#33209: ManyToManyField.add() doesn't respect a unique constraint in
intermediate
table
-------------------------------------+-------------------------------------
Reporter: okapies | Owner: nobody
Type: Bug | Status: new
Component: Database | Version: 3.1
layer (models, ORM) |
Severity: Normal | Keywords:
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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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.
{{{#!python
company = Company.objects.create()
member = Member.objects.create()
company.members.add(member, through_defaults={'role': 1})
assert Company.objects.all().count() == 1
company.members.add(member, through_defaults={'role': 2})
assert Company.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)
)
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/33209>
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