#31581: Queryset bug when using Q()? -- doubles up the counts by doing an extra
join
-------------------------------------+-------------------------------------
     Reporter:  Javier Buzzi         |                    Owner:  nobody
         Type:  Bug                  |                   Status:  new
    Component:  Database layer       |                  Version:  3.0
  (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
-------------------------------------+-------------------------------------
Description changed by Javier Buzzi:

Old description:

> I ran this on all the "recent" versions of python and i see the issue on
> all of them. At this point, im not 100% sure if it is a problem or not, i
> ran across this trying to show some counts in the Admin that had some
> search_fields that traversed the model backwards and forwards in order to
> match the thing properly.
>
> This "bug" can be seen from 1.11-3.0. Havent checked 3.1
>
> This is my mocked models of the issue:
>
> {{{
> class ModelA(models.Model):
>     somecriteria = models.CharField(max_length=50)
>

> class ModelC(models.Model):
>     unimportant = models.CharField(max_length=50)
>

> class ModelB(models.Model):
>     somerelation = models.ForeignKey(ModelA, on_delete=models.CASCADE)
>     m2m = models.ManyToManyField(
>         ModelC,
>         through='ModelBC'
>     )
>

> class ModelBC(models.Model):
>     b = models.ForeignKey(ModelB, on_delete=models.CASCADE)
>     c = models.ForeignKey(ModelC, on_delete=models.CASCADE)
> }}}
>
> The "bug" is shown when i do:
>
> {{{
> queryset =
> ModelB.objects.select_related('a').annotate(num_c=Count('m2m__id')).values('num_c')
> queryset = queryset.filter(Q(modelbc__c__unimportant='1') |
> Q(somerelation__somecriteria='1'))
> }}}
>
> When i do:
>
> {{{
> queryset =
> ModelB.objects.select_related('a').annotate(num_c=Count('m2m__id')).values('num_c')
> queryset = queryset.filter(modelbc__c__unimportant='1',
> somerelation__somecriteria='1')
> }}}
>
> it works as expected.
>
> My testing arena can be found here:
> https://gist.github.com/kingbuzzman/9fe5470e31a421aa88b2a64e5447e147  see
> the comments, for the way to run it.

New description:

 I ran this on all the "recent" versions of python and i see the issue on
 all of them. At this point, im not 100% sure if it is a problem or not, i
 ran across this trying to show some counts in the Admin that had some
 search_fields that traversed the model backwards and forwards in order to
 match the thing properly.

 This "bug" can be seen from 1.11-3.0. Haven't checked 3.1 because i cant
 find it in pip.

 This is my mocked models of the issue:

 {{{
 class ModelA(models.Model):
     somecriteria = models.CharField(max_length=50)


 class ModelC(models.Model):
     unimportant = models.CharField(max_length=50)


 class ModelB(models.Model):
     somerelation = models.ForeignKey(ModelA, on_delete=models.CASCADE)
     m2m = models.ManyToManyField(
         ModelC,
         through='ModelBC'
     )


 class ModelBC(models.Model):
     b = models.ForeignKey(ModelB, on_delete=models.CASCADE)
     c = models.ForeignKey(ModelC, on_delete=models.CASCADE)
 }}}

 The "bug" is shown when i do:

 {{{
 queryset =
 
ModelB.objects.select_related('a').annotate(num_c=Count('m2m__id')).values('num_c')
 queryset = queryset.filter(Q(modelbc__c__unimportant='1') |
 Q(somerelation__somecriteria='1'))
 }}}

 When i do:

 {{{
 queryset =
 
ModelB.objects.select_related('a').annotate(num_c=Count('m2m__id')).values('num_c')
 queryset = queryset.filter(modelbc__c__unimportant='1',
 somerelation__somecriteria='1')
 }}}

 it works as expected.

 My testing arena can be found here:
 https://gist.github.com/kingbuzzman/9fe5470e31a421aa88b2a64e5447e147  see
 the comments, for the way to run it.

--

-- 
Ticket URL: <https://code.djangoproject.com/ticket/31581#comment:3>
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