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Fixed #28273 -- Doc'd fast nullable column creation with defaults.

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Caio Ariede 2019-10-04 10:55:41 -03:00 committed by Mariusz Felisiak
parent e3f647f4d5
commit 06909fe084
1 changed files with 15 additions and 0 deletions
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docs/ref/migration-operations.txt
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@ -150,6 +150,21 @@ a default value to put into existing rows. It does not affect the behavior
of setting defaults in the database directly - Django never sets database of setting defaults in the database directly - Django never sets database
defaults and always applies them in the Django ORM code. defaults and always applies them in the Django ORM code.
.. warning::
On older databases, adding a field with a default value may cause a full
rewrite of the table. This happens even for nullable fields and may have a
negative performance impact. To avoid that, the following steps should be
taken.
* Add the nullable field without the default value and run the
:djadmin:`makemigrations` command. This should generate a migration with
an ``AddField`` operation.
* Add the default value to your field and run the :djadmin:`makemigrations`
command. This should generate a migration with an ``AlterField``
operation.
``RemoveField`` ``RemoveField``
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