#16715: Wrong JOIN with nested null-able foreign keys
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Reporter: sebastian | Owner: nobody
Type: Bug | Status: new
Milestone: | Component: Database layer
Version: SVN | (models, ORM)
Resolution: | Severity: Normal
Triage Stage: Accepted | Keywords: join, values,
Needs documentation: 0 | nested, foreign key, null-able
Patch needs improvement: 1 | Has patch: 1
UI/UX: 0 | Needs tests: 1
| Easy pickings: 0
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Comment (by sebastian):
Thank you both for your feedback. I agree with Alex that the patch is most
probably not in the right place, but again I am still not familiar enough
with the Django internals to have the slightest idea what is happening
here and what would be the appropriate place for fixing this bug.
For the time being, I'll try to come up with some tests similar to the
example in my original report and comment:2.
'''@carljm:''' \\
Regarding a demonstration of where this bug causes a real problem in my
code, see comment:2. That example is a simplified version of what I have
for my current project (including multi-table inheritance
Event→Screening). I wanted to use `select_related` in a schedule of all
upcoming events, so that I don't have to fetch the movie information for
all screenings in the template, but I ended up having all non-screening
events missing in the resulting queryset. This is not the behavior I
expected and this means that I cannot use `select_related`. Without that,
an additional query is issued for each screening where I want to retrieve
the movie information (instead of only a single query for everything). I
tried to work around this with `values` and noticed that this also doesn't
work, as illustrated by my original report (`values` even fails without
using multi-table inheritance, using only simple foreign key relations!).
--
Ticket URL: <https://code.djangoproject.com/ticket/16715#comment:7>
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