I believe that's as designed. There's this part in the documentation of
"Database transactions":
Callbacks are not run until autocommit is restored on the connection
following the commit (because otherwise any queries done in a callback
would open an implicit transaction, preventing the connection from going
back into autocommit mode).
So on_commit is meant as a connection level hook, not a transaction level
one.
On Mon, May 16, 2016 at 3:10 PM, <barthel...@infobart.com> wrote:
> Hi,
>
> I believe that I encountered a bug or at least a serious limitation with
> transaction.on_commit in Django 1.9.x. Essentially, the on_commit hooks
> seem to be tied to the database connection instead of the transaction. This
> means that unrelated transactions may trigger on_commit hooks, which
> results in undesired execution order. Here is an example:
>
> from django.db import transaction
> from foobar.models import Model1, Model2
>
>
> @transaction.atomic
> def outer():
> print("START - OUTER")
> for i in range(4):
> f1(i)
> print("END - OUTER")
>
>
> @transaction.atomic
> def f1(i):
> model = Model1(description="test {0}".format(i))
> model.save()
> transaction.on_commit(lambda: commit_hook(model, i))
>
>
> def commit_hook(model, i):
> print("START - on_commit hook")
> f2(i)
> print("STOP - on_commit hook")
>
>
> @transaction.atomic
> def f2(i):
> print("CALLING F2")
> model = Model2(description="test {0}".format(i))
> model.save()
>
>
> Some quick explanations:
>
> - outer is the outermost atomic block. f1 will only create a savepoint().
> This works as expected, there is only one commit (trace erased for
> simplicity).
> - f2 is wrapped in an "outermost" atomic block and indeed, f2 will be
> called four times and there will be four commits (trace erased for
> simplicity).
> - f1 register a commit_hook. I expect that at the end of outer(), all
> commit hooks will be called.
>
>
> The expected trace is:
> START - OUTER
> END - OUTER
> START - on_commit hook
> CALLING F2
> STOP - on_commit hook
> START - on_commit hook
> CALLING F2
> STOP - on_commit hook
> START - on_commit hook
> CALLING F2
> STOP - on_commit hook
> START - on_commit hook
> CALLING F2
> STOP - on_commit hook
>
> The actual trace (f2 is triggering the on_commit hooks registered in
> f1/outer):
> START - OUTER
> END - OUTER
> START - on_commit hook
> CALLING F2
> START - on_commit hook
> CALLING F2
> START - on_commit hook
> CALLING F2
> START - on_commit hook
> CALLING F2
> STOP - on_commit hook
> STOP - on_commit hook
> STOP - on_commit hook
> STOP - on_commit hook
>
> I wanted to know if someone encountered this issue or if I am
> misunderstanding on_commit before opening a ticket.
>
> Regards,
> Bart
>
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