DEFAULT_AUTO_FIELD should allow for diable migration for existing models

[qiu-lijie]

DEFAULT_AUTO_FIELD new in 3.2 will change existing models' pk to BigAutoField, as BigAutoField is the default for new projects. I believe there should be an option to disable this behaviour, i.e., not migrate existing models to BigAutoField. While I understand Django wants to move away AutoField and towards BigAutoField for pk, the current behaviour will make migrations for third-party apps, which is not desirable. Ideally, all third-party apps would also migrate their own models to use BigAutoField, but we all know that some don't get maintained as much, see examples below.

Migrations for 'account':
  /usr/local/lib/python3.8/site-packages/allauth/account/migrations/0003_auto_20210610_0705.py
    - Alter field id on emailaddress
    - Alter field id on emailconfirmation
Migrations for 'cities_light':
  /usr/local/lib/python3.8/site-packages/cities_light/migrations/0011_auto_20210610_0705.py
    - Alter field id on city
    - Alter field id on country
    - Alter field id on region
    - Alter field id on subregion

[Mariusz Felisiak]

While I understand Django wants to move away AutoField and towards BigAutoField for pk

First of all I would like to ensure you that this will not happen in the nearest future (maybe never). I can not imagine that we would change that before dropping support for all versions prior to 3.2.

the current behaviour will make migrations for third-party apps, which is not desirable

3rd-party apps can set AppConfig.default_auto_field to the 'django.db.models.AutoField' to avoid migrations, you can also set DEFAULT_AUTO_FIELD = 'django.db.models.AutoField' in your project.

We allowed customization at all levels (project, app, model) see ​release notes. Also it looks that ​django-allauth and ​django-cities-light don't officially support Django > 3.2, you can try to report this in their bugtrackers.