Recover from failed migration - django

Question

When running
python3 manage.py migrate
I was asked what the default value of 'id' should be and entered 1. I had read
https://docs.djangoproject.com/en/1.9/howto/writing-migrations/#migrations-that-add-unique-fields
but that was a bit too complicated for me so tried 1.
Now when I run
python3 manage.py migrate
I get the following error:
vagrant#vagrant-ubuntu-trusty-64:/vagrant/grader$ python3 manage.py migrate
Operations to perform:
Apply all migrations: admin, core, contenttypes, auth, sessions
Running migrations:
Rendering model states... DONE
Applying core.0002_auto_20160103_1302...Traceback (most recent call last):
File "/usr/local/lib/python3.4/dist-packages/django/db/backends/utils.py", line 64, in execute
return self.cursor.execute(sql, params)
psycopg2.ProgrammingError: multiple default values specified for column "id" of table "core_student"
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "manage.py", line 10, in <module>
execute_from_command_line(sys.argv)
File "/usr/local/lib/python3.4/dist-packages/django/core/management/__init__.py", line 350, in execute_from_command_line
utility.execute()
File "/usr/local/lib/python3.4/dist-packages/django/core/management/__init__.py", line 342, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/usr/local/lib/python3.4/dist-packages/django/core/management/base.py", line 348, in run_from_argv
self.execute(*args, **cmd_options)
File "/usr/local/lib/python3.4/dist-packages/django/core/management/base.py", line 399, in execute
output = self.handle(*args, **options)
File "/usr/local/lib/python3.4/dist-packages/django/core/management/commands/migrate.py", line 200, in handle
executor.migrate(targets, plan, fake=fake, fake_initial=fake_initial)
File "/usr/local/lib/python3.4/dist-packages/django/db/migrations/executor.py", line 92, in migrate
self._migrate_all_forwards(plan, full_plan, fake=fake, fake_initial=fake_initial)
File "/usr/local/lib/python3.4/dist-packages/django/db/migrations/executor.py", line 121, in _migrate_all_forwards
state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
File "/usr/local/lib/python3.4/dist-packages/django/db/migrations/executor.py", line 198, in apply_migration
state = migration.apply(state, schema_editor)
File "/usr/local/lib/python3.4/dist-packages/django/db/migrations/migration.py", line 123, in apply
operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
File "/usr/local/lib/python3.4/dist-packages/django/db/migrations/operations/fields.py", line 62, in database_forwards
field,
File "/usr/local/lib/python3.4/dist-packages/django/db/backends/base/schema.py", line 396, in add_field
self.execute(sql, params)
File "/usr/local/lib/python3.4/dist-packages/django/db/backends/base/schema.py", line 110, in execute
cursor.execute(sql, params)
File "/usr/local/lib/python3.4/dist-packages/django/db/backends/utils.py", line 79, in execute
return super(CursorDebugWrapper, self).execute(sql, params)
File "/usr/local/lib/python3.4/dist-packages/django/db/backends/utils.py", line 64, in execute
return self.cursor.execute(sql, params)
File "/usr/local/lib/python3.4/dist-packages/django/db/utils.py", line 95, in __exit__
six.reraise(dj_exc_type, dj_exc_value, traceback)
File "/usr/local/lib/python3.4/dist-packages/django/utils/six.py", line 685, in reraise
raise value.with_traceback(tb)
File "/usr/local/lib/python3.4/dist-packages/django/db/backends/utils.py", line 64, in execute
return self.cursor.execute(sql, params)
django.db.utils.ProgrammingError: multiple default values specified for column "id" of table "core_student"
How can I recover from this failed migration? I went into the psql command promt and typed
SELECT * FROM core_students
It returned 0 rows so I don'w know why I have a problem.
Shouldn't Django automatically make the 'id' field be unique numbers?
EDIT:
The id has been auto generated by the Django migration.
student model:
class Student(models.Model):
created = models.DateTimeField(auto_now_add=True)
updated = models.DateTimeField(auto_now=True)
owner = models.ForeignKey('auth.User', related_name='students')
identity_number = models.CharField(max_length=50)
first_name = models.CharField(max_length=50)
last_name = models.CharField(max_length=50)

Answer 1

I often run into a similar problem where a migration fails for whatever reason, and only part of it gets applied to the database.
In theory you should be able to go into the database and run queries to finish the migration, but knowing what exact queries to run and what parts of the migration haven't been run is difficult in my experience.
The most dependable way I've found to fix it is to fake the migration, then back up the model, comment it out in models.py, then make a migration to delete it, then fake that as well. Then I can go into the database, drop the table, and then make a new migration to recreate it the way I now want to be.
Here are the commands I run:
python manage.py migrate --fake [appname] #fake the failed migration
#comment out the model in models.py and back up the data
python manage.py makemigrations [appname]
python manage.py migrate --fake [appname] #fake the migration to delete
the table
python manage.py dbshell
#drop the table. Mysql would be: DROP TABLE [appname]_[modelname];
#exit dbshell
#Uncomment the model in models.py adding in whatever changes were originally wanted
python manage.py makemigrations [appname]
python manage.py migrate #assuming your model change is valid, this should work this time.
#reload your data into the table
No, it's not elegant, but it gets django migrations working again without having to guess how far django got through a migration before it failed.