Check if merge migration is required, without database

Question

To check if merge migrations are required, I can run manage.py makemigrations --check or manage.py makemigrations --dry-run

However, both of those require the database to be up. If it's not up, it will error out with something like

django.db.utils.OperationalError: (2002, "Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2)")

Theoretically, since a merge migration issue occurs because of two migration with the same parent, you don't need the database instance to be up to check for this condition.

I need this because I want my CI to check for this case. I can spin up a docker database but it's extra work for something that's not even logically dependent. I'm also sure there are people out there who are interested in checking for this in their CI, who don't want to deal with containerization.

Has anyone found an easy way to to check for migration merge conflicts without needing a database up?

Answer 1

Since the goal is to run makemigrations --dry without a mysql database up, the easiest workaround I came up with is to create a new settings file called makemigrations_settings.py that overrides the database to use the builtin sqlite database.

from your_main_settings import *
DATABASES = {
    'default' : {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': 'database_name',
        'USER': 'your_mom',
        'PASSWORD': '',
        'HOST': '',
        'PORT': '',
    },
}

Then you can run

python manage.py makemigrations --check --settings yourapp.makemigrations_settings

Alternatively, you can less elegantly do something like

if (sys.argv[0:2] == ['manage.py', 'makemigrations']
    and ('--dry-run' in sys.argv or '--check' in sys.argv)):
            DATABASES = {
                'default' : {
                    'ENGINE': 'django.db.backends.sqlite3',
                    'NAME': 'database_name',
                    'USER': 'your_mom',
                    'PASSWORD': '',
                    'HOST': '',
                    'PORT': '',
                }
            }