Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
-+-
 Reporter:  Kyle Mulka   |Owner:  Akash
 Type:   |  Kumar Sen
  Cleanup/optimization   |   Status:  closed
Component:  Documentation|  Version:  dev
 Severity:  Normal   |   Resolution:  fixed
 Keywords:   | Triage Stage:  Ready for
 |  checkin
Has patch:  1|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by Mariusz Felisiak ):

 In [changeset:"5f2308710b5a3d9f5f135b7ade08214f5c154ec4" 5f230871]:
 {{{
 #!CommitTicketReference repository=""
 revision="5f2308710b5a3d9f5f135b7ade08214f5c154ec4"
 Fixed #30355 -- Doc'd interaction between custom managers and
 prefetch_related().
 }}}

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Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
-+-
 Reporter:  Kyle Mulka   |Owner:  Akash
 Type:   |  Kumar Sen
  Cleanup/optimization   |   Status:  closed
Component:  Documentation|  Version:  dev
 Severity:  Normal   |   Resolution:  fixed
 Keywords:   | Triage Stage:  Ready for
 |  checkin
Has patch:  1|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Mariusz Felisiak ):

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


Comment:

 In [changeset:"eb84c068ed7c2982389b8d331418e99dd9709ff7" eb84c06]:
 {{{
 #!CommitTicketReference repository=""
 revision="eb84c068ed7c2982389b8d331418e99dd9709ff7"
 [4.2.x] Fixed #30355 -- Doc'd interaction between custom managers and
 prefetch_related().

 Backport of 5f2308710b5a3d9f5f135b7ade08214f5c154ec4 from main
 }}}

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Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
-+-
 Reporter:  Kyle Mulka   |Owner:  Akash
 Type:   |  Kumar Sen
  Cleanup/optimization   |   Status:  assigned
Component:  Documentation|  Version:  dev
 Severity:  Normal   |   Resolution:
 Keywords:   | Triage Stage:  Ready for
 |  checkin
Has patch:  1|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Mariusz Felisiak):

 * type:  Bug => Cleanup/optimization
 * stage:  Accepted => Ready for checkin


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Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
---+---
 Reporter:  Kyle Mulka |Owner:  Akash Kumar Sen
 Type:  Bug|   Status:  assigned
Component:  Documentation  |  Version:  dev
 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 Akash Kumar Sen):

 * needs_better_patch:  1 => 0


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Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
---+---
 Reporter:  Kyle Mulka |Owner:  Akash Kumar Sen
 Type:  Bug|   Status:  assigned
Component:  Documentation  |  Version:  dev
 Severity:  Normal |   Resolution:
 Keywords: | Triage Stage:  Accepted
Has patch:  1  |  Needs documentation:  0
  Needs tests:  0  |  Patch needs improvement:  1
Easy pickings:  0  |UI/UX:  0
---+---
Changes (by Mariusz Felisiak):

 * needs_better_patch:  0 => 1


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Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
---+---
 Reporter:  Kyle Mulka |Owner:  Akash Kumar Sen
 Type:  Bug|   Status:  assigned
Component:  Documentation  |  Version:  dev
 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 Akash Kumar Sen):

 * needs_better_patch:  1 => 0


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Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
---+---
 Reporter:  Kyle Mulka |Owner:  Akash Kumar Sen
 Type:  Bug|   Status:  assigned
Component:  Documentation  |  Version:  dev
 Severity:  Normal |   Resolution:
 Keywords: | Triage Stage:  Accepted
Has patch:  1  |  Needs documentation:  0
  Needs tests:  0  |  Patch needs improvement:  1
Easy pickings:  0  |UI/UX:  0
---+---

Comment (by Akash Kumar Sen):

 The possible explanation here is that {{{queryset}}} generated with
 {{{prefetch}}} does not modify the queryset or make a DB query when we are
 fetching the reviews, this is the sole purpose of prefetch, so if we try
 to use a {{{custom manager}}} with {{{prefetch}}} that will violate the
 purpose of using prefetch, hitting 1 extra query every time we try to
 fetch the reviews.
 I will update the docs with this explanation for better understanding
 along with the alternative way using from {{{django.db.models.Prefetch}}}.

 Attaching the testcase for better understanding: https://github.com/Akash-
 Kumar-Sen/django/blob/ticket_30355_3/tests/dummy_tests/tests.py.

 Some feedbacks willbe helpful as I still have a little confusion.

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Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
---+---
 Reporter:  Kyle Mulka |Owner:  Akash Kumar Sen
 Type:  Bug|   Status:  assigned
Component:  Documentation  |  Version:  dev
 Severity:  Normal |   Resolution:
 Keywords: | Triage Stage:  Accepted
Has patch:  1  |  Needs documentation:  0
  Needs tests:  0  |  Patch needs improvement:  1
Easy pickings:  0  |UI/UX:  0
---+---
Changes (by Mariusz Felisiak):

 * needs_better_patch:  0 => 1
 * needs_docs:  1 => 0


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Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
---+---
 Reporter:  Kyle Mulka |Owner:  Akash Kumar Sen
 Type:  Bug|   Status:  assigned
Component:  Documentation  |  Version:  dev
 Severity:  Normal |   Resolution:
 Keywords: | Triage Stage:  Accepted
Has patch:  1  |  Needs documentation:  1
  Needs tests:  0  |  Patch needs improvement:  0
Easy pickings:  0  |UI/UX:  0
---+---
Changes (by Akash Kumar Sen):

 * cc: Akash Kumar Sen (added)
 * owner:  (none) => Akash Kumar Sen
 * has_patch:  0 => 1
 * status:  new => assigned


Comment:

 For me it also seems a documentation issue, as the same results can be
 achieved by obtaining other means. Created a documentation patch
 https://github.com/django/django/pull/16900

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Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
---+
 Reporter:  Kyle Mulka |Owner:  Akshat verma
 Type:  Bug|   Status:  assigned
Component:  Documentation  |  Version:  dev
 Severity:  Normal |   Resolution:
 Keywords: | Triage Stage:  Accepted
Has patch:  0  |  Needs documentation:  1
  Needs tests:  0  |  Patch needs improvement:  0
Easy pickings:  0  |UI/UX:  0
---+
Changes (by Akshat verma):

 * owner:  (none) => Akshat verma
 * status:  new => assigned


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Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
---+
 Reporter:  Kyle Mulka |Owner:  Akshat verma
 Type:  Bug|   Status:  assigned
Component:  Documentation  |  Version:  dev
 Severity:  Normal |   Resolution:
 Keywords: | Triage Stage:  Accepted
Has patch:  1  |  Needs documentation:  1
  Needs tests:  1  |  Patch needs improvement:  1
Easy pickings:  1  |UI/UX:  1
---+
Changes (by Akshat verma):

 * cc: Akshat verma (added)
 * needs_better_patch:  0 => 1
 * needs_tests:  0 => 1
 * easy:  0 => 1
 * has_patch:  0 => 1
 * ui_ux:  0 => 1


Old description:

> When using prefetch and specifying a custom manager to use for a reverse
> relation, Django doesn't filter correctly. Here's an example:
>
> {{{
> class Business(models.Model):
> name = models.CharField(max_length=255)
>
> def approved_reviews(self):
> return self.review_set(manager='approved_reviews').all()
>

> class ApprovedReviewsManager(models.Manager):
> def get_queryset(self):
> return super().get_queryset().filter(status=Review.APPROVED)
>

> class Review(models.Model):
> NEW = 1
> APPROVED = 2
> STATUS_CHOICES = (
> (NEW, 'New'),
> (APPROVED, 'Approved'),
> )
> business = models.ForeignKey(Business)
> text = models.CharField(max_length=255)
> status = models.IntegerField(choices=STATUS_CHOICES, default=NEW)
>
> objects = models.Manager()
> approved_reviews = ApprovedReviewsManager()
>

> class ApprovedReviewsTest(TestCase):
> def test_with_prefetch(self):
> business = Business()
> business.save()
>
> review = Review()
> review.business = business
> review.save()
>
> businesses =
> Business.objects.prefetch_related('review_set').all()
>
> business = businesses[0]
> approved_reviews =
> business.review_set(manager='approved_reviews').all()
>
> self.assertEqual(len(approved_reviews), 0)
> }}}
>
> The full test project is available here:
> https://github.com/mulka/django_prefetch_manager_bug/blob/master/review_site/tests.py

New description:

 When using prefetch and specifying a custom manager to use for a reverse
 relation, Django doesn't filter correctly. Here's an example:

 {{{
 class Business(models.Model):
 name = models.CharField(max_length=255)

 def approved_reviews(self):
 return self.review_set(manager='approved_reviews').all()


 class ApprovedReviewsManager(models.Manager):
 def get_queryset(self):
 return super().get_queryset().filter(status=Review.APPROVED)


 class Review(models.Model):
 NEW = 1
 APPROVED = 2
 STATUS_CHOICES = (
 (NEW, 'New'),
 (APPROVED, 'Approved'),
 )
 business = models.ForeignKey(Business)
 text = models.CharField(max_length=255)
 status = models.IntegerField(choices=STATUS_CHOICES, default=NEW)

 objects = models.Manager()
 approved_reviews = ApprovedReviewsManager()


 class ApprovedReviewsTest(TestCase):
 def test_with_prefetch(self):
 business = Business()
 business.save()

 review = Review()
 review.business = business
 review.save()

 businesses = Business.objects.prefetch_related('review_set').all()

 business = businesses[0]
 approved_reviews =
 business.review_set(manager='approved_reviews').all()

 self.assertEqual(len(approved_reviews), 0)
 }}}

 The full test project is available here:
 
https://github.com/mulka/django_prefetch_manager_bug/blob/master/review_site/tests.py


 #This implementation: by Akshat verma

 class ToppingManager(models.Manager):
 def filter_vegetarian(self):
 return self.filter(is_vegetarian=True)

 #Looks non-standard. docs look like they do a safer method of modifying
 the super-class method for this sort of lazy-eval stuff. #If I rewrite
 your method in that style, it would look like:

 class ToppingManager(models.Manager):
 def filter_vegetarian(self):
 return super(ToppingManager,
 self).get_queryset().filter(is_vegetarian=True)

 #You wouldn't strictly need the super() here, but safer to use it because
 you should know that you want to start with the #models.Manager
 get_queryset method.

--

Comment:

 #This implementation: by Akshat verma

 class ToppingManager(models.Manager):
 def filter_vegetarian(self):
 return self.filter(is_vegetarian=True)

 #Looks non-standard. docs look like they do a safer method of modifying
 the super-class method for this sort of lazy-eval stuff. #If I rewrite
 your method in that style, it would look like:

 class ToppingManager(models.Manager):
 

Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
---+
 Reporter:  Kyle Mulka |Owner:  Akshat verma
 Type:  Bug|   Status:  assigned
Component:  Documentation  |  Version:  dev
 Severity:  Normal |   Resolution:
 Keywords: | Triage Stage:  Accepted
Has patch:  0  |  Needs documentation:  1
  Needs tests:  0  |  Patch needs improvement:  0
Easy pickings:  0  |UI/UX:  0
---+
Changes (by Akshat verma):

 * owner:  (none) => Akshat verma
 * status:  new => assigned


Old description:

> When using prefetch and specifying a custom manager to use for a reverse
> relation, Django doesn't filter correctly. Here's an example:
>
> {{{
> class Business(models.Model):
> name = models.CharField(max_length=255)
>
> def approved_reviews(self):
> return self.review_set(manager='approved_reviews').all()
>

> class ApprovedReviewsManager(models.Manager):
> def get_queryset(self):
> return super().get_queryset().filter(status=Review.APPROVED)
>

> class Review(models.Model):
> NEW = 1
> APPROVED = 2
> STATUS_CHOICES = (
> (NEW, 'New'),
> (APPROVED, 'Approved'),
> )
> business = models.ForeignKey(Business)
> text = models.CharField(max_length=255)
> status = models.IntegerField(choices=STATUS_CHOICES, default=NEW)
>
> objects = models.Manager()
> approved_reviews = ApprovedReviewsManager()
>

> class ApprovedReviewsTest(TestCase):
> def test_with_prefetch(self):
> business = Business()
> business.save()
>
> review = Review()
> review.business = business
> review.save()
>
> businesses =
> Business.objects.prefetch_related('review_set').all()
>
> business = businesses[0]
> approved_reviews =
> business.review_set(manager='approved_reviews').all()
>
> self.assertEqual(len(approved_reviews), 0)
> }}}
>
> The full test project is available here:
> https://github.com/mulka/django_prefetch_manager_bug/blob/master/review_site/tests.py

New description:

 When using prefetch and specifying a custom manager to use for a reverse
 relation, Django doesn't filter correctly. Here's an example:

 {{{
 class Business(models.Model):
 name = models.CharField(max_length=255)

 def approved_reviews(self):
 return self.review_set(manager='approved_reviews').all()


 class ApprovedReviewsManager(models.Manager):
 def get_queryset(self):
 return super().get_queryset().filter(status=Review.APPROVED)


 class Review(models.Model):
 NEW = 1
 APPROVED = 2
 STATUS_CHOICES = (
 (NEW, 'New'),
 (APPROVED, 'Approved'),
 )
 business = models.ForeignKey(Business)
 text = models.CharField(max_length=255)
 status = models.IntegerField(choices=STATUS_CHOICES, default=NEW)

 objects = models.Manager()
 approved_reviews = ApprovedReviewsManager()


 class ApprovedReviewsTest(TestCase):
 def test_with_prefetch(self):
 business = Business()
 business.save()

 review = Review()
 review.business = business
 review.save()

 businesses = Business.objects.prefetch_related('review_set').all()

 business = businesses[0]
 approved_reviews =
 business.review_set(manager='approved_reviews').all()

 self.assertEqual(len(approved_reviews), 0)
 }}}

 The full test project is available here:
 
https://github.com/mulka/django_prefetch_manager_bug/blob/master/review_site/tests.py

--

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Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
---+
 Reporter:  Kyle Mulka |Owner:  (none)
 Type:  Bug|   Status:  new
Component:  Documentation  |  Version:  dev
 Severity:  Normal |   Resolution:
 Keywords: | Triage Stage:  Accepted
Has patch:  0  |  Needs documentation:  1
  Needs tests:  0  |  Patch needs improvement:  0
Easy pickings:  0  |UI/UX:  0
---+
Changes (by Ankur Roy):

 * owner:  Ankur Roy => (none)
 * status:  assigned => new


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Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
---+-
 Reporter:  Kyle Mulka |Owner:  Ankur Roy
 Type:  Bug|   Status:  assigned
Component:  Documentation  |  Version:  dev
 Severity:  Normal |   Resolution:
 Keywords: | Triage Stage:  Accepted
Has patch:  0  |  Needs documentation:  1
  Needs tests:  0  |  Patch needs improvement:  0
Easy pickings:  0  |UI/UX:  0
---+-
Changes (by Ankur Roy):

 * owner:  (none) => Ankur Roy
 * status:  new => assigned


Comment:

 I will review the documentation and add the text as Simon Charette
 described if it hasn't been added already.

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Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
---+
 Reporter:  Kyle Mulka |Owner:  (none)
 Type:  Bug|   Status:  new
Component:  Documentation  |  Version:  dev
 Severity:  Normal |   Resolution:
 Keywords: | Triage Stage:  Accepted
Has patch:  0  |  Needs documentation:  1
  Needs tests:  0  |  Patch needs improvement:  0
Easy pickings:  0  |UI/UX:  0
---+

Comment (by saeldion):

 I'd also weigh in on the bug side. Since the prefetch can happen elsewhere
 its easy to miss. It feels weird that specifying a manager would have no
 effect at all if it's already prefetched. Maybe the prefetch cache could
 be ignored/invalidated if you pass an explicit manager?

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Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
---+
 Reporter:  Kyle Mulka |Owner:  (none)
 Type:  Bug|   Status:  new
Component:  Documentation  |  Version:  master
 Severity:  Normal |   Resolution:
 Keywords: | Triage Stage:  Accepted
Has patch:  0  |  Needs documentation:  1
  Needs tests:  0  |  Patch needs improvement:  0
Easy pickings:  0  |UI/UX:  0
---+
Changes (by Simon Charette):

 * needs_docs:  0 => 1
 * component:  Database layer (models, ORM) => Documentation


Comment:

 I agree that it's more of a documentation issue as `prefetch_related` will
 use the default manager just like accessing a related manager does.

 In other words `Business.objects.prefetch_related('review_set')` will use
 the default manager just like `business.review_set.all()` does.

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Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
-+-
 Reporter:  Kyle Mulka   |Owner:  (none)
 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 robinh00d):

 * owner:  robinh00d => (none)
 * status:  assigned => new


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Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
-+-
 Reporter:  Kyle Mulka   |Owner:  robinh00d
 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 robinh00d):

 * owner:  nobody => robinh00d
 * status:  new => assigned


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Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
-+-
 Reporter:  Kyle Mulka   |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 Kourt Bailey):

 * cc: Kourt Bailey (added)


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Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
-+-
 Reporter:  Kyle Mulka   |Owner:  (none)
 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 robinh00d):

 * status:  assigned => new
 * owner:  robinh00d => (none)


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Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
-+-
 Reporter:  Kyle Mulka   |Owner:  robinh00d
 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 robinh00d):

 * owner:  nobody => robinh00d
 * status:  new => assigned


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Ticket URL: 
Django 
The Web framework for perfectionists with deadlines.

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Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
-+-
 Reporter:  Kyle Mulka   |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 Daniel Hepper):

 * version:  1.11 => master


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Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
-+-
 Reporter:  Kyle Mulka   |Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  1.11
  (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 Daniel Hepper):

 * stage:  Unreviewed => Accepted


Comment:

 I was about to write a patch for the docs on "Using a custom reverse
 manager" to highlight the implication of using prefetch with custom
 managers.

 But thinking about it further made me realize that the prefetch might have
 happened in a completely unrelated part of the code. As a conclusion, I'd
 consider this a bug.

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Ticket URL: 
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Re: [Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
-+-
 Reporter:  Kyle Mulka   |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
-+-

Comment (by Daniel Hepper):

 I've reproduced this behavior with the master branch, but I don't know if
 this is actually a bug or just a case of a somewhat unintuitive API. This
 should at least be documented in the section on using a custom reverse
 manager: https://docs.djangoproject.com/en/2.2/topics/db/queries/#using-a
 -custom-reverse-manager

 A possible workaround would be to use a `django.db.models.Prefetch`
 object:

 {{{
 class ApprovedReviewsTest(TestCase):
 def test_with_prefetch(self):
 business = Business()
 business.save()

 review = Review()
 review.business = business
 review.save()

 prefetch_approved_reviews = Prefetch('review_set',
 queryset=Review.approved_reviews.all())
 businesses =
 Business.objects.prefetch_related(prefetch_approved_reviews).all()

 business = businesses[0]
 approved_reviews =
 business.review_set(manager='approved_reviews').all()

 self.assertEqual(len(approved_reviews), 0)
 }}}


 In this example, you don't even have to specify the custom manager,
 `business.review_set.all()` would give you the same result.

 The underlying issue is that there is only a single prefetched object
 cache per field, see
 
https://github.com/django/django/blob/de7f6b51b21747e19e90d9e3e04e0cdbf84e8a75/django/db/models/fields/related_descriptors.py#L607

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[Django] #30355: Specifying custom manager doesn't work with prefetch

[Django]

#30355: Specifying custom manager doesn't work with prefetch
-+-
   Reporter:  Kyle   |  Owner:  nobody
  Mulka  |
   Type:  Bug| Status:  new
  Component:  Database   |Version:  1.11
  layer (models, ORM)|
   Severity:  Normal |   Keywords:
   Triage Stage: |  Has patch:  0
  Unreviewed |
Needs documentation:  0  |Needs tests:  0
Patch needs improvement:  0  |  Easy pickings:  0
  UI/UX:  0  |
-+-
 When using prefetch and specifying a custom manager to use for a reverse
 relation, Django doesn't filter correctly. Here's an example:

 {{{
 class Business(models.Model):
 name = models.CharField(max_length=255)

 def approved_reviews(self):
 return self.review_set(manager='approved_reviews').all()


 class ApprovedReviewsManager(models.Manager):
 def get_queryset(self):
 return super().get_queryset().filter(status=Review.APPROVED)


 class Review(models.Model):
 NEW = 1
 APPROVED = 2
 STATUS_CHOICES = (
 (NEW, 'New'),
 (APPROVED, 'Approved'),
 )
 business = models.ForeignKey(Business)
 text = models.CharField(max_length=255)
 status = models.IntegerField(choices=STATUS_CHOICES, default=NEW)

 objects = models.Manager()
 approved_reviews = ApprovedReviewsManager()


 class ApprovedReviewsTest(TestCase):
 def test_with_prefetch(self):
 business = Business()
 business.save()

 review = Review()
 review.business = business
 review.save()

 businesses = Business.objects.prefetch_related('review_set').all()

 business = businesses[0]
 approved_reviews =
 business.review_set(manager='approved_reviews').all()

 self.assertEqual(len(approved_reviews), 0)
 }}}

 The full test project is available here:
 
https://github.com/mulka/django_prefetch_manager_bug/blob/master/review_site/tests.py

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