+  generally constant::
+  
+      class timestamp(ColumnElement):
+          type = TIMESTAMP()
  
 * :class:`~sqlalchemy.sql.expression.FunctionElement` - This is a hybrid of a
   ``ColumnElement`` and a "from clause" like object, and represents a SQL