Migrate Database of Django 1.4 application to Django 1.8 version - django

Question

We have migrated the Django 1.4 application to Django 1.8 successfully. The Django 1.4 version of applicaiton is still in use in production until we go live with Django 1.8. The problem is that lots of data have been updated on production server which needs to be migrated to version 1.8. Is there any way I can migrate the data from database of 1.4 to 1.8 except manually doing that? Note that the model/database columns are different in both the version.
Can anybody suggest some good options ?
Thanks.

Answer 1

Required pre-reading
Django migrations:
https://docs.djangoproject.com/en/1.8/ref/django-admin/#makemigrations-app-label
Assuming you were using South:
https://docs.djangoproject.com/en/1.8/topics/migrations/#upgrading-from-south
Getting Started
Firstly dump your local database I prefer using mysql/postgres/whatever docs for this rather than using ./manage.py dumpdata.
You will also want to dump your production database as well just for safekeeping.
Next in your local environment I would dump the database and create a new database.
Then I would test that all your migrations actually work on a blank database.
These are the instructions for django 1.8
./manage.py makemirgrations
./manage.py migrate
That will help show up if any migrations are in an inconsistent state operating from a blank slate. If you encounter any errors they should be fixed first.
Given that works, now I would test that your migrations actually work against your production data.
So drop your local database, create a fresh one then load the production dump in.
If the tables are already configured correctly (i.e. they are in an up to date state in your production database) then you will need to fake all migrations.
./manage.py migrate --fake <appname>
However given that you have changed some models since upgrading to 1.8 in your local environment, then you might need to fake only some of the migrations. This could be the tricky part depending on the timing of when you upgraded and when you created the migrations.
Because django 1.7 will just create an initial migration for each app, you may need to actually break up the migration for some apps. That is, instead of 0001_initial you might need to manually break up that migration into 2 components:
1. a migration to match the current state of your production database
2. a migration to match any additional changes you have made to your model since then.
One way to do this is to checkout your first commit once you had django 1.8 working correctly locally then run
./manage.py makemigrations
then commit that
then go forward to your latest commit then run
./manage.py makemigrations
Now you should have 2+ migrations in each app that you have modified since upgrading to django 1.8.
Then you can fake initial on those apps that have 2+ new migrations for django 1.8
./manage.py migrate --fake-initial app1 app2
and the rest just
./manage.py migrate app3 app4
Now run your tests to confirm everything is working locally.
If you have changed migrations you will again want to test locally against a blank database to test that they work smoothly
Once that is working, record the 'migrate' commands that you used - then deploy your app to production and run just those migration commands once you have upgraded to django 1.8 on your server.
After Successful Completion
Take new dumps of your local and production databases
Uninstall South (assuming you had it installed before) from local and production environments
I'm sure there are a couple of holes in the above but hopefully that gives you the gist of what you need to do.