How to create a new database for an existing App using Django South and set default values

djangodjango-databasedjango-south

I'm working with an OS project that uses South to migrate the database.
I'm building a new database from scratch and I want to make sure South is setup so I can easily update the database in the future.

It seems this process should be:

create the db
syncdb
migrate

However, when I try to migrate the databases, one of the the earlier migrations(migration 0004 and they go to 0009) throws an exception:

ValueError: You cannot add a null=False column without a default value.

I don't understand how to add a default value to migration 0004 so this exception isn't thrown.

The migrations don't need to be run through because the database is empty.

However, south_migrationhistory must contain a list of all migrations and when they were applied.

I tried to hack it and just add migration 0009 to the database manually, but this threw another error because the intermediary migrations had not been run.
I also tried to add a field to database to see if I could figure out the syntax of add_column would look like with a default value of 0 supplied.
The format looks totally different than these older migrations.

Here are the 2 different versions of the add_column syntax:

#0004 syntax:  
db.add_column('experiments_dailyreport', 'test_group_size', orm['experiments.dailyreport:test_group_size'])
#0009 syntax:
syntax db.add_column('experiments_dailyreport', 'test_group_size', self.gf('django.db.models.fields.IntegerField')(default=0), keep_default=False)

So, I'm guessing there was a change in the South code between when 0004 was created and today.

Is there a way to build the database with syncdb and then somehow update south_migrationhistory without running manage.py migrate ?

If you have an existing app with South migrations, how would you build a new database from scratch?

I can't migrate because there is no default set on a integer field.
How do I set a default in an older migration? The field doesn't even exist anymore.

syntaxes attempted:

db.add_column('experiments_dailyreport', 'test_group_size', orm['experiments.dailyreport:test_group_size'], {'default': 0})
#throws ValueError: You cannot add a null=False column without a default value.
db.add_column('experiments_dailyreport', 'test_group_size', self.gf('django.db.models.fields.IntegerField')(default=0), keep_default=False)
#throws AttributeError: Migration instance has no attribute 'gf'

I'm using South-0.7.2-py2.7.egg

Best Answer

Andrew Godwin provided an answer:

Yes, use:

./manage.py syncdb --all

then:

./manage.py migrate --fake

This will, however, also ignore any migrations that add in data to the database.

Related Solutions

R – django and south migration with conflicts (0007_two … and 0007_one) how to solve

After doing the migrate --merge or rollback-and-migrate, if you know that the most recent migration now has inaccurate frozen models, I would just create a new no-op migration for the purposes of bringing the frozen models up to date. Just run ./manage.py startmigration myapp --empty freeze_noop. Now your frozen models will be up-to-date for the next time you want to autodetect a real migration.

Maybe it seems a little ugly to create a no-op migration, but to me this seems cleaner than either of the manual history-editing options you suggested. You can think of the no-op migration as the equivalent of a "merge commit" in a DVCS.

This issue ought to be mentioned in this section of the South docs; I've filed an issue for it. (Update: now it is.)

Renaming an app with Django and South

I agree with Laksham that you should avoid this situation. But sometimes, we have to. I've faced this situation in the past and I've managed it this way.

If you want to avoid losing data you can dump the old application data into a json file.

python manage.py dumpdata old_app --natural --indent=4 1> old_app.json

Note the --natural option that will force the content types to be exported with their natural keys (app_name, model)

Then you can create a small command to open this json file and to replace all the old_app references with the new_app.

Something like this should work

class Command(BaseCommand):
    help = u"Rename app in json dump"

    def handle(self, *args, **options):
        try:
            old_app = args[0]
            new_app = args[1]
            filename = args[2]
        except IndexError:
            print u'usage :', __name__.split('.')[-1], 'old_app new_app dumpfile.json'
            return

        try:
            dump_file = open(filename, 'r')
        except IOError:
            print filename, u"doesn't exist"
            return

        objects = json.loads(dump_file.read())
        dump_file.close()

        for obj in objects:
            obj["model"] = obj["model"].replace(old_app, new_app, 1)

            if obj["fields"].has_key("content_type") and (old_app == obj["fields"]["content_type"][0]):
                obj["fields"]["content_type"][0] = new_app

        dump_file = open(filename, 'w')
        dump_file.write(json.dumps(objects, indent=4))
        dump_file.close()

Then rename the application, change the name in INSTALLED_APPS.

Then, you should remove all south migrations, regenerate and apply an initial migration for the new app. Then run the SQL command:

update django_content_type set app_label='new_app' where app_label='old_app'

Then launch a south migrate for the new app in order to create the tables and load the json file.

python manage.py loaddata old_app.json

I've done something similar on a project and it seems to work ok.

I hope it helps

Best Answer

Related Solutions

R – django and south migration with conflicts (0007_two … and 0007_one) how to solve

Renaming an app with Django and South

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