Re: [Django] #20241: QuerySets with callable filter args have said args evaluated only once

[Django]

#20241: QuerySets with callable filter args have said args evaluated only once
-+-
 Reporter:   |Owner:  nobody
  christopher.m.pike@…   |   Status:  closed
 Type:  Bug  |  Version:  1.5
Component:  Database layer   |   Resolution:  duplicate
  (models, ORM)  | Triage Stage:  Accepted
 Severity:  Normal   |  Needs documentation:  0
 Keywords:   |  Patch needs improvement:  0
Has patch:  0|UI/UX:  0
  Needs tests:  0|
Easy pickings:  0|
-+-
Changes (by timo):

 * status:  new => closed
 * resolution:   => duplicate


Comment:

 We're going to deprecate callable queryset filter arguments -- see #11629.

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Re: [Django] #20241: QuerySets with callable filter args have said args evaluated only once

[Django]

#20241: QuerySets with callable filter args have said args evaluated only once
-+-
 Reporter:   |Owner:  nobody
  christopher.m.pike@…   |   Status:  new
 Type:  Bug  |  Version:  1.5
Component:  Database layer   |   Resolution:
  (models, ORM)  | Triage Stage:  Accepted
 Severity:  Normal   |  Needs documentation:  0
 Keywords:   |  Patch needs improvement:  0
Has patch:  0|UI/UX:  0
  Needs tests:  0|
Easy pickings:  0|
-+-

Comment (by bmispelon):

 Turns out this issue was reported a while ago: #10466

 I closed the other one since I think there's more information in the
 discussion of this ticket.

 I don't know anything about the internals of querysets but if this issue
 is that tricky to fix, I'd be in favor of dropping it entirely.

 For one, it's never been documented and secondly, it's not very useful
 since the callable is evaluated immediately (all it does is save the user
 from typing a pair of parentheses).

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Re: [Django] #20241: QuerySets with callable filter args have said args evaluated only once

[Django]

#20241: QuerySets with callable filter args have said args evaluated only once
-+-
 Reporter:   |Owner:  nobody
  christopher.m.pike@…   |   Status:  new
 Type:  Bug  |  Version:  1.5
Component:  Database layer   |   Resolution:
  (models, ORM)  | Triage Stage:  Accepted
 Severity:  Normal   |  Needs documentation:  0
 Keywords:   |  Patch needs improvement:  0
Has patch:  0|UI/UX:  0
  Needs tests:  0|
Easy pickings:  0|
-+-

Comment (by akaariai):

 The reasons why fixing this isn't easy:
   1. The WhereNode._prepare_data() call is done at .filter() call time.
 The _prepare_data() method does some transformations based on the type of
 the value, specifically datetime.datetime values will cause some
 transformations. If the callable is timezone.now, then the lookup will not
 work correctly.
   2. The value will need to be resolved for isnull lookups (isnull=True
 lookups will need to produce LEFT OUTER JOINs and join promotion is done
 at .filter() call time).
   3. Some advanced constructs do not work correctly - returning F()
 objects for example (they don't work correctly even now).

 At least no.1 will need to be fixed if the value resolving is deferred to
 query execution time. So, _prepare_data will need to be moved to query
 execution time. The only problematic case seems to be iterators - they
 must not be consumed multiple times, and this would happen if all of
 _prepare_data is moved to query execution time.

 Fixing number 2 and 3 properly will be really hard (need to alter the join
 types at execution time, and that is problematic for multiple reasons, not
 least because the query should not be altered at execution time...). But,
 I am not sure if those need to be fixed at all, they could be documented
 as known limitations when using callable arguments. In practice the
 limitations wouldn't cause much trouble to users, and it is easy enough to
 raise errors in problematic cases.

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Re: [Django] #20241: QuerySets with callable filter args have said args evaluated only once

[Django]

#20241: QuerySets with callable filter args have said args evaluated only once
-+-
 Reporter:   |Owner:  nobody
  christopher.m.pike@…   |   Status:  new
 Type:  Bug  |  Version:  1.5
Component:  Database layer   |   Resolution:
  (models, ORM)  | Triage Stage:  Accepted
 Severity:  Normal   |  Needs documentation:  0
 Keywords:   |  Patch needs improvement:  0
Has patch:  0|UI/UX:  0
  Needs tests:  0|
Easy pickings:  0|
-+-

Comment (by bmispelon):

 Replying to [comment:2 michael.c.urbanski@…]:
 > I was under the impression that callables in QuerySets, like callables
 in fields, were called as they were used.

 I would have thought so too, but it appears it's not the case.

 I've opened #20249 to fix the tutorial while this ticket remains open
 (fixing this ticket is likely more complicated than amending the
 documentation).

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Re: [Django] #20241: QuerySets with callable filter args have said args evaluated only once

[Django]

#20241: QuerySets with callable filter args have said args evaluated only once
-+-
 Reporter:   |Owner:  nobody
  christopher.m.pike@…   |   Status:  new
 Type:  Bug  |  Version:  1.5
Component:  Database layer   |   Resolution:
  (models, ORM)  | Triage Stage:  Accepted
 Severity:  Normal   |  Needs documentation:  0
 Keywords:   |  Patch needs improvement:  0
Has patch:  0|UI/UX:  0
  Needs tests:  0|
Easy pickings:  0|
-+-

Comment (by michael.c.urbanski@…):

 I was under the impression that callables in QuerySets, like callables in
 fields, were called as they were used.  Why pass in a callable if it's
 only evaluated once?

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Re: [Django] #20241: QuerySets with callable filter args have said args evaluated only once

[Django]

#20241: QuerySets with callable filter args have said args evaluated only once
-+-
 Reporter:   |Owner:  nobody
  christopher.m.pike@…   |   Status:  new
 Type:  Bug  |  Version:  1.5
Component:  Database layer   |   Resolution:
  (models, ORM)  | Triage Stage:  Accepted
 Severity:  Normal   |  Needs documentation:  0
 Keywords:   |  Patch needs improvement:  0
Has patch:  0|UI/UX:  0
  Needs tests:  0|
Easy pickings:  0|
-+-
Changes (by bmispelon):

 * severity:  Release blocker => Normal
 * cc: bmispelon@… (added)
 * needs_better_patch:   => 0
 * needs_tests:   => 0
 * needs_docs:   => 0
 * stage:  Unreviewed => Accepted


Comment:

 I can reproduce this issue.

 Using the following code, you can see that the callable arguments are
 indeed only evaluated once (when the urls.py file is read for the first
 time):

 {{{
 #!python
 from django.conf.urls import patterns, include, url
 from django.views.generic import ListView
 from django.utils import timezone

 from .models import Poll


 def foo():
 print('called')
 return timezone.now()


 urlpatterns = patterns('',
 url('^$', ListView.as_view(
 queryset=Poll.objects.filter(pub_date__lte=foo),
 )),
 )
 }}}

 However, unlike what it described on the linked SO post, I find that the
 issue is present on master, 1.5, and 1.4 so I don't think it's a
 regression.

 This feature (passing callable arguments to `filter`) is only mentionned
 in the 5th part of the tutorial and it's not documented anywhere else (see
 #11629).

 I'm not sure if this is a bug or intended behavior.

 I the issue here lies with the documentation and I would suggest re-
 writing that part of the tutorial.

 With normal pyhton code, anything sitting at the top-level of a module is
 evaluated when the file is read.
 In the case of querysets, they do magic things to delay their evaluation
 which makes the code kind-of work but I don't think it's a good habit to
 teach.

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[Django] #20241: QuerySets with callable filter args have said args evaluated only once

[Django]

#20241: QuerySets with callable filter args have said args evaluated only once
--+
 Reporter:  christopher.m.pike@…  |  Owner:  nobody
 Type:  Bug   | Status:  new
Component:  Database layer (models, ORM)  |Version:  1.5
 Severity:  Release blocker   |   Keywords:
 Triage Stage:  Unreviewed|  Has patch:  0
Easy pickings:  0 |  UI/UX:  0
--+
 I was going to write out a longer ticket, but this SO post does a good job
 of describing my situation.

 http://stackoverflow.com/questions/15666199/new-rows-created-in-django-
 admin-arent-displayed-on-site

 I'm having the same issue, but I'm using Python 2.7.3 with PostgreSQL with
 Django 1.5.1.

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