Squashing Old References with Django Migrations

The other day I found a small typo in a function I was referencing in the upload_to field option in one of my models. I fixed the nasty typo, only to discover I had broken the migrations, as it was also being referenced in one of them.

According to the docs, we can make use of squashing to remove these old references. Here’s how I managed to solve my OCD inspired issue.

Making the Changes

Freely apply all the changes that are required, but keep the old references:

from django.db import models


# Old function
def my_supr_function(instance, filename):
    # Move the implementation to the new function
    pass


# Renamed function
def my_super_function(instance, filename):
    # Some advanced code here
    return 2 + 2


class MyModel(models.Model):
    # Update the 'upload_to' reference here
    image = models.ImageField(upload_to=my_super_function)

Making the Migrations

Tell Django you want to create a new migration based on these changes:

$ ./manage.py makemigrations --name rename-function

Squashing

We now have a brand new migration which no longer references my_supr_function (the function with the typo). We can know squash our migrations from the point where it was first referenced, up to this newly created migration.

$ ./manage.py squashmigrations my_app 0005 0009

Applying migrations

We can’t go around life having unimplemented functions whose names have typos, our end goal here is to get rid of them, but unfortunately there is one more step required before we can do that.

Go ahead and commit your changes, and apply the migrations on any production server you have, plus your development machine of course.

$ ./manage.py migrate

Cleaning Up

Once migrations are up to date, it is safe to remove not only the typo function, but all the squashed migrations as well. Peace at last.