#26552: `TransactionTestCase.serialized_rollback` fails to restore objects due
to
ordering constraints
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Reporter: Aymeric Augustin | Owner: nobody
Type: Bug | Status: new
Component: Testing framework | Version: 1.9
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 1 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by Matthijs Kooijman):
I've run into a problem related to this one (just reported as #31051), so
I ended up looking into this problem as well. The original report still
seems accurate to me, with the proposed solution valid.
I've been working on a fix and (most of the work), testcase for this
problem. I'll do some more testing and provide a proper PR for this issue
and #31051 soon. The testcase is not ideal yet (testing the testing
framework is tricky), but I'll expand on that in the PR.
Furthermore, I noticed that `loaddata` does not just wrap everything in a
transaction, it also explicitly disables constraint checks inside the
transaction:
{{{
with connection.constraint_checks_disabled():
self.objs_with_deferred_fields = []
for fixture_label in fixture_labels:
self.load_label(fixture_label)
for obj in self.objs_with_deferred_fields:
obj.save_deferred_fields(using=self.using)
# Since we disabled constraint checks, we must manually check for
# any invalid keys that might have been added
table_names = [model._meta.db_table for model in self.models]
try:
connection.check_constraints(table_names=table_names)
except Exception as e:
e.args = ("Problem installing fixtures: %s" % e,)
raise
}}}
I had a closer look at how this works (since I understood that a
transaction already implicitly disables constraint checks) and it turns
out that MySQL/InnoDB is an exception and does *not* defer constraint
checks to the end of the transaction, but instead needs extra handling (so
`constraint_checks_disabled()` is a no-op on most database backends). See
#3615.
--
Ticket URL: <https://code.djangoproject.com/ticket/26552#comment:3>
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