Django Commands: makemigrations or migrate?

I remember when I first started with Django and had to deal with migrations. It wasn't clear to me when I needed to run makemigrations or migrate, and would generally always run the commands if things weren't working as expected.

Here is a simple how-to manual that should help you make sense of these commands.

When to run makemigrations

You'll want to run python manage.py makemigrations whenever you make a change to a model, even if it is updating the description on a field.

Adding or updating functions inside of a model does not need a migration, but you can still run makemigrations just in case.

If you get 'No changes detected' from the output, you're good to go. Otherwise, you'll see output like this:

Migrations for 'mymodel':
  project/app/migrations/0010_auto_20180420_1726.py:
    - Alter field title on model1
    - Alter field location on model2

Then you will need to do two more steps:

run python manage.py migrate to apply the change to your data
add the new migration file to the repository when you check in the changes.

Extra tip:

Applying a name to the migration will make it easier to see what each migration was for.

For example:

$ python manage.py makemigrations --name increase_max_lengths

...will create a migration file:

project/app/migrations/0010_increase_max_lengths.py.

The number is automatically added to the front - this is sequential, and the number will depend on how many migrations you already have.

When to run migrate

You will need to migrate whenever new migrations are available that have not yet been applied to the data in the current instance.

These cases would be:

After you've created new migrations with makemigrations
When you update to the latest code, and someone else has added new migrations
When Django tells you, "You have x unapplied migration(s). Your project may not work properly until you apply the migrations..." This is a message you would see when starting the site.

In any of these cases, run:

$ python manage.py migrate

Django's output is helpful on this one. It will tell you if there are no migrations to apply, or even if you need to run makemigrations when you have changes that aren't in a migration yet.

Undo a migration

If you ran a migration that you need to update or change, you may need to go backwards through the migrations.

Let's say you want to 'undo' the migration for 0010_increase_max_lengths.py that was done earlier.

Specify the app the migration lives in, and the number of the previous migration (full name not necessary):

$ python manage.py migrate app 0009

Replace 'app' with the name of your app. You'll see output that looks like this:

Operations to perform:
  Target specific migration: 0009_content_homepage, from app
Running migrations:
  Rendering model states... DONE
  Unapplying app.0010_increase_max_lengths... OK

Sometimes you may get a message that the migration cannot be unapplied. This is one reason why it's always good to test before running migrations on the production data!

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