From 09062e9509c56088793776bfda9db056c797552e Mon Sep 17 00:00:00 2001
From: Josh Smeaton <josh.smeaton@gmail.com>
Date: Mon, 16 Mar 2015 16:11:03 +1100
Subject: [PATCH] [1.8.x] Fixed #24486 -- Documented method to provide
 output_field to mixed F expressions

Backport of 820381d38bc02ea8b92837ce869e7332a7db9913 from master
---
 docs/ref/models/expressions.txt | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/docs/ref/models/expressions.txt b/docs/ref/models/expressions.txt
index 0224a21e54..ef319d5d10 100644
--- a/docs/ref/models/expressions.txt
+++ b/docs/ref/models/expressions.txt
@@ -278,6 +278,17 @@ should define the desired ``output_field``. For example, adding an
 ``IntegerField()`` and a ``FloatField()`` together should probably have
 ``output_field=FloatField()`` defined.
 
+.. note::
+
+    When you need to define the ``output_field`` for ``F`` expression
+    arithmetic between different types, it's necessary to surround the
+    expression in another expression::
+
+        from django.db.models import DateTimeField, ExpressionNode, F
+
+        Race.objects.annotate(finish=ExpressionNode(
+            F('start') + F('duration'), output_field=DateTimeField()))
+
 .. versionchanged:: 1.8
 
     ``output_field`` is a new parameter.