#24123: LookupError when rolling back migrations
---------------------------------+--------------------------------------
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
---------------------------------+--------------------------------------
Changes (by MarkusH):
* needs_docs: => 0
* needs_tests: => 0
* needs_better_patch: => 0
Old description:
> The `MigrationExecutor.migrate()` method generates the initial project
> state from the first migration that is being applied/unapplied. If this
> migration has no relations to other apps that are also being (un)applied,
> this can lead to `LookupError`s due to missing models:
>
> {{{#!python
> Traceback (most recent call last):
> File "/home/markus/Coding/django/django/apps/registry.py", line 148, in
> get_app_config
> return self.app_configs[app_label]
> KeyError: 'app_b'
>
> During handling of the above exception, another exception occurred:
>
> Traceback (most recent call last):
> File "/home/markus/Coding/django/django/db/migrations/state.py", line
> 181, in __init__
> model = self.get_model(lookup_model[0], lookup_model[1])
> File "/home/markus/Coding/django/django/apps/registry.py", line 202, in
> get_model
> return self.get_app_config(app_label).get_model(model_name.lower())
> File "/home/markus/Coding/django/django/apps/registry.py", line 150, in
> get_app_config
> raise LookupError("No installed app with label '%s'." % app_label)
> LookupError: No installed app with label 'app_b'.
>
> During handling of the above exception, another exception occurred:
>
> 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 75, in migrate
> state = self.unapply_migration(state, migration, fake=fake)
> File "/home/markus/Coding/django/django/db/migrations/executor.py",
> line 130, in unapply_migration
> state = migration.unapply(state, schema_editor)
> File "/home/markus/Coding/django/django/db/migrations/migration.py",
> line 157, in unapply
> operation.database_backwards(self.app_label, schema_editor,
> from_state, to_state)
> File
> "/home/markus/Coding/django/django/db/migrations/operations/models.py",
> line 62, in database_backwards
> model = from_state.apps.get_model(app_label, self.name)
> File "/home/markus/Coding/django/django/utils/functional.py", line 60,
> in __get__
> res = instance.__dict__[self.name] = self.func(instance)
> File "/home/markus/Coding/django/django/db/migrations/state.py", line
> 82, in apps
> return StateApps(self.real_apps, self.models)
> File "/home/markus/Coding/django/django/db/migrations/state.py", line
> 191, in __init__
> raise ValueError(msg.format(field=operations[0][1],
> model=lookup_model))
> ValueError: Lookup failed for model referenced by field app_a.A3.b2:
> app_b.B2
> }}}
>
> Given the attached migration dependencies, the backwards plan for
> `('app_a', None)` is
>
> {{{#!python
> [
> (<Migration app_c.0003_c3>, True),
> (<Migration app_a.0004_a4>, True),
> (<Migration app_a.0003_a3>, True),
> (<Migration app_c.0002_c2>, True),
> (<Migration app_b.0003_b3>, True),
> (<Migration app_b.0002_b2>, True),
> (<Migration app_a.0002_a2>, True),
> (<Migration app_a.0001_initial>, True)
> ]
> }}}
>
> The initial state generated from `app_c.0003_c3` is
>
> {{{
> app_a.a1:
> app_a.a2:
> app_c.c1:
> app_c.c2:
> }}}
>
> As one can see, there are no models of `app_b`, which eventually leads to
> an error when unapplying `app_1.0003_a3` which tries to look up model
> `app_b.B2`.
New description:
The `MigrationExecutor.migrate()` method generates the initial project
state from the first migration that is being applied/unapplied. If this
migration has no relations to other apps that are also being (un)applied,
this can lead to `LookupError`s due to missing models:
{{{#!python
Traceback (most recent call last):
File "/home/markus/Coding/django/django/apps/registry.py", line 148, in
get_app_config
return self.app_configs[app_label]
KeyError: 'app_b'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/home/markus/Coding/django/django/db/migrations/state.py", line
181, in __init__
model = self.get_model(lookup_model[0], lookup_model[1])
File "/home/markus/Coding/django/django/apps/registry.py", line 202, in
get_model
return self.get_app_config(app_label).get_model(model_name.lower())
File "/home/markus/Coding/django/django/apps/registry.py", line 150, in
get_app_config
raise LookupError("No installed app with label '%s'." % app_label)
LookupError: No installed app with label 'app_b'.
During handling of the above exception, another exception occurred:
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
75, in migrate
state = self.unapply_migration(state, migration, fake=fake)
File "/home/markus/Coding/django/django/db/migrations/executor.py", line
130, in unapply_migration
state = migration.unapply(state, schema_editor)
File "/home/markus/Coding/django/django/db/migrations/migration.py",
line 157, in unapply
operation.database_backwards(self.app_label, schema_editor,
from_state, to_state)
File
"/home/markus/Coding/django/django/db/migrations/operations/models.py",
line 62, in database_backwards
model = from_state.apps.get_model(app_label, self.name)
File "/home/markus/Coding/django/django/utils/functional.py", line 60,
in __get__
res = instance.__dict__[self.name] = self.func(instance)
File "/home/markus/Coding/django/django/db/migrations/state.py", line
82, in apps
return StateApps(self.real_apps, self.models)
File "/home/markus/Coding/django/django/db/migrations/state.py", line
191, in __init__
raise ValueError(msg.format(field=operations[0][1],
model=lookup_model))
ValueError: Lookup failed for model referenced by field app_a.A3.b2:
app_b.B2
}}}
Given the attached migration dependencies, the backwards plan for
`('app_a', None)` is
{{{
[
(<Migration app_c.0003_c3>, True),
(<Migration app_a.0004_a4>, True),
(<Migration app_a.0003_a3>, True),
(<Migration app_c.0002_c2>, True),
(<Migration app_b.0003_b3>, True),
(<Migration app_b.0002_b2>, True),
(<Migration app_a.0002_a2>, True),
(<Migration app_a.0001_initial>, True)
]
}}}
The initial state generated from `app_c.0003_c3` is
{{{
app_a.a1:
app_a.a2:
app_c.c1:
app_c.c2:
}}}
As one can see, there are no models of `app_b`, which eventually leads to
an error when unapplying `app_1.0003_a3` which tries to look up model
`app_b.B2`.
--
Comment:
I created a sample project to replicate the error:
https://github.com/MarkusH/django-ticket-triage/tree/bug24123
To replicate the above error for forwards migrations, take a clean
database and run
{{{#!console
$ python manage.py migrate app_b
Operations to perform:
Apply all migrations: app_b
Running migrations:
Applying app_a.0001_initial... OK
Applying app_a.0002_a2... OK
Applying app_b.0002_b2... OK
Applying app_b.0003_b3... OK
$ python manage.py migrate
Operations to perform:
Apply all migrations: app_a, app_c, app_b
Running migrations:
Applying app_c.0002_c2... OK
Applying app_a.0003_a3...
}}}
{{{#!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.apply_migration(state, migration, fake=fake)
File "/home/markus/Coding/django/django/db/migrations/executor.py", line
110, in apply_migration
state = migration.apply(state, schema_editor)
File "/home/markus/Coding/django/django/db/migrations/migration.py",
line 110, in apply
operation.database_forwards(self.app_label, schema_editor, old_state,
project_state)
File
"/home/markus/Coding/django/django/db/migrations/operations/models.py",
line 59, in database_forwards
schema_editor.create_model(model)
File "/home/markus/Coding/django/django/db/backends/schema.py", line
233, in create_model
definition, extra_params = self.column_sql(model, field)
File "/home/markus/Coding/django/django/db/backends/schema.py", line
132, in column_sql
db_params = field.db_parameters(connection=self.connection)
File "/home/markus/Coding/django/django/db/models/fields/related.py",
line 1996, in db_parameters
return {"type": self.db_type(connection), "check": []}
File "/home/markus/Coding/django/django/db/models/fields/related.py",
line 1987, in db_type
rel_field = self.related_field
File "/home/markus/Coding/django/django/db/models/fields/related.py",
line 1893, in related_field
return self.foreign_related_fields[0]
File "/home/markus/Coding/django/django/db/models/fields/related.py",
line 1627, 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 1614, in related_fields
self._related_fields = self.resolve_related_fields()
File "/home/markus/Coding/django/django/db/models/fields/related.py",
line 1599, in resolve_related_fields
raise ValueError('Related model %r cannot be resolved' % self.rel.to)
ValueError: Related model 'app_b.B2' cannot be resolved
}}}
The plan for the second migrate command is
{{{
[
(<Migration app_c.0002_c2>, False),
(<Migration app_a.0003_a3>, False),
(<Migration app_a.0004_a4>, False),
(<Migration app_c.0003_c3>, False)
]
}}}
The initial state is:
{{{
app_a.a1:
app_a.a2:
app_c.c1:
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/24123#comment:1>
Django <https://code.djangoproject.com/>
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