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 24627 Race condition like error in migration Martin Häcker nobody "Hi there, I'm having a strange error in some migrations. Let me describe: At first I had several migrations, one renamed a model process.ProcessDef to process.ProcessDefinition, then a later one would rename a field on that model. {{{ migrations.RenameModel( old_name='ProcInstance', new_name='ProcessInstance', ), migrations.RenameField( model_name='processinstance', old_name='status', new_name='runstatus', ), }}} This creates a stack trace that looks like this: {{{ File ""./manage.py"", line 10, in execute_from_command_line(sys.argv) File ""/Users/dwt/.virtualenvs/pycess/lib/python3.4/site-packages/django/core/management/__init__.py"", line 338, in execute_from_command_line utility.execute() File ""/Users/dwt/.virtualenvs/pycess/lib/python3.4/site-packages/django/core/management/__init__.py"", line 330, in execute self.fetch_command(subcommand).run_from_argv(self.argv) File ""/Users/dwt/.virtualenvs/pycess/lib/python3.4/site-packages/django/core/management/base.py"", line 390, in run_from_argv self.execute(*args, **cmd_options) File ""/Users/dwt/.virtualenvs/pycess/lib/python3.4/site-packages/django/core/management/base.py"", line 441, in execute output = self.handle(*args, **options) File ""/Users/dwt/.virtualenvs/pycess/lib/python3.4/site-packages/django/core/management/commands/migrate.py"", line 221, in handle executor.migrate(targets, plan, fake=fake, fake_initial=fake_initial) File ""/Users/dwt/.virtualenvs/pycess/lib/python3.4/site-packages/django/db/migrations/executor.py"", line 110, in migrate self.apply_migration(states[migration], migration, fake=fake, fake_initial=fake_initial) File ""/Users/dwt/.virtualenvs/pycess/lib/python3.4/site-packages/django/db/migrations/executor.py"", line 147, in apply_migration state = migration.apply(state, schema_editor) File ""/Users/dwt/.virtualenvs/pycess/lib/python3.4/site-packages/django/db/migrations/migration.py"", line 115, in apply operation.database_forwards(self.app_label, schema_editor, old_state, project_state) File ""/Users/dwt/.virtualenvs/pycess/lib/python3.4/site-packages/django/db/migrations/operations/fields.py"", line 275, in database_forwards to_model._meta.get_field(self.new_name), File ""/Users/dwt/.virtualenvs/pycess/lib/python3.4/site-packages/django/db/backends/base/schema.py"", line 484, in alter_field old_db_params, new_db_params, strict) File ""/Users/dwt/.virtualenvs/pycess/lib/python3.4/site-packages/django/db/backends/sqlite3/schema.py"", line 200, in _alter_field self._remake_table(model, alter_fields=[(old_field, new_field)]) File ""/Users/dwt/.virtualenvs/pycess/lib/python3.4/site-packages/django/db/backends/sqlite3/schema.py"", line 137, in _remake_table self.create_model(temp_model) File ""/Users/dwt/.virtualenvs/pycess/lib/python3.4/site-packages/django/db/backends/base/schema.py"", line 232, in create_model definition, extra_params = self.column_sql(model, field) File ""/Users/dwt/.virtualenvs/pycess/lib/python3.4/site-packages/django/db/backends/base/schema.py"", line 131, in column_sql db_params = field.db_parameters(connection=self.connection) File ""/Users/dwt/.virtualenvs/pycess/lib/python3.4/site-packages/django/db/models/fields/related.py"", line 1989, in db_parameters return {""type"": self.db_type(connection), ""check"": []} File ""/Users/dwt/.virtualenvs/pycess/lib/python3.4/site-packages/django/db/models/fields/related.py"", line 1980, in db_type rel_field = self.related_field File ""/Users/dwt/.virtualenvs/pycess/lib/python3.4/site-packages/django/db/models/fields/related.py"", line 1886, in related_field return self.foreign_related_fields[0] File ""/Users/dwt/.virtualenvs/pycess/lib/python3.4/site-packages/django/db/models/fields/related.py"", line 1620, in foreign_related_fields return tuple(rhs_field for lhs_field, rhs_field in self.related_fields) File ""/Users/dwt/.virtualenvs/pycess/lib/python3.4/site-packages/django/db/models/fields/related.py"", line 1607, in related_fields self._related_fields = self.resolve_related_fields() File ""/Users/dwt/.virtualenvs/pycess/lib/python3.4/site-packages/django/db/models/fields/related.py"", line 1592, in resolve_related_fields raise ValueError('Related model %r cannot be resolved' % self.rel.to) ValueError: Related model 'process.ProcessDef' cannot be resolved }}} That is, it seems as if the internal migration logic is missing the fact that it has just renamed a model, and is trying to look up a relation by it's old un-renamed name - and then failing. I have tried to reduce this to one squashed migration, but I'm not sure I entirely succeeded, as the bug seems to be transient with this migration, i.e. I get it in about 80-90% of cases, and removing more from it which *should* be unrelated seems to bring this ratio down quite drastically. So to sum it up, it feels like a race condition. Anyway, here it is: {{{ #!python # -*- coding: utf-8 -*- from __future__ import unicode_literals from django.db import models, migrations from django.conf import settings class Migration(migrations.Migration): dependencies = [ migrations.swappable_dependency(settings.AUTH_USER_MODEL), ] operations = [ migrations.CreateModel( name='FieldDef', fields=[ ('id', models.AutoField(primary_key=True, verbose_name='ID', serialize=False, auto_created=True)), ('name', models.CharField(max_length=200)), ('descript', models.CharField(max_length=200)), ('fieldhelp', models.CharField(max_length=200)), ('fieldtype', models.PositiveSmallIntegerField()), ('length', models.PositiveSmallIntegerField()), ('editable', models.NullBooleanField()), ('must', models.NullBooleanField()), ('type', models.PositiveSmallIntegerField()), ('parent', models.ForeignKey(to='process.FieldDef')), ], ), migrations.CreateModel( name='ProcessDef', fields=[ ('id', models.AutoField(primary_key=True, verbose_name='ID', serialize=False, auto_created=True)), ('name', models.CharField(max_length=200)), ('descript', models.CharField(max_length=200)), ('status', models.PositiveSmallIntegerField()), ('version', models.PositiveSmallIntegerField()), ('refering', models.ForeignKey(to='process.ProcessDef')), ], ), migrations.CreateModel( name='ProcInstance', fields=[ ('id', models.AutoField(primary_key=True, verbose_name='ID', serialize=False, auto_created=True)), ('starttime', models.DateTimeField()), ('stoptime', models.DateTimeField()), ('status', models.PositiveSmallIntegerField()), ('process', models.ForeignKey(to='process.ProcessDef')), ], ), migrations.AlterField( model_name='processdef', name='refering', field=models.ForeignKey(to='process.ProcessDef', null=True), ), migrations.AlterField( model_name='processdef', name='refering', field=models.ForeignKey(to='process.ProcessDef', blank=True, null=True), ), migrations.RenameModel( old_name='ProcessDef', new_name='ProcessDefinition', ), migrations.RenameModel( old_name='ProcInstance', new_name='ProcessInstance', ), migrations.RenameField( model_name='processinstance', old_name='status', new_name='runstatus', ), ] }}} You can see the project where this is from at https://github.com/pycess/pycess for reference. There are some old bugs in the bug database that look kind of similar (e.g. #22319) but not quite, which is why I am filing this new ticket." Bug closed Migrations 1.8 Normal needsinfo Unreviewed 0 0 0 0 0 0