On Thu, Jan 19, 2012 at 1:27 PM, Adrian Holovaty <adr...@holovaty.com>wrote:
> On Thu, Jan 19, 2012 at 12:15 PM, Carl Meyer <c...@oddbird.net> wrote:
> > I don't think Adrian is proposing anything as extensive as #17. What
> > he's proposing (IIUC) wouldn't change the semantics of your sample code
> > at all. All it would do is prepopulate the FK field on the results of a
> > reverse-FK query, so the innermost "book.author" here doesn't need to do
> > a query:
> >
> > for author in Author.objects.all():
> > for book in author.books.all():
> > book.author
> >
> > There wouldn't be any action-at-a-distance with other Book instances.
>
> Right, what Carl said -- no action-at-a-distance, just mere cache
> population on each related object. I don't think there would be a risk
> of backwards-incompatible side effects.
>
>
It would certainly be worth at least a note in the release notes, as it is
a change.
The only situation where I can imagine someone relying on the current
behaviour is in regression tests. I can see code like this being in place
inside a test suite:
def setUp(self):
# We need a foo for every test in this test case
self.foo = Foo.objects.get(id=1)
def test_that_munges_are_really_saved(self):
# Munge the bar. This should also set foo.baz to 12
bar = self.foo.bar
munge_bar(bar)
# check that the Foo really got updated. Before Yestermas, the Foo got
updated
# in memory, but the changes weren't being saved to the db
self.assertEqual(bar.foo.baz, 12)
This code would have been written with the current behaviour in place, and
then completely forgotten about, buried in a suite of tests.
It's easy to argue that the test code is incorrect, and should be using a
different method to check the state of the database, but a test like this
could continue to pass even in the event of an actual regression, and the
developers wouldn't even know that their test was wrong. At least with a
mention in the release notes, [diligent] developers would have been warned,
and could check their code for these sorts of assumptions.
--
Regards,
Ian Clelland
<clell...@gmail.com>
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