Re: [Django] #28549: Can't defer() fields from super- and sub-class at the same time

[Django]

#28549: Can't defer() fields from super- and sub-class at the same time
-+-
 Reporter:  Jeremy Kerr  |Owner:  Jeremy
 |  Kerr
 Type:  Bug  |   Status:  closed
Component:  Database layer   |  Version:  master
  (models, ORM)  |
 Severity:  Normal   |   Resolution:  fixed
 Keywords:   | Triage Stage:  Accepted
Has patch:  1|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by Chris Lamb):

 Replying to [comment:9 Simon Charette]:
 > Chris, probably because it was never reported as a regression in the
 first place. Can you confirm this was working in a previous version of
 Django?

 Yep. If I understand your question correctly, from:
 https://bugs.debian.org/876816#5:

 > This bug caused significant performance degradation when we upgraded a
 > Django [1.x] application to a new version that relied on model
 inheritance.

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Re: [Django] #28549: Can't defer() fields from super- and sub-class at the same time

[Django]

#28549: Can't defer() fields from super- and sub-class at the same time
-+-
 Reporter:  Jeremy Kerr  |Owner:  Jeremy
 |  Kerr
 Type:  Bug  |   Status:  closed
Component:  Database layer   |  Version:  master
  (models, ORM)  |
 Severity:  Normal   |   Resolution:  fixed
 Keywords:   | Triage Stage:  Accepted
Has patch:  1|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by Simon Charette):

 Chris, probably because it was never reported as a regression in the first
 place. Can you confirm this was working in a previous version of Django?

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Re: [Django] #28549: Can't defer() fields from super- and sub-class at the same time

[Django]

#28549: Can't defer() fields from super- and sub-class at the same time
-+-
 Reporter:  Jeremy Kerr  |Owner:  Jeremy
 |  Kerr
 Type:  Bug  |   Status:  closed
Component:  Database layer   |  Version:  master
  (models, ORM)  |
 Severity:  Normal   |   Resolution:  fixed
 Keywords:   | Triage Stage:  Accepted
Has patch:  1|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by Chris Lamb):

 Curious why this didn't reach into the 1.11.6 bugfix release.? We are
 carrying this patch in Debian after a user request:

 https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=876816

 (It was the cause of performance regressions in his application so seemed
 sufficiently important to carry)

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Re: [Django] #28549: Can't defer() fields from super- and sub-class at the same time

[Django]

#28549: Can't defer() fields from super- and sub-class at the same time
-+-
 Reporter:  Jeremy Kerr  |Owner:  Jeremy
 |  Kerr
 Type:  Bug  |   Status:  closed
Component:  Database layer   |  Version:  master
  (models, ORM)  |
 Severity:  Normal   |   Resolution:  fixed
 Keywords:   | Triage Stage:  Accepted
Has patch:  1|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Tim Graham ):

 * status:  assigned => closed
 * resolution:   => fixed


Comment:

 In [changeset:"84b7cb7df00192b2f804e2c6fd98b78b5bfd1ffa" 84b7cb7d]:
 {{{
 #!CommitTicketReference repository=""
 revision="84b7cb7df00192b2f804e2c6fd98b78b5bfd1ffa"
 Fixed #28549 -- Fixed QuerySet.defer() with super and subclass fields.

 Previously, deferring fields in different classes didn't omit the
 superclass' deferred field.

 Thanks Simon Charette for the suggested fix.
 }}}

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Re: [Django] #28549: Can't defer() fields from super- and sub-class at the same time

[Django]

#28549: Can't defer() fields from super- and sub-class at the same time
-+-
 Reporter:  Jeremy Kerr  |Owner:  Jeremy
 |  Kerr
 Type:  Bug  |   Status:  assigned
Component:  Database layer   |  Version:  master
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:   | Triage Stage:  Accepted
Has patch:  1|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Simon Charette):

 * cc: Simon Charette (added)


Comment:

 Awesome, thank you for submitting a PR and adding a test!

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Re: [Django] #28549: Can't defer() fields from super- and sub-class at the same time

[Django]

#28549: Can't defer() fields from super- and sub-class at the same time
-+-
 Reporter:  Jeremy Kerr  |Owner:  Jeremy
 |  Kerr
 Type:  Bug  |   Status:  assigned
Component:  Database layer   |  Version:  master
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:   | Triage Stage:  Accepted
Has patch:  1|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Jeremy Kerr):

 * has_patch:  0 => 1


Comment:

 Pull request sent: [https://github.com/django/django/pull/8994 PR]

 Since this is a trivial patch (and my first), I've not added to `AUTHORS`
 or submitted a CLA. Let me know if I need to do either of those.

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Re: [Django] #28549: Can't defer() fields from super- and sub-class at the same time

[Django]

#28549: Can't defer() fields from super- and sub-class at the same time
-+-
 Reporter:  Jeremy Kerr  |Owner:  Jeremy
 |  Kerr
 Type:  Bug  |   Status:  assigned
Component:  Database layer   |  Version:  master
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:   | Triage Stage:  Accepted
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Jeremy Kerr):

 * status:  new => assigned
 * owner:  nobody => Jeremy Kerr


Comment:

 Patch coming.

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Re: [Django] #28549: Can't defer() fields from super- and sub-class at the same time

[Django]

#28549: Can't defer() fields from super- and sub-class at the same time
-+-
 Reporter:  Jeremy Kerr  |Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  master
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:   | Triage Stage:  Accepted
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by Jeremy Kerr):

 Replying to [comment:2 Simon Charette]:
 > I think your intuition is right and that the bug lies in
 `deferred_to_data()`. Could you try replacing `for field in
 model._meta.fields` by `for field in model._meta.local_fields` and see if
 it helps?

 Yep, that seems to fix the issue:

 {{{
 >>> Sub.objects.defer('f1', 'f2').query.sql_with_params()[0]
 u'SELECT "defer_base"."id", "defer_sub"."base_ptr_id" FROM "defer_sub"
 INNER JOIN "defer_base" ON ("defer_sub"."base_ptr_id" =
 "defer_base"."id")'
 }}}

 I was concerned that using `local_fields` would omit inherited fields from
 the query, but looks like that's not the case; inherited (but not
 deferred) fields work fine with that change:

 {{{#!python
 class Base(models.Model):
 f1 = models.CharField(max_length=10)
 f3 = models.CharField(max_length=10)

 class Sub(Base):
 f2 = models.CharField(max_length=10)
 }}}

 {{{
 >>> Sub.objects.defer('f1', 'f2').query.sql_with_params()[0]
 u'SELECT "defer_base"."id", "defer_base"."f3", "defer_sub"."base_ptr_id"
 FROM "defer_sub" INNER JOIN "defer_base" ON ("defer_sub"."base_ptr_id" =
 "defer_base"."id")'
 }}}

 ^^- correctly includes `f3` in the query. Behaviour also look to remain
 correct when only deferring fields from one class too.

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Re: [Django] #28549: Can't defer() fields from super- and sub-class at the same time

[Django]

#28549: Can't defer() fields from super- and sub-class at the same time
-+-
 Reporter:  Jeremy Kerr  |Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  master
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:   | Triage Stage:  Accepted
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Simon Charette):

 * version:  1.11 => master
 * stage:  Unreviewed => Accepted


Comment:

 I think your intuition is right and that the bug lies in
 `deferred_to_data()`. Could you try replacing `for field in
 model._meta.fields` by `for field in model._meta.local_fields` and see if
 it helps?

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Ticket URL: 
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Re: [Django] #28549: Can't defer() fields from super- and sub-class at the same time

[Django]

#28549: Can't defer() fields from super- and sub-class at the same time
-+-
 Reporter:  Jeremy Kerr  |Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  1.11
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:   | Triage Stage:
 |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Jeremy Kerr):

 * cc: Jeremy Kerr (added)
 * component:  Uncategorized => Database layer (models, ORM)
 * type:  Uncategorized => Bug


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[Django] #28549: Can't defer() fields from super- and sub-class at the same time

[Django]

#28549: Can't defer() fields from super- and sub-class at the same time
-+
   Reporter:  Jeremy Kerr|  Owner:  nobody
   Type:  Uncategorized  | Status:  new
  Component:  Uncategorized  |Version:  1.11
   Severity:  Normal |   Keywords:
   Triage Stage:  Unreviewed |  Has patch:  0
Needs documentation:  0  |Needs tests:  0
Patch needs improvement:  0  |  Easy pickings:  0
  UI/UX:  0  |
-+
 Using the models:

 {{{#!python
 from django.db import models

 class Base(models.Model):
 f1 = models.CharField(max_length=10)

 class Sub(Base):
 f2 = models.CharField(max_length=10)
 }}}

 it seems that I can't `defer()` both `f1` and `f2` in a single query:

 {{{
 >>> Sub.objects.defer('f1', 'f2').query.sql_with_params()[0]
 u'SELECT "defer_base"."id", "defer_base"."f1", "defer_sub"."base_ptr_id"
 FROM "defer_sub" INNER JOIN "defer_base" ON ("defer_sub"."base_ptr_id" =
 "defer_base"."id")'
 }}}

 (we're seeing `f1` in the SELECT value list).

 I seem to be able to defer `f1` or `f2` separately though.

 I'm no django hacker, but: it seems as though
 `django.db.models.sql.query.Query.deferred_to_data()` is iterating both
 models in the loop:

 {{{#!python
 #640:
 for model, values in six.iteritems(seen):
 for field in model._meta.fields:
 if field in values:
 continue
 }}}

 ^^- and so is discovering `f1` twice: once as `Base.f1` and again as
 `Sub.f1`. Since the `field in values` test only skips `Base.f1`, we're
 still left with `Sub.f1` in the `workset` dict.

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