[Django] #18743: select_for_update() silently ignored on aggregate queries
Django
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Reporter: anonymous | Owner: nobody
Type: Bug | Status: new
Component: Database layer (models, ORM) | Version: 1.4
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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When used on aggregate queries, the new 1.4 select_for_update() silently
omits "FOR UPDATE" from the generated SQL. Instead, I would expect Django
to raise a database exception, as "SELECT FOR UPDATE" on an aggregate
query does not make sense. For instance, raw PostgreSQL yields an error
message:
# select max(id) from mytable for update;
ERROR: SELECT FOR UPDATE/SHARE is not allowed with aggregate functions
In constrast, a Django query containing an aggregate like Max() and also
using select_for_update() does not raise an exception.
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Ticket URL: <https://code.djangoproject.com/ticket/18743>
Django <https://code.djangoproject.com/>
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Django
Reporter: anonymous | Owner: nobody
Type: Bug | Status: closed
Component: Database layer | Version: 1.4
(models, ORM) | Resolution: wontfix
Severity: Normal | Triage Stage:
Keywords: | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
Changes (by nicolas):
* status: new => closed
* needs_better_patch: => 0
* resolution: => wontfix
* needs_tests: => 0
* needs_docs: => 0
Comment:
As you said, select_for_update on an aggregate wouldn't make any sense.
The correct behaviour here is to silently ignore it and execute the
aggregate. This is similar to what happens in databases that don't support
select_for_update like SQLite
(https://docs.djangoproject.com/en/dev/ref/models/querysets/#select-for-
update).
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Ticket URL: <https://code.djangoproject.com/ticket/18743#comment:1>
Django
Reporter: anonymous | Owner: nobody
Type: Bug | Status: closed
Component: Database layer | Version: 1.4
(models, ORM) | Resolution: wontfix
Severity: Normal | Triage Stage:
Keywords: | Unreviewed
Has patch: 0 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
Comment (by Josh Kupershmidt <schmiddy@…>):
I agree with the OP, as I was pretty surprised by Django's behavior here
myself recently when attempting to use select_for_update() in combination
with a Sum() aggregate. I would have liked to see an explicit error in
this case. And I think this kind of confusion may be common, see e.g.
http://stackoverflow.com/questions/18455473/why-cant-i-use-select-for-
update-with-aggregate-functions
I think if we can raise an Exception for unsupported operations such as
in, say:
Passing nowait=True to select_for_update() using database backends that
do not support nowait, such as MySQL, will cause a DatabaseError to be
raised.
Then there is a good case to be made for raising an Exception here.
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Ticket URL: <https://code.djangoproject.com/ticket/18743#comment:2>