#13105: [patch] get or create thread safety
---------------------------------------------------+------------------------
Reporter: toplex | Owner: toplex
Status: closed | Milestone:
Component: Database layer (models, ORM) | Version: 1.1
Resolution: duplicate | Keywords:
thread;multithread;relation;get_or_create
Stage: Unreviewed | Has_patch: 1
Needs_docs: 0 | Needs_tests: 0
Needs_better_patch: 0 |
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Changes (by kmtracey):
* status: new => closed
* needs_better_patch: => 0
* resolution: => duplicate
* needs_tests: => 0
* needs_docs: => 0
Comment:
For the regular model `get_or_create`, you won't get duplicates if you
have specified the unique constraints on your model/database properly. The
routine is coded to rely on the database raising an !IntegrityError for
duplicates. I assume the same is true for adding relations, though I have
not looked closely at that case. If there is a problem for the relation-
adding case, when they are defined to Django as unique, then that needs to
be spelled out in detail with example models and showing how duplicates
can arise.
I don't believe adding a 'fix' for the case where database unique
constraints have not be set properly, that only works for multi-thread but
not multi-process situations, will help here. We've already got #12759
open for better documentation on get_or_create and the situations where it
can be used.
In general we would not add a fix for a multi-process/multi-thread problem
that only addresses one of the two environments. In the case of
`get_or_create`, we push the responsibility off to the database, which
already has to deal with it.
Also, for the future, patches need to be against trunk, not an existing
release (see http://docs.djangoproject.com/en/dev/internals/contributing
/#patch-style). The code touched in the patch has changed considerably
since 1.1.1. First priority for bug fixes is trunk, and then fixes are
backported to the latest release branch. Thus a patch against an old
release doesn't help much.
--
Ticket URL: <http://code.djangoproject.com/ticket/13105#comment:1>
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