#22605: Impossible to delete two models with a M2M field
---------------------------------+--------------------
Reporter: andrewgodwin | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: master
Severity: Release blocker | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
---------------------------------+--------------------
In playing around with some test code, I removed the following models and
made a migration to delete them:
{{{
class Table1(models.Model):
pass
class Table2(models.Model):
m2m = models.ManyToManyField(Table1, through='M2M', blank=True)
class M2M(models.Model):
t1 = models.ForeignKey(Table1, related_name='+')
t2 = models.ForeignKey(Table2, related_name='+')
}}}
The resulting deletion is impossible, as Table2 and M2M have a circular
dependency and the "lookup failed" code means you can never get past the
migration with errors such as:
{{{
Applying polls.0005_auto_20140509_0258...Traceback (most recent call
last):
File "./manage.py", line 10, in <module>
execute_from_command_line(sys.argv)
File "/home/andrew/Programs/Django/django/core/management/__init__.py",
line 427, in execute_from_command_line
utility.execute()
File "/home/andrew/Programs/Django/django/core/management/__init__.py",
line 419, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/home/andrew/Programs/Django/django/core/management/base.py", line
288, in run_from_argv
self.execute(*args, **options.__dict__)
File "/home/andrew/Programs/Django/django/core/management/base.py", line
337, in execute
output = self.handle(*args, **options)
File
"/home/andrew/Programs/Django/django/core/management/commands/migrate.py",
line 146, in handle
executor.migrate(targets, plan, fake=options.get("fake", False))
File "/home/andrew/Programs/Django/django/db/migrations/executor.py",
line 62, in migrate
self.apply_migration(migration, fake=fake)
File "/home/andrew/Programs/Django/django/db/migrations/executor.py",
line 96, in apply_migration
migration.apply(project_state, schema_editor)
File "/home/andrew/Programs/Django/django/db/migrations/migration.py",
line 107, in apply
operation.database_forwards(self.app_label, schema_editor,
project_state, new_state)
File
"/home/andrew/Programs/Django/django/db/migrations/operations/models.py",
line 80, in database_forwards
apps = from_state.render()
File "/home/andrew/Programs/Django/django/db/migrations/state.py", line
94, in render
extra_message=extra_message,
ValueError: Lookup failed for model referenced by field polls.Table2.m2m:
polls.M2M
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/22605>
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 [email protected].
To post to this group, send email to [email protected].
To view this discussion on the web visit
https://groups.google.com/d/msgid/django-updates/055.d02f458e442b07b525d08981a428fbfc%40djangoproject.com.
For more options, visit https://groups.google.com/d/optout.
