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
24572	Migration plan may be broken when applying migrations on a clean database	Markus Holtermann	nobody	"1. ` python manage.py startapp a`
2. ` python manage.py startapp b`

It is important that app `a` is in alphabetically ordering before app `b`

3. Add both apps to `INSTALLED_APPS`

----

4. Add a model to app `a`:
{{{#!python
from django.db import models


class MyModel(models.Model):
    pass
}}}

5. Add a model to app `b`:
{{{#!python
from django.db import models


class MyModel(models.Model):
    pass
}}}

6. `python manage.py makemigrations`

----

7. Add a `ForeignKey` from `b.MyModel` to `a.MyModel`
{{{#!python
from django.db import models


class MyModel(models.Model):
    a = models.ForeignKey('a.MyModel', null=True)
}}}

8. `python manage.py makemigrations`

----

9. Remove the `ForeignKey` on `b.MyModel` to `a.MyModel`
{{{#!python
from django.db import models


class MyModel(models.Model):
    pass
}}}

10. `python manage.py makemigrations`

----

11. Remove `a.MyModel`
12. `python manage.py makemigrations`

----

13. `python manage.py showmigrations --plan -v 3`
{{{
[ ]  a.0001_initial
[ ]  a.0002_delete_mymodel ... (a.0001_initial)
[ ]  b.0001_initial
[ ]  b.0002_mymodel_a ... (a.0001_initial, b.0001_initial)
[ ]  b.0003_remove_mymodel_a ... (b.0002_mymodel_a)
}}}
14. `$ python manage.py migrate`
{{{
Operations to perform:
  Apply all migrations: a, b
Running migrations:
  Rendering model states... DONE
  Applying a.0001_initial... OK
  Applying a.0002_delete_mymodel... OK
  Applying b.0001_initial... OK
  Applying b.0002_mymodel_a...
}}}
{{{#!python
Traceback (most recent call last):
  File ""manage.py"", line 10, in <module>
    execute_from_command_line(sys.argv)
  File ""/home/markus/Coding/django/django/core/management/__init__.py"", line 330, in execute_from_command_line
    utility.execute()
  File ""/home/markus/Coding/django/django/core/management/__init__.py"", line 322, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File ""/home/markus/Coding/django/django/core/management/base.py"", line 347, in run_from_argv
    self.execute(*args, **cmd_options)
  File ""/home/markus/Coding/django/django/core/management/base.py"", line 398, in execute
    output = self.handle(*args, **options)
  File ""/home/markus/Coding/django/django/core/management/commands/migrate.py"", line 195, in handle
    executor.migrate(targets, plan, fake=fake, fake_initial=fake_initial)
  File ""/home/markus/Coding/django/django/db/migrations/executor.py"", line 110, in migrate
    self.apply_migration(states[migration], migration, fake=fake, fake_initial=fake_initial)
  File ""/home/markus/Coding/django/django/db/migrations/executor.py"", line 147, in apply_migration
    state = migration.apply(state, schema_editor)
  File ""/home/markus/Coding/django/django/db/migrations/migration.py"", line 118, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File ""/home/markus/Coding/django/django/db/migrations/operations/fields.py"", line 62, in database_forwards
    field,
  File ""/home/markus/Coding/django/django/db/backends/sqlite3/schema.py"", line 220, in add_field
    self._remake_table(model, create_fields=[field])
  File ""/home/markus/Coding/django/django/db/backends/sqlite3/schema.py"", line 179, in _remake_table
    self.create_model(temp_model)
  File ""/home/markus/Coding/django/django/db/backends/base/schema.py"", line 231, in create_model
    definition, extra_params = self.column_sql(model, field)
  File ""/home/markus/Coding/django/django/db/backends/base/schema.py"", line 130, in column_sql
    db_params = field.db_parameters(connection=self.connection)
  File ""/home/markus/Coding/django/django/db/models/fields/related.py"", line 2052, in db_parameters
    return {""type"": self.db_type(connection), ""check"": []}
  File ""/home/markus/Coding/django/django/db/models/fields/related.py"", line 2043, in db_type
    rel_field = self.target_field
  File ""/home/markus/Coding/django/django/db/models/fields/related.py"", line 1946, in target_field
    return self.foreign_related_fields[0]
  File ""/home/markus/Coding/django/django/db/models/fields/related.py"", line 1704, in foreign_related_fields
    return tuple(rhs_field for lhs_field, rhs_field in self.related_fields)
  File ""/home/markus/Coding/django/django/db/models/fields/related.py"", line 1691, in related_fields
    self._related_fields = self.resolve_related_fields()
  File ""/home/markus/Coding/django/django/db/models/fields/related.py"", line 1676, in resolve_related_fields
    raise ValueError('Related model %r cannot be resolved' % self.remote_field.model)
ValueError: Related model 'a.MyModel' cannot be resolved
}}}

----

The problem is that the migration `a.0002_delete_mymodel` doesn't have any information that it must  be applied after `b.0003_remove_mymodel_a` which in turn removes any references to `a.MyModel` again."	Bug	new	Migrations	dev	Normal			Florian Apolloner Shai Berger	Accepted	0	0	0	0	0	0