Referencing a function in a model field definition, and then removing that reference (and function) after running a migration raises an exception

[Jesse]

With a FileField you can define a function for the upload_to argument. If you reference a function within that field, and then decide to modify the field later by removing the function reference (and also the function), the migrations will cause the server to fail to start because it can't find the function that was previously referenced.

For example:

def destination():
  return "path"

...

file = models.FileField(upload_to=destination)

Then later on I decide I don't need the function

file = models.FileField(upload_to="hardcoded path")

Now whenever I try to run the server locally or do a migration, I get: "AttributeError: 'module' object has no attribute 'destination'". The only meaningful workaround is to delete all migrations

[Simon Charette]

This a ​documented caveat of historical models.

You can either can squash these migrations or copy your upload_to function definition into the migration files referencing it.