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[1.8.x] Fixed #24486 -- Documented method to provide output_field to mixed F expressions 

Backport of 820381d38b from master
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Josh Smeaton 2015-03-16 16:11:03 +11:00 committed by Tim Graham
parent 63b998a653
commit 09062e9509
1 changed files with 11 additions and 0 deletions
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docs/ref/models/expressions.txt
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@ -278,6 +278,17 @@ should define the desired ``output_field``. For example, adding an
``IntegerField()`` and a ``FloatField()`` together should probably have ``IntegerField()`` and a ``FloatField()`` together should probably have
``output_field=FloatField()`` defined. ``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 .. versionchanged:: 1.8
``output_field`` is a new parameter. ``output_field`` is a new parameter.