[Django] #25486: ORM generating incorrect query for through-model on <RelatedManager>.all()

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Sep 30, 2015, 5:09:38 PM9/30/15

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#25486: ORM generating incorrect query for through-model on <RelatedManager>.all()
----------------------------------------------+--------------------
Reporter: pembo13 | Owner: nobody
Type: Bug | Status: new
Component: Database layer (models, ORM) | Version: 1.8
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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I have a through-model which itself has a through model (because it needs
a many-to-many relationship). The problem comes when i try to get related
mode through this many-to-many relationship. The ORM generates the WHERE
clause on the wrong field (the pk, instead of the fk).

{{{
#!sql
-- generated sql
SELECT "core_role"."id", "core_role"."name"
FROM "core_role"
INNER JOIN "core_dealercontactrole" ON ( "core_role"."id" =
"core_dealercontactrole"."role_id" )
WHERE "core_dealercontactrole"."id" = 8743
ORDER BY "core_role"."name" ASC

-- corrected sql
SELECT "core_role"."id", "core_role"."name"
FROM "core_role"
INNER JOIN "core_dealercontactrole" ON ( "core_role"."id" =
"core_dealercontactrole"."role_id" )
WHERE "core_dealercontactrole"."dealercontact_id" = 8743
ORDER BY "core_role"."name" ASC
}}}

The code that generated the query:

{{{
#!python
dc = DealerContact.objects.get(id=8743)
>>> unicode(dc.roles.all().query)
u'SELECT "core_role"."id", "core_role"."name" FROM "core_role" INNER JOIN
"core_dealercontactrole" ON ( "core_role"."id" =
"core_dealercontactrole"."role_id" ) WHERE "core_dealercontactrole"."id" =
8743 ORDER BY "core_role"."name" ASC'
}}}

Here are the models (with superfluous fields removed):

{{{
#!python
class Contact(models.Model):

first_name = models.CharField(blank=True, max_length=50)
last_name = models.CharField(blank=True, max_length=50)

class Meta:
ordering = ('last_name','first_name')

pass

class Dealer(models.Model):

contacts = models.ManyToManyField('Contact',
through='DealerContact', related_name='dealers')

name = models.CharField(db_index=True, max_length=250)

pass

class DealerContact(models.Model):

dealer = models.ForeignKey('Dealer',
related_name='dealercontacts+', on_delete=models.CASCADE)
contact = models.ForeignKey('Contact', related_name='+',
on_delete=models.CASCADE)
roles = models.ManyToManyField('Role',
through='DealerContactRole', related_name='+')

class Meta:
unique_together = ('dealer','contact')

pass

class DealerContactRole(models.Model):

dealercontact = models.ForeignKey('DealerContact',
related_name='+', on_delete=models.CASCADE)
role = models.ForeignKey('Role', related_name='+')

class Meta:
unique_together = ('dealercontact','role')

pass

class Role(models.Model):

name = models.CharField(db_index=True, max_length=100)

class Meta:
ordering = ('name',)

pass
}}}

--
Ticket URL: <https://code.djangoproject.com/ticket/25486>
Django <https://code.djangoproject.com/>
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Django

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Sep 30, 2015, 6:22:24 PM9/30/15

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#25486: ORM generating incorrect query for through-model on <RelatedManager>.all()

Easy pickings: 0 | UI/UX: 0

-------------------------------------+-------------------------------------
Changes (by timgraham):

* status: new => closed
* needs_better_patch: => 0
* needs_tests: => 0
* needs_docs: => 0
* resolution: => duplicate

Old description:

New description:

class Dealer(models.Model):

contacts = models.ManyToManyField('Contact', through='DealerContact',
related_name='dealers')
name = models.CharField(db_index=True, max_length=250)

class DealerContact(models.Model):

dealer = models.ForeignKey('Dealer', related_name='dealercontacts+',
on_delete=models.CASCADE)
contact = models.ForeignKey('Contact', related_name='+',
on_delete=models.CASCADE)
roles = models.ManyToManyField('Role', through='DealerContactRole',
related_name='+')

class Meta:
unique_together = ('dealer', 'contact')

class DealerContactRole(models.Model):

dealercontact = models.ForeignKey('DealerContact', related_name='+',
on_delete=models.CASCADE)
role = models.ForeignKey('Role', related_name='+')

class Meta:
unique_together = ('dealercontact', 'role')

class Role(models.Model):
name = models.CharField(db_index=True, max_length=100)

class Meta:
ordering = ('name',)
}}}

Comment:

This seems to be a regression in 1.8 and a duplicate of #24505 (bisected
to fb48eb05816b1ac87d58696cdfe48be18c901f16 and fixed subsequently fixed
in 4ee08958f154594b538207a53c1d457687b3f7ae). I'll backport that fix to
1.8.