#17014: prefetch_related tests needed: recursive default prefetch_related
structures, diamond structures
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Reporter: akaariai | Owner: nobody
Type: Bug | Status: new
Component: Database layer (models, ORM) | Version: 1.3
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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I haven't tested these two cases with the trunk version, so I don't know
if these mentioned problems work with prefetch_related or not. At least
both of these need tests, though.
Recursive default queryset prefetch_related calls need test. The simplest
case is:
{{{
class PeopleDefManager(models.Manager):
def get_query_set(self):
return super(PeopleDefmanager,
self).get_query_set().prefetch_related('reverse_best_friend')
class People(models.Model):
name = models.TextField()
best_friend = models.ForeignKey('self',
related_name='reverse_best_friend')
objects = PeopleDefManager()
}}}
I did some work for #17000, and my version for that ticket had a very
serious problem. The problem was indefinite recursion which ended up
eating all the memory and going to OOM killer. That is a pretty bad
failure condition... I ended up tracking which prefetches had been done
and bailing out if recursion was detected. And having a hard limit of
doing at most 200 prefetch_one_level calls in one queryset. The limit
could be much lower while still allowing for infinite recursion. I haven't
tested if the trunk version suffers from this. At least tests needed in
any case.
Another condition that needs testing is:
{{{
A
/ \
through / \ through
b_set / \ c_set
B C
\ /
through d_set \ / through d_set
\ /
D
}}}
It is important that both B and C have a field with same name to D. I
don't know if this works or not, but this also needs tests at least.
--
Ticket URL: <https://code.djangoproject.com/ticket/17014>
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