Re: [Django] #34067: django.core.Paginator wrong query slicing

[Django]

#34067: django.core.Paginator wrong query slicing
-+-
 Reporter:  Hristo Trendafilov   |Owner:  nobody
 Type:  Bug  |   Status:  closed
Component:  Core (Other) |  Version:  3.2
 Severity:  Normal   |   Resolution:  needsinfo
 Keywords:   | Triage Stage:
  Paginator,slice,queryset   |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Mariusz Felisiak):

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


Comment:

 > It is Django fault for those reasons:
 >
 > * `order_by` might be complicated but is supported by the framework
 > * Chained `order_by` is also supported

 Yes, but you should be aware what you are using in the `ORDER BY` clause
 and that some fields may cause issues, e.g. multi-valued fields (see
 [https://docs.djangoproject.com/en/stable/ref/models/querysets/#order-by
 notes in docs]). Django cannot decide for you.

 > * queryset slicing is a feature of Django queryset API.
 > * queryset slicing should act like list and string slicing and namely to
 provide you with results `[ from : to ]` indexes provided and not to
 change or lose data in between. Or in other words - what is passed in the
 `Paginator.object_list` should be just sliced `[ from : to ]`. `Paginator`
 should never care for the queryset, what is the ordering of the queryset,
 what is excluded and so on - it should just work with it.

 This would require fetching all results and slicing on the Python side not
 in the database which is very ineffective and would cause many performance
 issues.

 > * changing `paginate_by` to `10` or greater fixes the problem.
 `paginate_by` is a standard and documented Django ListView setting.
 > * changing `order_by` to some other `order_by` also fixes the problem.
 `order_by` should work the same or if any limitations those should be well
 documented

 Limitations are mostly documented, but we cannot document all caveats.

 > P.S. That is also happening in Django 2.2

 Django 2.2 is not supported anymore, and Django 3.2 is in extended support
 so it receives only security patches.


 I understand that you spend a lot of time trying to debug your issue, but
 we don't have your app, your data, and your database, so we're unable to
 help. Also, Trac is not a support channel.

 I'd like to highly recommend using one of
 [https://code.djangoproject.com/wiki/TicketClosingReasons/UseSupportChannels
 support channel] where folks will help you. If you'll still be convinced
 that Django is at fault, then please attach a sample minimal project that
 reproduces the issue.

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Re: [Django] #34067: django.core.Paginator wrong query slicing

[Django]

#34067: django.core.Paginator wrong query slicing
-+-
 Reporter:  Hristo Trendafilov   |Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Core (Other) |  Version:  3.2
 Severity:  Normal   |   Resolution:
 Keywords:   | Triage Stage:
  Paginator,slice,queryset   |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Hristo Trendafilov):

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


-- 
Ticket URL: 
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Re: [Django] #34067: django.core.Paginator wrong query slicing

[Django]

#34067: django.core.Paginator wrong query slicing
-+-
 Reporter:  Hristo Trendafilov   |Owner:  nobody
 Type:  Bug  |   Status:  closed
Component:  Core (Other) |  Version:  3.2
 Severity:  Normal   |   Resolution:  needsinfo
 Keywords:   | Triage Stage:
  Paginator,slice,queryset   |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by Hristo Trendafilov):

 Replying to [comment:6 Hristo Trendafilov]:

 Just added that in the description. At the end of the day, it is expected
 Paginator just slice whatever is provided, not to change or lose data in
 between. Changing `paginate_by` leads to fix and that is a feature of
 Django.

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Ticket URL: 
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Re: [Django] #34067: django.core.Paginator wrong query slicing

[Django]

#34067: django.core.Paginator wrong query slicing
-+-
 Reporter:  Hristo Trendafilov   |Owner:  nobody
 Type:  Bug  |   Status:  closed
Component:  Core (Other) |  Version:  3.2
 Severity:  Normal   |   Resolution:  needsinfo
 Keywords:   | Triage Stage:
  Paginator,slice,queryset   |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Description changed by Hristo Trendafilov:

Old description:

> A have a ListView defined like so:
>
> {{{
> class AllPracticesListView(LoginRequiredMixin, PermissionRequiredMixin,
> ListView, ToolBoxFunctions):
> template_name = 'practice_list.html'
> model = Practice
> paginate_by = 6
> permission_required = 'customauth.access_practices'
>
> def get_queryset(self):
> qs = self.get_all_practices_by_user().order_by(
> 'company_branch__pk',
> 'practice_profile__personal_profile__last_name').prefetch_related('practice_profile')
>
> # method < get_all_practices_by_user > is a toolbox method that
> returns:
> #
> Practice.objects.filter(company_branch__owner=self.request.user).order_by('pk')
>
> return qs
>
> }}}
>
> Models are defined like so:
> {{{
>
>  class Practice(models.Model):
> company_branch = models.ForeignKey(
>  CompanyBranch,
>  on_delete=models.PROTECT,
>  related_name='practices',
> )
> # CompanyBranch model has an owner field which ForeignKey
> to the user model
>
> practice_profile = models.ForeignKey(
> PracticeProfile,
> on_delete=models.PROTECT,
> related_name='practices',
> )
>
> class PracticeProfile(models.Model):
> personal_profile = models.ForeignKey(
> PersonalProfile,
> on_delete=models.PROTECT,
> blank=True,
> null=True,
> )
> # PersonalProfile model has a field called <
> last_name >
> }}}
> Or schematically:
> {{{
> Practice object relations:
>   -> CompanyBranch
>   -> PracticeProfile
>   -> PersonalProfile /*NULLABLE RELATION/
>
> }}}
>
> When the code is run, the view does not display results correctly.
>
> I did like so to get the WRONG result:
> Added a breakpoint on  {{{Paginator._get_page}}} return statement
>
> Queryset is passed okay and is available in
> {{{Paginator.object_list}}}
>
> But in the args of {{{Paginator._get_page}}} the queryset is totally
> different than expected / should be a slice from the first six elements
> of {{{Paginator.object_list}}} /
>
> I have tried to add a breakpoint like so
> [[Image(https://imgur.com/SdaQUt6)]]
> Then I get this result [[Image(https://imgur.com/5zzLNV0)]].
>
> As you can see, PKs 1632, 1624, etc. are missing, objects are
> different/marked red and purple/, and are actually removed and never
> shown in the view.
>
> If you run slice manually at this point - everything is again fine
> [[Image(https://imgur.com/yvn8KMO)]]
> This happens only on NULL PersonalProfile objects.
>

> I did like so to get OKAY results:
>
> 1. Added a simple breakpoint is added on {{{Paginator.page}}} like so
> [[Image(https://imgur.com/d7J5BMZ)]] and that breakpoint is just run then
> the result is okay [[Image(https://imgur.com/ILDHAMN)]]
>
> 2. changed paginate_by to 10
>
> 3. changed {{{order_by}}} in {{{get_queryset}}} to {{{-pk}}}
>
> 4. call again the {{{page = paginator.page(page_number)}}}
>
> P.S. That is also happening in django 2.2

New description:

 A have a ListView defined like so:

 {{{
 class AllPracticesListView(LoginRequiredMixin, PermissionRequiredMixin,
 ListView, ToolBoxFunctions):
 template_name = 'practice_list.html'
 model = Practice
 paginate_by = 6
 permission_required = 'customauth.access_practices'

 def get_queryset(self):
 qs = self.get_all_practices_by_user().order_by(
 'company_branch__pk',
 
'practice_profile__personal_profile__last_name').prefetch_related('practice_profile')

 # method < get_all_practices_by_user > is a toolbox method that
 returns:
 #
 Practice.objects.filter(company_branch__owner=self.request.user).order_by('pk')

 return qs

 }}}

 Models are defined like so:
 {{{

  class Practice(models.Model):
 company_branch = models.ForeignKey(
  CompanyBranch,

Re: [Django] #34067: django.core.Paginator wrong query slicing

[Django]

#34067: django.core.Paginator wrong query slicing
-+-
 Reporter:  Hristo Trendafilov   |Owner:  nobody
 Type:  Bug  |   Status:  closed
Component:  Core (Other) |  Version:  3.2
 Severity:  Normal   |   Resolution:  needsinfo
 Keywords:   | Triage Stage:
  Paginator,slice,queryset   |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by Tim Graham):

 You should explain why Django is at fault. I'm guessing that your
 complicated query might not be returning results in a consistent order.
 There's nothing Django can do about that.

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

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Re: [Django] #34067: django.core.Paginator wrong query slicing

[Django]

#34067: django.core.Paginator wrong query slicing
-+-
 Reporter:  Hristo Trendafilov   |Owner:  nobody
 Type:  Bug  |   Status:  closed
Component:  Core (Other) |  Version:  3.2
 Severity:  Normal   |   Resolution:  needsinfo
 Keywords:   | Triage Stage:
  Paginator,slice,queryset   |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Old description:

> A have a ListView defined like so:
>
> {{{
> class AllPracticesListView(LoginRequiredMixin, PermissionRequiredMixin,
> ListView, ToolBoxFunctions):
> template_name = 'practice_list.html'
> model = Practice
> paginate_by = 6
> permission_required = 'customauth.access_practices'
>
> def get_queryset(self):
> qs = self.get_all_practices_by_user().order_by(
> 'company_branch__pk',
> 'practice_profile__personal_profile__last_name').prefetch_related('practice_profile')
>
> # method < get_all_practices_by_user > is a toolbox method that
> returns:
> #
> Practice.objects.filter(company_branch__owner=self.request.user).order_by('pk')
>
> return qs
>
> }}}
>
> Models are defined like so:
> {{{
>
>  class Practice(models.Model):
> company_branch = models.ForeignKey(
>  CompanyBranch,
>  on_delete=models.PROTECT,
>  related_name='practices',
> )
> # CompanyBranch model has an owner field which ForeignKey
> to the user model
>
> practice_profile = models.ForeignKey(
> PracticeProfile,
> on_delete=models.PROTECT,
> related_name='practices',
> )
>
> class PracticeProfile(models.Model):
> personal_profile = models.ForeignKey(
> PersonalProfile,
> on_delete=models.PROTECT,
> blank=True,
> null=True,
> )
> # PersonalProfile model has a field called <
> last_name >
> }}}
> Or schematically:
> {{{
> Practice object relations:
>   -> CompanyBranch
>   -> PracticeProfile
>   -> PersonalProfile /*NULLABLE RELATION/
>
> }}}
>
> When the code is run, the view does not display results correctly.
>
> I did like so to get the WRONG result:
> Added a breakpoint on  {{{Paginator._get_page}}} return statement
>
> Queryset is passed okay and is available in
> {{{Paginator.object_list}}}
>
> But in the args of {{{Paginator._get_page}}} the queryset is totally
> different than expected / should be a slice from the first six elements
> of {{{Paginator.object_list}}} /
>
> I have added a breakpoint like so [[Image(https://imgur.com/SdaQUt6)]]. I
> do not use the method itself, just stopped the execution to check what
> data the `Page` class itself is called with.
>
> Then I get this result [[Image(https://imgur.com/5zzLNV0)]].
>
> As you can see, PKs 1632, 1624, etc. are missing, objects are
> different/marked red and purple/, and are actually removed and never
> shown in the view.
>
> If you run slice manually at this point - everything is again fine
> [[Image(https://imgur.com/yvn8KMO)]]
> This happens only on NULL PersonalProfile objects.
>

> I did like so to get OKAY results:
>
> 1. Added a simple breakpoint is added on {{{Paginator.page}}} like so
> [[Image(https://imgur.com/d7J5BMZ)]] and that breakpoint is just run then
> the result is okay [[Image(https://imgur.com/ILDHAMN)]]
>
> 2. changed paginate_by to 10
>
> 3. changed {{{order_by}}} in {{{get_queryset}}} to {{{-pk}}}
>
> 4. call again the {{{page = paginator.page(page_number)}}}
>
> P.S. That is also happening in django 2.2

New description:

 A have a ListView defined like so:

 {{{
 class AllPracticesListView(LoginRequiredMixin, PermissionRequiredMixin,
 ListView, ToolBoxFunctions):
 template_name = 'practice_list.html'
 model = Practice
 paginate_by = 6
 permission_required = 'customauth.access_practices'

 def get_queryset(self):
 qs = self.get_all_practices_by_user().order_by(
 'company_branch__pk',
 
'practice_profile__personal_profile__last_name').prefetch_related('practice_profile')

 # method < get_all_practices_by_user > is a toolbox method that
 returns:
 #
 Practice.objects.filter(company_branch__owner=self.request.user).order_by('pk')

 return qs

 }}}

 Models are defined like so:
 {{{

  class Practice(models.Model):
 comp

Re: [Django] #34067: django.core.Paginator wrong query slicing

[Django]

#34067: django.core.Paginator wrong query slicing
-+-
 Reporter:  Hristo Trendafilov   |Owner:  nobody
 Type:  Bug  |   Status:  closed
Component:  Core (Other) |  Version:  3.2
 Severity:  Normal   |   Resolution:  needsinfo
 Keywords:   | Triage Stage:
  Paginator,slice,queryset   |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Old description:

> A have a ListView defined like so:
>
> {{{
> class AllPracticesListView(LoginRequiredMixin, PermissionRequiredMixin,
> ListView, ToolBoxFunctions):
> template_name = 'practice_list.html'
> model = Practice
> paginate_by = 6
> permission_required = 'customauth.access_practices'
>
> def get_queryset(self):
> qs = self.get_all_practices_by_user().order_by(
> 'company_branch__pk',
> 'practice_profile__personal_profile__last_name').prefetch_related('practice_profile')
>
> # method < get_all_practices_by_user > is a toolbox method that
> returns:
> #
> Practice.objects.filter(company_branch__owner=self.request.user).order_by('pk')
>
> return qs
>
> }}}
>
> Models are defined like so:
> {{{
>
>  class Practice(models.Model):
> company_branch = models.ForeignKey(
>  CompanyBranch,
>  on_delete=models.PROTECT,
>  related_name='practices',
> )
> # CompanyBranch model has an owner field which ForeignKey
> to the user model
>
> practice_profile = models.ForeignKey(
> PracticeProfile,
> on_delete=models.PROTECT,
> related_name='practices',
> )
>
> class PracticeProfile(models.Model):
> personal_profile = models.ForeignKey(
> PersonalProfile,
> on_delete=models.PROTECT,
> blank=True,
> null=True,
> )
> # PersonalProfile model has a field called <
> last_name >
> }}}
> Or schematically:
> {{{
> Practice object relations:
>   -> CompanyBranch
>   -> PracticeProfile
>   -> PersonalProfile /*NULLABLE RELATION/
>
> }}}
>
> When the code is run, the view does not display results correctly.
>
> I did like so to get the WRONG result:
> Added a breakpoint on  {{{Paginator._get_page}}} return statement
>
> Queryset is passed okay and is available in
> {{{Paginator.object_list}}}
>
> But in the args of {{{Paginator._get_page}}} the queryset is totally
> different than expected / should be a slice from the first six elements
> of {{{Paginator.object_list}}} /
>
> I have tried to add a breakpoint like so
> [[Image(https://imgur.com/SdaQUt6)]]
> Then I get this result [[Image(https://imgur.com/5zzLNV0)]].
>
> As you can see, PKs 1632, 1624, etc. are missing, objects are
> different/marked red and purple/, and are actually removed and never
> shown in the view.
>
> If you run slice manually at this point - everything is again fine
> [[Image(https://imgur.com/yvn8KMO)]]
> This happens only on NULL PersonalProfile objects.
>

> I did like so to get OKAY results:
>
> 1. Added a simple breakpoint is added on {{{Paginator.page}}} like so
> [[Image(https://imgur.com/d7J5BMZ)]] and that breakpoint is just run then
> the result is okay [[Image(https://imgur.com/ILDHAMN)]]
>
> 2. changed paginate_by to 10
>
> 3. changed {{{order_by}}} in {{{get_queryset}}} to {{{-pk}}}
>
> 4. call again the {{{page = paginator.page(page_number)}}}
>
> P.S. That is also happening in django 2.2

New description:

 A have a ListView defined like so:

 {{{
 class AllPracticesListView(LoginRequiredMixin, PermissionRequiredMixin,
 ListView, ToolBoxFunctions):
 template_name = 'practice_list.html'
 model = Practice
 paginate_by = 6
 permission_required = 'customauth.access_practices'

 def get_queryset(self):
 qs = self.get_all_practices_by_user().order_by(
 'company_branch__pk',
 
'practice_profile__personal_profile__last_name').prefetch_related('practice_profile')

 # method < get_all_practices_by_user > is a toolbox method that
 returns:
 #
 Practice.objects.filter(company_branch__owner=self.request.user).order_by('pk')

 return qs

 }}}

 Models are defined like so:
 {{{

  class Practice(models.Model):
 company_branch = models.ForeignKey(
  CompanyBranch,
  on_delete=models.

Re: [Django] #34067: django.core.Paginator wrong query slicing

[Django]

#34067: django.core.Paginator wrong query slicing
-+-
 Reporter:  Hristo Trendafilov   |Owner:  nobody
 Type:  Bug  |   Status:  closed
Component:  Core (Other) |  Version:  3.2
 Severity:  Normal   |   Resolution:  needsinfo
 Keywords:   | Triage Stage:
  Paginator,slice,queryset   |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Mariusz Felisiak):

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


Comment:

 Thanks for the report, however `Paginator` works for me. I'm also not sure
 why you're using `_get_page()` which is a private undocumented API. I
 don't think you've explained the issue in enough detail to confirm a bug
 in Django. Please reopen the ticket if you can debug your issue and
 provide details about why and where Django is at fault. If you're having
 trouble in debugging, see TicketClosingReasons/UseSupportChannels for ways
 to get help.

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

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You received this message because you are subscribed to the Google Groups 
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Re: [Django] #34067: django.core.Paginator wrong query slicing

[Django]

#34067: django.core.Paginator wrong query slicing
-+-
 Reporter:  Hristo Trendafilov   |Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Core (Other) |  Version:  3.2
 Severity:  Normal   |   Resolution:
 Keywords:   | Triage Stage:
  Paginator,slice,queryset   |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Description changed by Hristo Trendafilov:

Old description:

> A have a ListView defined like so:
>
> {{{
> class AllPracticesListView(LoginRequiredMixin, PermissionRequiredMixin,
> ListView, ToolBoxFunctions):
> template_name = 'practice_list.html'
> model = Practice
> paginate_by = 6
> permission_required = 'customauth.access_practices'
>
> def get_queryset(self):
> qs = self.get_all_practices_by_user().order_by(
> 'company_branch__pk',
> 'practice_profile__personal_profile__last_name').prefetch_related('practice_profile')
>
> # method < get_all_practices_by_user > is a toolbox method that
> returns:
> #
> Practice.objects.filter(company_branch__owner=self.request.user).order_by('pk')
>
> return qs
>
> }}}
>
> Models are defined like so:
> {{{
>
>  class Practice(models.Model):
> company_branch = models.ForeignKey(
>  CompanyBranch,
>  on_delete=models.PROTECT,
>  related_name='practices',
> )
> # CompanyBranch model has an owner field which ForeignKey
> to the user model
>
> practice_profile = models.ForeignKey(
> PracticeProfile,
> on_delete=models.PROTECT,
> related_name='practices',
> )
>
> class PracticeProfile(models.Model):
> personal_profile = models.ForeignKey(
> PersonalProfile,
> on_delete=models.PROTECT,
> blank=True,
> null=True,
> )
> # PersonalProfile model has a field called <
> last_name >
> }}}
> Or schematically:
> {{{
> Practice object relations:
>   -> CompanyBranch
>   -> PracticeProfile
>   -> PersonalProfile /*NULLABLE RELATION/
>
> }}}
>
> When the code is run, the view does not display results correctly.
>
> I did like so to get the WRONG result:
> Added a breakpoint on  {{{Paginator._get_page}}} return statement
>
> Queryset is passed okay and is available in
> {{{Paginator.object_list}}}
>
> But in the args of {{{Paginator._get_page}}} the queryset is totally
> different than expected / should be a slice from the first six elements
> of {{{Paginator.object_list}}} /
>
> I have tried to add a breakpoint like so
> [[Image(https://imgur.com/SdaQUt6)]]
> Then I get this result [[Image(https://imgur.com/5zzLNV0)]].
>
> As you can see, PKs 1632, 1624, etc. are missing, objects are
> different/marked red and purple/, and are actually removed and never
> shown in the view.
>
> If you run slice manually at this point - everything is again fine
> [[Image(https://imgur.com/yvn8KMO)]]
> This happens only on NULL PersonalProfile objects.
>

> I did like so to get OKAY results:
>
> 1. Added a simple breakpoint is added on {{{Paginator.page}}} like so
> [[Image(https://imgur.com/d7J5BMZ)]] and that breakpoint is just run then
> the result is okay [[Image(https://imgur.com/ILDHAMN)]]
>
> 2. changed paginate_by to 10
>
> 3. changed {{{order_by}}} in {{{get_queryset}}} to {{{-pk}}}
>
> 4. call again the {{{page = paginator.page(page_number)}}}

New description:

 A have a ListView defined like so:

 {{{
 class AllPracticesListView(LoginRequiredMixin, PermissionRequiredMixin,
 ListView, ToolBoxFunctions):
 template_name = 'practice_list.html'
 model = Practice
 paginate_by = 6
 permission_required = 'customauth.access_practices'

 def get_queryset(self):
 qs = self.get_all_practices_by_user().order_by(
 'company_branch__pk',
 
'practice_profile__personal_profile__last_name').prefetch_related('practice_profile')

 # method < get_all_practices_by_user > is a toolbox method that
 returns:
 #
 Practice.objects.filter(company_branch__owner=self.request.user).order_by('pk')

 return qs

 }}}

 Models are defined like so:
 {{{

  class Practice(models.Model):
 company_branch = models.ForeignKey(
  CompanyBranch,
  on_delete=models.PROTECT,

Re: [Django] #34067: django.core.Paginator wrong query slicing

[Django]

#34067: django.core.Paginator wrong query slicing
-+-
 Reporter:  Hristo Trendafilov   |Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Core (Other) |  Version:  3.2
 Severity:  Normal   |   Resolution:
 Keywords:   | Triage Stage:
  Paginator,slice,queryset   |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Hristo Trendafilov):

 * Attachment "images2.zip" added.

 Other images

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

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Re: [Django] #34067: django.core.Paginator wrong query slicing

[Django]

#34067: django.core.Paginator wrong query slicing
-+-
 Reporter:  Hristo Trendafilov   |Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Core (Other) |  Version:  3.2
 Severity:  Normal   |   Resolution:
 Keywords:   | Triage Stage:
  Paginator,slice,queryset   |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Hristo Trendafilov):

 * Attachment "images.zip" added.

 Some of the images

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

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[Django] #34067: django.core.Paginator wrong query slicing

[Django]

#34067: django.core.Paginator wrong query slicing
-+-
   Reporter:  Hristo |  Owner:  nobody
  Trendafilov|
   Type:  Bug| Status:  new
  Component:  Core   |Version:  3.2
  (Other)|   Keywords:
   Severity:  Normal |  Paginator,slice,queryset
   Triage Stage: |  Has patch:  0
  Unreviewed |
Needs documentation:  0  |Needs tests:  0
Patch needs improvement:  0  |  Easy pickings:  0
  UI/UX:  0  |
-+-
 A have a ListView defined like so:

 {{{
 class AllPracticesListView(LoginRequiredMixin, PermissionRequiredMixin,
 ListView, ToolBoxFunctions):
 template_name = 'practice_list.html'
 model = Practice
 paginate_by = 6
 permission_required = 'customauth.access_practices'

 def get_queryset(self):
 qs = self.get_all_practices_by_user().order_by(
 'company_branch__pk',
 
'practice_profile__personal_profile__last_name').prefetch_related('practice_profile')

 # method < get_all_practices_by_user > is a toolbox method that
 returns:
 #
 Practice.objects.filter(company_branch__owner=self.request.user).order_by('pk')

 return qs

 }}}

 Models are defined like so:
 {{{

  class Practice(models.Model):
 company_branch = models.ForeignKey(
  CompanyBranch,
  on_delete=models.PROTECT,
  related_name='practices',
 )
 # CompanyBranch model has an owner field which ForeignKey
 to the user model

 practice_profile = models.ForeignKey(
 PracticeProfile,
 on_delete=models.PROTECT,
 related_name='practices',
 )

 class PracticeProfile(models.Model):
 personal_profile = models.ForeignKey(
 PersonalProfile,
 on_delete=models.PROTECT,
 blank=True,
 null=True,
 )
 # PersonalProfile model has a field called < last_name
 >
 }}}
 Or schematically:
 {{{
 Practice object relations:
   -> CompanyBranch
   -> PracticeProfile
   -> PersonalProfile /*NULLABLE RELATION/

 }}}

 When the code is run, the view does not display results correctly.

 I did like so to get the WRONG result:
 Added a breakpoint on  {{{Paginator._get_page}}} return statement

 Queryset is passed okay and is available in
 {{{Paginator.object_list}}}

 But in the args of {{{Paginator._get_page}}} the queryset is totally
 different than expected / should be a slice from the first six elements of
 {{{Paginator.object_list}}} /

 I have tried to add a breakpoint like so
 [[Image(https://imgur.com/SdaQUt6)]]
 Then I get this result [[Image(https://imgur.com/5zzLNV0)]].

 As you can see, PKs 1632, 1624, etc. are missing, objects are
 different/marked red and purple/, and are actually removed and never shown
 in the view.

 If you run slice manually at this point - everything is again fine
 [[Image(https://imgur.com/yvn8KMO)]]
 This happens only on NULL PersonalProfile objects.


 I did like so to get OKAY results:

 1. Added a simple breakpoint is added on {{{Paginator.page}}} like so
 [[Image(https://imgur.com/d7J5BMZ)]] and that breakpoint is just run then
 the result is okay [[Image(https://imgur.com/ILDHAMN)]]

 2. changed paginate_by to 10

 3. changed {{{order_by}}} in {{{get_queryset}}} to {{{-pk}}}

 4. call again the {{{page = paginator.page(page_number)}}}

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

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You received this message because you are subscribed to the Google Groups 
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