#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()` 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) > ) > }}} 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', through_fields=('company', 'member'), 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) ) }}} -- -- Ticket URL: <https://code.djangoproject.com/ticket/33209#comment:4> Django <https://code.djangoproject.com/> The Web framework for perfectionists with deadlines. -- You received this message because you are subscribed to the Google Groups "Django updates" group. To unsubscribe from this group and stop receiving emails from it, send an email to django-updates+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/django-updates/065.2bc13d9bc705656f5efd7c17634e23fa%40djangoproject.com.