id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
22605	Impossible to delete two models with a M2M field	Andrew Godwin	Andrew Godwin	"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
}}}"	Bug	closed	Migrations	1.7-beta-2	Release blocker	fixed			Accepted	0	0	0	0	0	0