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Fixed #29313 -- Doc'd how to use F() to sort null values.

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drd0013 2018-04-19 17:07:40 -07:00 committed by Tim Graham
parent 534d8d875e
commit 5d923f2d8c
1 changed files with 17 additions and 0 deletions
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docs/ref/models/expressions.txt
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@ -228,6 +228,21 @@ primary key value rather than a model instance::
>> car.built_by >> car.built_by
3 3
.. _using-f-to-sort-null-values:
Using ``F()`` to sort null values
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Use ``F()`` and the ``nulls_first`` or ``nulls_last`` keyword argument to
:meth:`.Expression.asc` or :meth:`~.Expression.desc` to control the ordering of
a field's null values. By default, the ordering depends on your database.
For example, to sort companies that haven't been contacted (``last_contacted``
is null) after companies that have been contacted::
from django.db.models import F
Company.object.order_by(F('last_contacted').desc(nulls_last=True))
.. _func-expressions: .. _func-expressions:
``Func()`` expressions ``Func()`` expressions
@ -971,12 +986,14 @@ calling the appropriate methods on the wrapped expression.
Returns the expression ready to be sorted in ascending order. Returns the expression ready to be sorted in ascending order.
``nulls_first`` and ``nulls_last`` define how null values are sorted. ``nulls_first`` and ``nulls_last`` define how null values are sorted.
See :ref:`using-f-to-sort-null-values` for example usage.
.. method:: desc(nulls_first=False, nulls_last=False) .. method:: desc(nulls_first=False, nulls_last=False)
Returns the expression ready to be sorted in descending order. Returns the expression ready to be sorted in descending order.
``nulls_first`` and ``nulls_last`` define how null values are sorted. ``nulls_first`` and ``nulls_last`` define how null values are sorted.
See :ref:`using-f-to-sort-null-values` for example usage.
.. method:: reverse_ordering() .. method:: reverse_ordering()