mirror of https://github.com/django/django.git
0701bb8e1f
Models that use SET, SET_NULL, and SET_DEFAULT as on_delete handler don't have to fetch objects for the sole purpose of passing them back to a follow up UPDATE query filtered by the retrieved objects primary key. This was achieved by flagging SET handlers as _lazy_ and having the collector logic defer object collections until the last minute. This should ensure that the rare cases where custom on_delete handlers are defined remain uncalled when when dealing with an empty collection of instances. This reduces the number queries required to apply SET handlers from 2 to 1 where the remaining UPDATE use the same predicate as the non removed SELECT query. In a lot of ways this is similar to the fast-delete optimization that was added in #18676 but for updates this time. The conditions only happen to be simpler in this case because SET handlers are always terminal. They never cascade to more deletes that can be combined. Thanks Renan GEHAN for the report. |
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README.rst
====== Django ====== Django is a high-level Python web framework that encourages rapid development and clean, pragmatic design. Thanks for checking it out. All documentation is in the "``docs``" directory and online at https://docs.djangoproject.com/en/stable/. If you're just getting started, here's how we recommend you read the docs: * First, read ``docs/intro/install.txt`` for instructions on installing Django. * Next, work through the tutorials in order (``docs/intro/tutorial01.txt``, ``docs/intro/tutorial02.txt``, etc.). * If you want to set up an actual deployment server, read ``docs/howto/deployment/index.txt`` for instructions. * You'll probably want to read through the topical guides (in ``docs/topics``) next; from there you can jump to the HOWTOs (in ``docs/howto``) for specific problems, and check out the reference (``docs/ref``) for gory details. * See ``docs/README`` for instructions on building an HTML version of the docs. Docs are updated rigorously. If you find any problems in the docs, or think they should be clarified in any way, please take 30 seconds to fill out a ticket here: https://code.djangoproject.com/newticket To get more help: * Join the ``#django`` channel on ``irc.libera.chat``. Lots of helpful people hang out there. See https://web.libera.chat if you're new to IRC. * Join the django-users mailing list, or read the archives, at https://groups.google.com/group/django-users. To contribute to Django: * Check out https://docs.djangoproject.com/en/dev/internals/contributing/ for information about getting involved. To run Django's test suite: * Follow the instructions in the "Unit tests" section of ``docs/internals/contributing/writing-code/unit-tests.txt``, published online at https://docs.djangoproject.com/en/dev/internals/contributing/writing-code/unit-tests/#running-the-unit-tests Supporting the Development of Django ==================================== Django's development depends on your contributions. If you depend on Django, remember to support the Django Software Foundation: https://www.djangoproject.com/fundraising/