Re: [Django] #15200: ManyToManyField combined with "|" leads to trouble

[Django]

#15200: ManyToManyField combined with "|" leads to trouble
-+--
   Reporter:  vanschelven| Owner:  nobody
 Status:  closed | Milestone:
  Component:  Uncategorized  |   Version:  1.2   
 Resolution:  wontfix|  Keywords:
   Triage Stage:  Unreviewed | Has patch:  0 
Needs documentation:  0  |   Needs tests:  0 
Patch needs improvement:  0  |  
-+--

Comment (by vanschelven):

 Hmmm... I guess you're talking about the following snippet:


 By default, a !QuerySet will not eliminate duplicate rows. In practice,
 this is rarely a problem, because simple queries such as
 Blog.objects.all() don't introduce the possibility of duplicate result
 rows. However, if your query spans multiple tables, it's possible to get
 duplicate results when a !QuerySet is evaluated. That's when you'd use
 distinct().


 IMHO this kind of leakiness is the worst kind (it happens only very
 rarely, and may happen intermittently depending on your data). Anyway I'm
 letting it rest for now.

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Re: [Django] #15200: ManyToManyField combined with "|" leads to trouble

[Django]

#15200: ManyToManyField combined with "|" leads to trouble
-+--
   Reporter:  vanschelven| Owner:  nobody
 Status:  closed | Milestone:
  Component:  Uncategorized  |   Version:  1.2   
 Resolution:  wontfix|  Keywords:
   Triage Stage:  Unreviewed | Has patch:  0 
Needs documentation:  0  |   Needs tests:  0 
Patch needs improvement:  0  |  
-+--
Changes (by russellm):

  * status:  reopened => closed
  * resolution:  => wontfix


Comment:

 Yes, but the issue is that it's a *documented* leaky abstraction, and one
 that is very difficult to avoid without imposing a large computational
 overhead -- which is why the leaky abstraction exists.

 Trust me -- we've thought about this. That's why it's a documented leaky
 abstraction. If you want to advocate for a different, less leaky
 interpretation, feel free to raise the issue on django dev. But be warned:
 you're not going to get much attention unless you come armed with an
 actual solution in the form of working code, or, at the very least, a
 general SQL solution to the problem.

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Re: [Django] #15200: ManyToManyField combined with "|" leads to trouble

[Django]

#15200: ManyToManyField combined with "|" leads to trouble
-+--
   Reporter:  vanschelven| Owner:  nobody
 Status:  reopened   | Milestone:
  Component:  Uncategorized  |   Version:  1.2   
 Resolution: |  Keywords:
   Triage Stage:  Unreviewed | Has patch:  0 
Needs documentation:  0  |   Needs tests:  0 
Patch needs improvement:  0  |  
-+--
Changes (by vanschelven):

  * status:  closed => reopened
  * resolution:  invalid =>


Comment:

 Yes I'm indeed referring to the fact that there's a duplicate in the
 results. IMHO "abstraction leakage" is a bug and though it may be overcome
 with distinct() I think this is a little more fundamental.

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Re: [Django] #15200: ManyToManyField combined with "|" leads to trouble

[Django]

#15200: ManyToManyField combined with "|" leads to trouble
-+--
   Reporter:  vanschelven| Owner:  nobody
 Status:  closed | Milestone:
  Component:  Uncategorized  |   Version:  1.2   
 Resolution:  invalid|  Keywords:
   Triage Stage:  Unreviewed | Has patch:  0 
Needs documentation:  0  |   Needs tests:  0 
Patch needs improvement:  0  |  
-+--
Changes (by anonymous):

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


Comment:

 Are you referring to the fact that there is a duplicate in the results? If
 this is the case, then this is a case of abstraction leakage, overcome
 with the use of
 
[http://docs.djangoproject.com/en/1.2/ref/models/querysets/#django.db.models.QuerySet.distinct
 distinct()]

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Re: [Django] #15200: ManyToManyField combined with "|" leads to trouble

[Django]

#15200: ManyToManyField combined with "|" leads to trouble
-+--
   Reporter:  vanschelven| Owner:  nobody
 Status:  new| Milestone:
  Component:  Uncategorized  |   Version:  1.2   
 Resolution: |  Keywords:
   Triage Stage:  Unreviewed | Has patch:  0 
Needs documentation:  0  |   Needs tests:  0 
Patch needs improvement:  0  |  
-+--
Changes (by vanschelven):

 * cc: vanschelven (added)
  * needs_docs:  => 0
  * needs_tests:  => 0
  * needs_better_patch:  => 0


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[Django] #15200: ManyToManyField combined with "|" leads to trouble

[Django]

#15200: ManyToManyField combined with "|" leads to trouble
---+
 Reporter:  vanschelven|  Owner:  nobody
   Status:  new|  Milestone:
Component:  Uncategorized  |Version:  1.2   
 Keywords: |   Triage Stage:  Unreviewed
Has patch:  0  |  
---+
 !ManyToManyField combined with "|" leads to trouble.

 Specifically, the outer join that appears to be constructed for manytomany
 field lookups is not well cleaned up with where statements once an "or"
 ("|") is used.

 {{{
 $ cat theapp/models.py
 from django.db import models

 class AnObject(models.Model):
 nr = models.IntegerField()

 class HasRef(models.Model):
 obj = models.ManyToManyField(AnObject)
 field = models.IntegerField()
 }}}

 {{{
 >>> from theapp.models import *
 >>> one = AnObject.objects.create(nr=1)
 >>> two = AnObject.objects.create(nr=2)
 >>> reffer = HasRef.objects.create(field=1)
 >>> reffer.obj.add(one)
 >>> reffer.obj.add(two)
 >>> HasRef.objects.all().filter(field=1)
 []
 >>> HasRef.objects.all().filter(obj=one)
 []
 >>> HasRef.objects.all().filter(models.Q(field=1) | models.Q(obj=one))
 [, ]
 >>> [o.pk for o in HasRef.objects.all().filter(models.Q(field=1) |
 models.Q(obj=one))]
 [1L, 1L]
 }}}

 I don't have the time right now to come up with tests proper, or a patch.
 The problem is real though...

 My workaround:

 {{{
 >>> HasRef.objects.all().filter(models.Q(field=1) |
 models.Q(obj=one)).annotate(models.Count("id"))
 }}}

 The generated query (without workaround)
 {{{
 >>> print HasRef.objects.all().filter(models.Q(field=1) |
 models.Q(obj=AnObject.objects.get(nr=1))).query
 SELECT `theapp_hasref`.`id`, `theapp_hasref`.`field` FROM `theapp_hasref`
 LEFT OUTER JOIN `theapp_hasref_obj` ON (`theapp_hasref`.`id` =
 `theapp_hasref_obj`.`hasref_id`) WHERE (`theapp_hasref`.`field` = 1  OR
 `theapp_hasref_obj`.`anobject_id` = 1 )
 }}}
 {{{

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