Re: [Django] #20535: Unnecessary join created for intermediate table between two M2M tables

[Django]

#20535: Unnecessary join created for intermediate table between two M2M tables
-+-
 Reporter:  German M. Bravo  |Owner:  (none)
 Type:  Bug  |   Status:  new
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:  1
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Can Sarıgöl):

 * status:  assigned => new
 * needs_better_patch:  0 => 1
 * owner:  Can Sarıgöl => (none)


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Re: [Django] #20535: Unnecessary join created for intermediate table between two M2M tables

[Django]

#20535: Unnecessary join created for intermediate table between two M2M tables
-+-
 Reporter:  German M. Bravo  |Owner:  Can
 |  Sarıgöl
 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 Can Sarıgöl):

 * status:  new => assigned
 * needs_better_patch:  1 => 0
 * owner:  nobody => Can Sarıgöl


Comment:

 [https://github.com/django/django/pull/11510 PR]

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Re: [Django] #20535: Unnecessary join created for intermediate table between two M2M tables

[Django]

#20535: Unnecessary join created for intermediate table between two M2M tables
-+-
 Reporter:  German M. Bravo  |Owner:  nobody
 Type:  Bug  |   Status:  new
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:  1
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Zach):

 * cc: Zach (added)


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Ticket URL: 
Django 
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Re: [Django] #20535: Unnecessary join created for intermediate table between two M2M tables

[Django]

#20535: Unnecessary join created for intermediate table between two M2M tables
-+-
 Reporter:  Kronuz   |Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:  Accepted
 Keywords:   |  Needs documentation:  0
Has patch:  1|  Patch needs improvement:  1
  Needs tests:  0|UI/UX:  0
Easy pickings:  0|
-+-
Changes (by akaariai):

 * needs_better_patch:  0 => 1
 * stage:  Unreviewed => Accepted


Comment:

 Yes, skipping non-necessary intermediate joins would be good.
 Unfortunately the added patch seems to introduce a lot of errors in the
 test suite.

 Maybe it would be better to do the trimming at compiler.get_from_clause()
 time? A join can be skipped if there are as many tables joining to it as
 its alias_refcount is, and every joined table can be joined directly to
 the "parent" table instead.

 Trimming joins before joins promotion is done is a bad idea. I am not sure
 if this applies to internal join trimming though.

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Re: [Django] #20535: Unnecessary join created for intermediate table between two M2M tables

[Django]

#20535: Unnecessary join created for intermediate table between two M2M tables
-+-
 Reporter:  Kronuz   |Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  master
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:
 Keywords:   |  Unreviewed
Has patch:  1|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Kronuz):

 * version:  1.5 => master


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Re: [Django] #20535: Unnecessary join created for intermediate table between two M2M tables

[Django]

#20535: Unnecessary join created for intermediate table between two M2M tables
-+-
 Reporter:  Kronuz   |Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  1.5
  (models, ORM)  |   Resolution:
 Severity:  Normal   | Triage Stage:
 Keywords:   |  Unreviewed
Has patch:  1|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Kronuz):

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


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Ticket URL: 
Django 
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[Django] #20535: Unnecessary join created for intermediate table between two M2M tables

[Django]

#20535: Unnecessary join created for intermediate table between two M2M tables
--+
 Reporter:  Kronuz|  Owner:  nobody
 Type:  Bug   | Status:  new
Component:  Database layer (models, ORM)  |Version:  1.5
 Severity:  Normal|   Keywords:
 Triage Stage:  Unreviewed|  Has patch:  0
Easy pickings:  0 |  UI/UX:  0
--+
 In this example:
 {{{#!python
 from django.db import models

 class Person(models.Model):
 name = models.CharField(max_length=128)
 friends = models.ManyToManyField('self', symmetrical=False,
 through='Relationship')

 def __unicode__(self):
 return self.name

 class Relationship(models.Model):
 from_person = models.ForeignKey(Person, related_name='idols')
 to_person = models.ForeignKey(Person, related_name='followers')
 }}}

 Example data for a test:
 {{{#!python
 ringo, _ = Person.objects.get_or_create(name="Ringo Starr")
 paul, _ = Person.objects.get_or_create(name="Paul McCartney")
 george, _ = Person.objects.get_or_create(name="George Harrison")
 john, _ = Person.objects.get_or_create(name="John Lennon")
 yoko, _ = Person.objects.get_or_create(name="Yoko Ono")

 Relationship.objects.get_or_create(from_person=ringo, to_person=paul)
 Relationship.objects.get_or_create(from_person=george, to_person=john)
 Relationship.objects.get_or_create(from_person=paul, to_person=ringo)
 Relationship.objects.get_or_create(from_person=paul, to_person=george)
 Relationship.objects.get_or_create(from_person=paul, to_person=john)
 Relationship.objects.get_or_create(from_person=john, to_person=paul)
 Relationship.objects.get_or_create(from_person=john, to_person=yoko)
 Relationship.objects.get_or_create(from_person=yoko, to_person=john)
 }}}

 Then doing (get idols of the idols of paul):
 {{{#!python
 print
 Relationship.objects.filter(from_person__followers__from_person=paul).query
 }}}

 This produces a join between `Relationship` and `Person`, then to
 `Relationship`, then to `Person`. The final join (to `Person`) gets
 trimmed by `trim_joins()` after the `setup_joins()` in
 `Query.add_filter()`. However, the unneeded join with `Person` (between
 the two joined `Relationship`) is not removed. This produces something
 like:
 {{{#!sql
 SELECT ... FROM relationship INNER JOIN person ON
 (relationship.from_person_id = person.id) INNER JOIN relationship T3 ON
 (person.id = T3.to_person_id) WHERE T3.from_person_id = 2;
 }}}

 When in fact all that would be needed is:
 {{{#!sql
 SELECT ... FROM relationship INNER JOIN relationship T3 ON
 (relationship.from_person_id = T3.to_person_id) WHERE T3.from_person_id =
 2
 }}}

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