#24110: Unapplying a migration has side-effects on the ProjectState passed to
the
method
---------------------------------+--------------------------------------
Reporter: MarkusH | Owner: MarkusH
Type: Bug | Status: new
Component: Migrations | Version: master
Severity: Release blocker | 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 MarkusH:
Old description:
> In some edge cases, I think, related models in the migration state are
> referenced via strings rather than `__fake__` models. This is related to
> #23745 and 1aa3e09c2043c88a760e8b73fb95dc8f1ffef50e
>
> {{{#!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 338, in execute_from_command_line
> utility.execute()
> File "/home/markus/Coding/django/django/core/management/__init__.py",
> line 330, in execute
> self.fetch_command(subcommand).run_from_argv(self.argv)
> File "/home/markus/Coding/django/django/core/management/base.py", line
> 390, in run_from_argv
> self.execute(*args, **cmd_options)
> File "/home/markus/Coding/django/django/core/management/base.py", line
> 444, in execute
> output = self.handle(*args, **options)
> File
> "/home/markus/Coding/django/django/core/management/commands/migrate.py",
> line 213, in handle
> executor.migrate(targets, plan, fake=options.get("fake", False))
> File "/home/markus/Coding/django/django/db/migrations/executor.py",
> line 73, in migrate
> state = self.unapply_migration(state, migration, fake=fake)
> File "/home/markus/Coding/django/django/db/migrations/executor.py",
> line 127, in unapply_migration
> state = migration.unapply(state, schema_editor)
> File "/home/markus/Coding/django/django/db/migrations/migration.py",
> line 135, in unapply
> operation.state_forwards(self.app_label, project_state)
> File
> "/home/markus/Coding/django/django/db/migrations/operations/models.py",
> line 53, in state_forwards
> list(self.managers),
> File "/home/markus/Coding/django/django/db/migrations/state.py", line
> 39, in add_model
> self.reload_model(app_label, model_name)
> File "/home/markus/Coding/django/django/db/migrations/state.py", line
> 61, in reload_model
> self._reload_one_model(rel_model._meta.app_label,
> rel_model._meta.model_name)
> AttributeError: 'str' object has no attribute '_meta'
> }}}
>
> I've yet to figure out when this is happening exactly.
New description:
`django.db.migrations.migration.Migration.unapply()` accepts an argument
`state` that represents the project state right before the migration is
applied. The current implementation alters this state when building the
intermediate states to which each operation rolls back, instead of using a
copy. This side effect results in errors where e.g. a model can exists in
the state, but its gone from the database.
{{{#!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 338, in execute_from_command_line
utility.execute()
File "/home/markus/Coding/django/django/core/management/__init__.py",
line 330, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/home/markus/Coding/django/django/core/management/base.py", line
390, in run_from_argv
self.execute(*args, **cmd_options)
File "/home/markus/Coding/django/django/core/management/base.py", line
444, in execute
output = self.handle(*args, **options)
File
"/home/markus/Coding/django/django/core/management/commands/migrate.py",
line 213, in handle
executor.migrate(targets, plan, fake=options.get("fake", False))
File "/home/markus/Coding/django/django/db/migrations/executor.py", line
73, in migrate
state = self.unapply_migration(state, migration, fake=fake)
File "/home/markus/Coding/django/django/db/migrations/executor.py", line
127, in unapply_migration
state = migration.unapply(state, schema_editor)
File "/home/markus/Coding/django/django/db/migrations/migration.py",
line 135, in unapply
operation.state_forwards(self.app_label, project_state)
File
"/home/markus/Coding/django/django/db/migrations/operations/models.py",
line 53, in state_forwards
list(self.managers),
File "/home/markus/Coding/django/django/db/migrations/state.py", line
39, in add_model
self.reload_model(app_label, model_name)
File "/home/markus/Coding/django/django/db/migrations/state.py", line
61, in reload_model
self._reload_one_model(rel_model._meta.app_label,
rel_model._meta.model_name)
AttributeError: 'str' object has no attribute '_meta'
}}}
--
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Ticket URL: <https://code.djangoproject.com/ticket/24110#comment:2>
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