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| -rw-r--r-- | docs/ref/models/expressions.txt | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/docs/ref/models/expressions.txt b/docs/ref/models/expressions.txt index 7a1945a948..4eb16e361f 100644 --- a/docs/ref/models/expressions.txt +++ b/docs/ref/models/expressions.txt @@ -174,6 +174,22 @@ robust: it will only ever update the field based on the value of the field in the database when the :meth:`~Model.save()` or ``update()`` is executed, rather than based on its value when the instance was retrieved. +``F()`` assignments persist after ``Model.save()`` +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +``F()`` objects assigned to model fields persist after saving the model +instance and will be applied on each :meth:`~Model.save()`. For example:: + + reporter = Reporters.objects.get(name='Tintin') + reporter.stories_filed = F('stories_filed') + 1 + reporter.save() + + reporter.name = 'Tintin Jr.' + reporter.save() + +``stories_filed`` will be updated twice in this case. If it's initially ``1``, +the final value will be ``3``. + Using ``F()`` in filters ~~~~~~~~~~~~~~~~~~~~~~~~ |