Run migrations without loading views/urls

Question

I have following code in one of my views:

@ratelimit(method='POST', rate=get_comment_rate())
def post_comment_ajax(request):
    ...

However, upon initial ./manage.py migrate, get_comment_rate() requires a table in database, so I'm unable to run the migrations to create the tables. I ended up with following error:

Django.db.utils.ProgrammingError: relation .. does not exist

Is it possible to run migrations without loading views or is there a better way?

Answer 1

Running migrations triggers the system checks to run, which causes the views to load. There isn't an option to disable this.

It looks like the ratelimit library allows you to pass a callable.

@ratelimit(method='POST', rate=get_comment_rate)
def post_comment_ajax(request):

This would call get_comment_rate when the view runs, rather than when the module loads. This could be an advantage (value won't be stale) or a disadvantage (running the SQL query every time the view runs could affect performance.

In general, you want to avoid database queries when modules load. As well as causing issues with migrations, it can cause issues when running tests -- queries can go to the live db before the test database has been created.

If you are ok with this risk, one option would be to catch the exception in the decorator:

def get_comment_rate():
    try:
        ...
    except ProgrammingError:
        return '1/m'  # or some other default