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
21236	Migrations: error applying unique_together	Harry Percival		"This occurs when trying to apply a migration that contains a single modification: the application of a unique_together constraint.  full traceback at the end, but the problem seems to come around here:

{{{
    self.create_model(temp_model)
  File ""/workspace/virtualenv/lib/python3.3/site-packages/django/db/backends/schema.py"", line 225, in create_model
    columns = [model._meta.get_field_by_name(field)[0].column for field in fields]
  File ""/workspace/virtualenv/lib/python3.3/site-packages/django/db/models/options.py"", line 387, in get_field_by_name
    % (self.object_name, name))
django.db.models.fields.FieldDoesNotExist: Item has no field named 'l'
}}}

Context: this is a model whose unique_together constraint is on its only two fields, which in this case are called `list` and `item`:
{{{#!python
        migrations.AlterUniqueTogether(
            unique_together = set(['text', 'list']),
            name = 'item',
        ),
}}}

I did a little digging. Inside the 'schema.py', in the `create_model` function, a little debug print like this:

{{{#!python
 print('unique_together', model._meta.unique_together)
}}}

gives

{{{#!python
unique_together [('l', 'i', 's', 't'), ('t', 'e', 'x', 't')]
}}}

Looks like some list comprehension somewhere has gone wrong?


Minimal repro:
Just checkout this repo

https://github.com/hjwp/django-migrations-unique_together-bug-minimal-repro

make sure you're running the latest dev django. there's a requirements.txt in there. 

then just cd into myproject, run python manage.py syncdb, and you should get:

{{{
$ python manage.py syncdb
Operations to perform:
  Synchronize unmigrated apps: sessions, admin, messages, auth, staticfiles, contenttypes
  Apply all migrations: myapp
Synchronizing apps without migrations:
  Installing custom SQL...
  Installing indexes...
Installed 0 object(s) from 0 fixture(s)
Running migrations:
  Applying myapp.0002_auto...Traceback (most recent call last):
  File ""manage.py"", line 10, in <module>
    execute_from_command_line(sys.argv)
  File ""/tmp/django-migrations-unique_together-bug-minimal-repro/venv/local/lib/python2.7/site-packages/django/core/management/__init__.py"", line 397, in execute_from_command_line
    utility.execute()
  File ""/tmp/django-migrations-unique_together-bug-minimal-repro/venv/local/lib/python2.7/site-packages/django/core/management/__init__.py"", line 390, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File ""/tmp/django-migrations-unique_together-bug-minimal-repro/venv/local/lib/python2.7/site-packages/django/core/management/base.py"", line 242, in run_from_argv
    self.execute(*args, **options.__dict__)
  File ""/tmp/django-migrations-unique_together-bug-minimal-repro/venv/local/lib/python2.7/site-packages/django/core/management/base.py"", line 289, in execute
    output = self.handle(*args, **options)
  File ""/tmp/django-migrations-unique_together-bug-minimal-repro/venv/local/lib/python2.7/site-packages/django/core/management/base.py"", line 419, in handle
    return self.handle_noargs(**options)
  File ""/tmp/django-migrations-unique_together-bug-minimal-repro/venv/local/lib/python2.7/site-packages/django/core/management/commands/syncdb.py"", line 22, in handle_noargs
    call_command(""migrate"", **options)
  File ""/tmp/django-migrations-unique_together-bug-minimal-repro/venv/local/lib/python2.7/site-packages/django/core/management/__init__.py"", line 159, in call_command
    return klass.execute(*args, **defaults)
  File ""/tmp/django-migrations-unique_together-bug-minimal-repro/venv/local/lib/python2.7/site-packages/django/core/management/base.py"", line 289, in execute
    output = self.handle(*args, **options)
  File ""/tmp/django-migrations-unique_together-bug-minimal-repro/venv/local/lib/python2.7/site-packages/django/core/management/commands/migrate.py"", line 124, in handle
    executor.migrate(targets, plan, fake=options.get(""fake"", False))
  File ""/tmp/django-migrations-unique_together-bug-minimal-repro/venv/local/lib/python2.7/site-packages/django/db/migrations/executor.py"", line 60, in migrate
    self.apply_migration(migration, fake=fake)
  File ""/tmp/django-migrations-unique_together-bug-minimal-repro/venv/local/lib/python2.7/site-packages/django/db/migrations/executor.py"", line 89, in apply_migration
    migration.apply(project_state, schema_editor)
  File ""/tmp/django-migrations-unique_together-bug-minimal-repro/venv/local/lib/python2.7/site-packages/django/db/migrations/migration.py"", line 92, in apply
    operation.database_forwards(self.app_label, schema_editor, project_state, new_state)
  File ""/tmp/django-migrations-unique_together-bug-minimal-repro/venv/local/lib/python2.7/site-packages/django/db/migrations/operations/models.py"", line 126, in database_forwards
    getattr(new_model._meta, ""unique_together"", set()),
  File ""/tmp/django-migrations-unique_together-bug-minimal-repro/venv/local/lib/python2.7/site-packages/django/db/backends/sqlite3/schema.py"", line 131, in alter_unique_together
    self._remake_table(model, override_uniques=new_unique_together)
  File ""/tmp/django-migrations-unique_together-bug-minimal-repro/venv/local/lib/python2.7/site-packages/django/db/backends/sqlite3/schema.py"", line 55, in _remake_table
    self.create_model(temp_model)
  File ""/tmp/django-migrations-unique_together-bug-minimal-repro/venv/local/lib/python2.7/site-packages/django/db/backends/schema.py"", line 223, in create_model
    columns = [model._meta.get_field_by_name(field)[0].column for field in fields]
  File ""/tmp/django-migrations-unique_together-bug-minimal-repro/venv/local/lib/python2.7/site-packages/django/db/models/options.py"", line 387, in get_field_by_name
    % (self.object_name, name))
django.db.models.fields.FieldDoesNotExist: Item has no field named 't'
}}}

Full trac
{{{
/home/harry/Dropbox/book/source/chapter_09/virtualenv/lib/python3.3/site-packages/django/db/backends/schema.py


  Applying myapp.0002_auto...Traceback (most recent call last):
  File ""/tmp/repro/venv/lib/python3.3/site-packages/django/db/models/options.py"", line 381, in get_field_by_name
    return self._name_map[name]
AttributeError: 'Options' object has no attribute '_name_map'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File ""/tmp/repro/venv/lib/python3.3/site-packages/django/db/models/options.py"", line 384, in get_field_by_name
    return cache[name]
KeyError: 't'

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 ""/tmp/repro/venv/lib/python3.3/site-packages/django/core/management/__init__.py"", line 397, in execute_from_command_line
    utility.execute()
  File ""/tmp/repro/venv/lib/python3.3/site-packages/django/core/management/__init__.py"", line 390, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File ""/tmp/repro/venv/lib/python3.3/site-packages/django/core/management/base.py"", line 242, in run_from_argv
    self.execute(*args, **options.__dict__)
  File ""/tmp/repro/venv/lib/python3.3/site-packages/django/core/management/base.py"", line 289, in execute
    output = self.handle(*args, **options)
  File ""/tmp/repro/venv/lib/python3.3/site-packages/django/core/management/commands/migrate.py"", line 124, in handle
    executor.migrate(targets, plan, fake=options.get(""fake"", False))
  File ""/tmp/repro/venv/lib/python3.3/site-packages/django/db/migrations/executor.py"", line 60, in migrate
    self.apply_migration(migration, fake=fake)
  File ""/tmp/repro/venv/lib/python3.3/site-packages/django/db/migrations/executor.py"", line 89, in apply_migration
    migration.apply(project_state, schema_editor)
  File ""/tmp/repro/venv/lib/python3.3/site-packages/django/db/migrations/migration.py"", line 92, in apply
    operation.database_forwards(self.app_label, schema_editor, project_state, new_state)
  File ""/tmp/repro/venv/lib/python3.3/site-packages/django/db/migrations/operations/models.py"", line 126, in database_forwards
    getattr(new_model._meta, ""unique_together"", set()),
  File ""/tmp/repro/venv/lib/python3.3/site-packages/django/db/backends/sqlite3/schema.py"", line 131, in alter_unique_together
    self._remake_table(model, override_uniques=new_unique_together)
  File ""/tmp/repro/venv/lib/python3.3/site-packages/django/db/backends/sqlite3/schema.py"", line 55, in _remake_table
    self.create_model(temp_model)
  File ""/tmp/repro/venv/lib/python3.3/site-packages/django/db/backends/schema.py"", line 223, in create_model
    columns = [model._meta.get_field_by_name(field)[0].column for field in fields]
  File ""/tmp/repro/venv/lib/python3.3/site-packages/django/db/backends/schema.py"", line 223, in <listcomp>
    columns = [model._meta.get_field_by_name(field)[0].column for field in fields]
  File ""/tmp/repro/venv/lib/python3.3/site-packages/django/db/models/options.py"", line 387, in get_field_by_name
    % (self.object_name, name))
django.db.models.fields.FieldDoesNotExist: Item has no field named 't'
}}}
"	Bug	new	Migrations	dev	Normal				Unreviewed	0	0	0	0	0	0