#22395 closed Bug (fixed)
Deleting a model and fields that relate to it results in ValueError: Related model '<app>.<model>' cannot be resolved
Reported by: | Stephen Burrows | Owned by: | nobody |
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Component: | Migrations | Version: | 2.0 |
Severity: | Normal | Keywords: | |
Cc: | Stephen Burrows | Triage Stage: | Accepted |
Has patch: | no | Needs documentation: | no |
Needs tests: | no | Patch needs improvement: | no |
Easy pickings: | no | UI/UX: | no |
Description
This seems to happen because a single migration is created which both deletes the model and the fields that reference it - but the fields are (sometimes?) deleted second, so the model is already "gone" by the time the migration gets that far.
Workaround is to move the field deletions up in the migrations file to *before* the model deletion.
Generated migration (relevant bits):
[...] class Migration(migrations.Migration): operations = [ migrations.DeleteModel( name='House', ), migrations.RemoveField( model_name='housingslot', name='house', ), migrations.RemoveField( model_name='person', name='house', ), ]
Traceback:
File "./manage.py", line 10, in <module> execute_from_command_line(sys.argv) File ".../django/django/core/management/__init__.py", line 427, in execute_from_command_line utility.execute() File ".../django/django/core/management/__init__.py", line 419, in execute self.fetch_command(subcommand).run_from_argv(self.argv) File ".../django/django/core/management/base.py", line 288, in run_from_argv self.execute(*args, **options.__dict__) File ".../django/django/core/management/base.py", line 337, in execute output = self.handle(*args, **options) File ".../django/django/core/management/commands/migrate.py", line 145, in handle executor.migrate(targets, plan, fake=options.get("fake", False)) File ".../django/django/db/migrations/executor.py", line 60, in migrate self.apply_migration(migration, fake=fake) File ".../django/django/db/migrations/executor.py", line 94, in apply_migration migration.apply(project_state, schema_editor) File ".../django/django/db/migrations/migration.py", line 97, in apply operation.database_forwards(self.app_label, schema_editor, project_state, new_state) File ".../django/django/db/migrations/operations/fields.py", line 36, in database_forwards field, File ".../django/django/db/backends/sqlite3/schema.py", line 117, in add_field self._remake_table(model, create_fields=[field]) File ".../django/django/db/backends/sqlite3/schema.py", line 84, in _remake_table self.create_model(temp_model) File ".../django/django/db/backends/schema.py", line 191, in create_model definition, extra_params = self.column_sql(model, field) File ".../django/django/db/backends/schema.py", line 108, in column_sql db_params = field.db_parameters(connection=self.connection) File ".../django/django/db/models/fields/related.py", line 1758, in db_parameters return {"type": self.db_type(connection), "check": []} File ".../django/django/db/models/fields/related.py", line 1749, in db_type rel_field = self.related_field File ".../django/django/db/models/fields/related.py", line 1655, in related_field return self.foreign_related_fields[0] File ".../django/django/db/models/fields/related.py", line 1414, in foreign_related_fields return tuple(rhs_field for lhs_field, rhs_field in self.related_fields) File ".../django/django/db/models/fields/related.py", line 1401, in related_fields self._related_fields = self.resolve_related_fields() File ".../django/django/db/models/fields/related.py", line 1386, in resolve_related_fields raise ValueError('Related model %r cannot be resolved' % self.rel.to) ValueError: Related model 'brambling.House' cannot be resolved
Change History (10)
comment:1 by , 11 years ago
Triage Stage: | Unreviewed → Accepted |
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comment:3 by , 11 years ago
This looks potentially related to the root cause of #22397 and it's possible my work on that bug will affect this one.
comment:4 by , 11 years ago
I'm technically running 1.7.X, not the 1.7b1 tag. So it could be a newly-introduced bug. I'll test.
The project I'm using is https://github.com/littleweaver/django-brambling - but we worked around this a while ago.
I'll pull the latest 1.7.X and see if it's been fixed.
comment:5 by , 11 years ago
I can't reproduce this exact bug any more in 1.7.X while migrating forward, but it does still show up in reverse migrations.
It does look like this will probably be resolved by #22397.
comment:6 by , 11 years ago
@melinath, could you check if this is still an issue as the ticket you referenced above has been resolved? If it still is, some steps to reproduce would be helpful, as it will be easier than reversing them from the details you've provided.
comment:7 by , 11 years ago
@timo: Yeah, seems fixed. But to find that out I have to checkout a6ecd5dbb34249f756a337c359eef1e8d78dc01e (to avoid #22563) then checkout stable/1.7.x to make the migration. So... yeah, it has been fixed, probably :-p
comment:8 by , 10 years ago
Resolution: | → fixed |
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Status: | new → closed |
comment:9 by , 6 years ago
Resolution: | fixed |
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Status: | closed → new |
Version: | 1.7-beta-1 → 2.0 |
I ran into this bug today using Django 2.0.8, so I think it can still crop up. It's an easy workaround, as mentioned above, but happening nonetheless. I'll try to find some time to write a test case to reproduce it.
comment:10 by , 6 years ago
Resolution: | → fixed |
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Status: | new → closed |
Dan, it is possible that the migrations were generated before the issue was fixed?
If it's the case the bug will be present on any version of Django as long as the migration operations are not re-ordered manually.
Please file a new ticket referencing this one if you manage to reproduce a makemigrations
call that orders operations inappropriately.
I couldn't reproduce the bug. Not on stable (f004374) and not on the 1.7b1 tag. I tried the following:
https://github.com/Ofir-Purple/django/tree/testing-22395
https://github.com/Ofir-Purple/django/tree/testing-22395-on-1.7b1
And tried to create a project with 2 related fields. I made sure that the migration's operations were: First delete the model, then the related fields; But to no avail. The migrations worked fine.
Do you have a link to a full project that reproduces the bug?