#33209: ManyToManyField.add() doesn't respect a unique constraint in
intermediate
table
-------------------------------------+-------------------------------------
Reporter: Yuta Okamoto | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 3.1
(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 Yuta Okamoto:
Old description:
> I added the following `Company` and `Member` models, and `CompanyMember`
> as their intermediate table with a unique constraint including `role`
> field in addition to `through_fields`.
>
> {{{#!python
> from django.db import models
>
> class Company(models.Model):
> pass
>
> class Member(models.Model):
> companies = models.ManyToManyField(Company, through='CompanyMember',
> related_name='members')
>
> class CompanyMember:
> company = models.ForeignKey(Company, on_delete=models.CASCADE)
> member = models.ForeignKey(Member, on_delete=models.CASCADE)
> role = models.SmallIntegerField()
>
> class Meta:
> constraints = [
> models.UniqueConstraint(fields=['company', 'member', 'role'],
> name='company_member_role'),
> ]
> }}}
>
> In this situation, `company.members.add()` fails to add existing member
> with different role specified via `through_defaults`.
>
> {{{#!python
> company = Company.objects.create()
> member = Member.objects.create()
>
> company.members.add(member, through_defaults={'role': 1})
> assert company.members.through.objects.all().count() == 1
>
> company.members.add(member, through_defaults={'role': 2})
> assert company.members.through.objects.all().count() == 2 # fails
> }}}
>
> We need to workaround by adding the relation to the intermediate table
> directly.
>
> {{{#!python
> company.members.through.objects.create(
> company.members.through(company=company, member=member, role=2)
> )
> }}}
New description:
I added the following `Company` and `Member` models, and `CompanyMember`
as their intermediate table with a unique constraint including `role`
field in addition to `through_fields`.
{{{#!python
from django.db import models
class Company(models.Model):
pass
class Member(models.Model):
companies = models.ManyToManyField(Company, through='CompanyMember',
related_name='members')
class CompanyMember:
company = models.ForeignKey(Company, on_delete=models.CASCADE)
member = models.ForeignKey(Member, on_delete=models.CASCADE)
role = models.SmallIntegerField()
class Meta:
constraints = [
models.UniqueConstraint(fields=['company', 'member', 'role'],
name='company_member_role'),
]
}}}
In this situation, `company.members.add()` silently fails to add existing
member with different role specified via `through_defaults`.
{{{#!python
company = Company.objects.create()
member = Member.objects.create()
company.members.add(member, through_defaults={'role': 1})
assert company.members.through.objects.all().count() == 1
company.members.add(member, through_defaults={'role': 2})
assert company.members.through.objects.all().count() == 2 # fails
}}}
We need to workaround by adding the relation to the intermediate table
directly.
{{{#!python
company.members.through.objects.create(
company.members.through(company=company, member=member, role=2)
)
}}}
--
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Ticket URL: <https://code.djangoproject.com/ticket/33209#comment:3>
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