#9205: Add savepoint protection to Model.save()
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Reporter: Richard Davies <[EMAIL PROTECTED]> | Owner: nobody
Status: new | Milestone:
Component: Database layer (models, ORM) | Version:
SVN
Keywords: | Stage:
Unreviewed
Has_patch: 1 |
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[8314] introduced savepoints - these are a no-op for all databases except
for Postgresql, on which they must be used to continue using a database
connection after an IntegrityError.
IntegrityError can be raised in save() in several cases:
* because of a conflict on a unique field (example below)
* when using force_insert or force_update if this is not possible
* if there is a race between when save() decides whether to insert/update
and when it actually does so
At present, the user should wrap calls to save() with savepoints if they
are likely to fail for any of these reasons.
This patch changes save() to always wrap the call to save_base() in
savepoints, meaning that all of the above cases leave a working database
connection and the user does not need to wrap. It means that "user" code
wrapping save() can be removed from several places in Django and its test
suite. The complete test suite still passes on Postgresql.
Possibly the savepoints should move _inside_ save_base(), so that direct
calls also benefit from them. Doing this naively leads to extra test suite
failures, which I have not investigated.
On performance: we are now making many more savepoint calls, which could
have performance implications. These calls are no-ops on non-Postgresql
backends, so should have little impact there. On Postgresql, time to run
the complete test suite was unchanged on my development machine. So, I
conclude that there are no performance implications.
--------------------------
Example of IntegrityError from unique field conflict:
{{{
I have a simple model:
================
class Test(models.Model):
data1 = models.IntegerField(unique=True)
data2 = models.IntegerField()
================
and a view using it:
================
def render(request):
a = Test()
a.data1 = 1
a.data2 = 10
a.save()
b = Test()
b.data1 = 1
b.data2 = 20
try:
b.save()
except IntegrityError:
# Expected since data1 not unique
# savepoint protection needed here for postgresql today
pass
c = Test()
c.data1 = 2
c.data2 = 30
# Today: c is saved by most database backends, but not by postgresql.
# savepoint protection would be needed above for postgresql.
#
# With patch: c is saved by all database backends.
c.save()
return HttpResponse('Test')
}}}
--
Ticket URL: <http://code.djangoproject.com/ticket/9205>
Django <http://code.djangoproject.com/>
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