#16715: Wrong JOIN with nested null-able foreign keys
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Reporter: sebastian | Owner: nobody
Type: Bug | Status: new
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: 0
Has patch: 1 | UI/UX: 0
Needs tests: 0 |
Easy pickings: 0 |
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Changes (by sebastian):
* needs_better_patch: 1 => 0
Comment:
No problem. I took your patch and adapted it to the current SVN version of
Django ("16715_alternate-redux-r16928.diff"). Some changes were necessary
as there seem to be more instances of `promote_alias[_chain]` in the
current version.
I also added the ability to examine all children of the joins passed to
the new method `promote_joins`. This should make sure that all known
references to a join get updated as well. In fact, this change might
enable us to remove all calls to `promote_alias[_chain]`/`promote_joins`
until just before the final construction of the query. Until now, it seems
that we had to call `promote_alias[_chain]` repeatedly whenever we changed
certain aspects of the query, to ensure the correct join type. However,
this might not be necessary anymore as the new method `promote_joins` does
the promotion recursively (when A->B gets promoted, so do all B->X).
What do you think? Moving the promotion of joins right to the end of the
query construction might simplify the code, since we only had to collect
the requirements of each join (ie. referenced alias, fields, and if the
join itself is nullable) and would add the join type only just before
putting everything together (JOIN_TYPE would remain unset until this very
last step). At least, this seems like the logical thing to do, anyway, but
I don't know if JOIN_TYPE is used for other things during query
construction (I guess it is).
BTW, the new patch too doesn't introduces any new failed tests.
--
Ticket URL: <https://code.djangoproject.com/ticket/16715#comment:15>
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