On a Django app with some self-made (but close to available plugin methods) multi-tenant implementation, I would like to run a migration (a simple add_column this time) with South that could apply on all schemas. I have a configuration very close to this one.
I would like to skip any pure SQL queries if possible. I can get a list of the schemas name from the ORM properly, but then I wonder if I have the possibility to access the tables from the various schemas in a somehow propre way.
I have a hook to be able to change the DB_HOST and DB_SCHEMA via parameters at some level, but I think not to be able to loop cleanly this way inside the forwards migration method of South.
This question is quite high-level, but I mainly wonder if somebody had to face the same kind of question and I am curious to know if there is some clever way to handle it !
Regards, Matt
Fine, not so many people seem to have experience or to be concerned with this quite specific problem. I have tried some things here and there and I also got some support from the South mailing-list that helped me to understand some points.
Basically, the solution I implemented is the following:
I have a quite normal migration file autogenerated via South's schemamigration. But I have changed the table name of the add_column and delete_column to schema.table_name. The schema is provided by importing the multi-tenant middleware.
The migration is then applied only if the schema is not run against the public schema. It is actually not meant to be run standalone, or only with database and schema kwargs, but rather from a migration runner that is a new django command.
The runner has unfortunately to call the migration externally, in order to go through the middleware each time again. One other trick is that we have to get the previous state of migration, in order to fake it back to the previous state for south after each tenant migration.
Here is my snippet :
from subprocess import call
import os
from django.core.management.base import BaseCommand
from south.models import MigrationHistory
from myapp.models import MyModel
class Command(BaseCommand):
def handle(self, *args, **options):
#the only allowed arg is the prefix version and it should have a length of 4 (i.e. 0002)
applied = MigrationHistory.objects.filter(app_name='myapp').latest('applied')
current_version = applied.migration[:4]
call_args = ['python', os.path.join('bin', 'manage.py'), 'migrate', 'myorderbird.app.backups']
if len(args) == 1 and len(args[0]) == 4:
call_args.append(args[0])
obje_call_args = None
for obje in MyModel.objects.all():
if obje.schema_exists:
# fake the migration of the previous venue back to the current version
if obje_call_args:
obje_call_args = obje_call_args[:4] + [current_version, '--fake'] + obje_call_args[len(obje_call_args)-3:]
call(obje_call_args)
# migrate the venue in the loop
obje_call_args = list(call_args)
obje_call_args.extend(['--database={}'.format(obje.db), '--schema={}'.format(obje.schema)])
call(venue_call_args)