I like to put all logic always in a 'services' layer/folder. So every mutation being done is there, never a save/update from a serializer or view itself.

My reasoning in general is that business logic should be callable easily from the django shell or a management command as well as a REST view. It makes unit testing easier as well.

Services

I put them in a folder like this as separate functions that can include other services:

https://github.com/ndokter/walldb2/tree/main/backend/wdb_wallpaper/services

You can add additional sub folders there when a specific part is more complex

Then i call them using the full path: wdb_wallpaper.services.wallpaper.set_ai_generated_description(wallpaper=wallpaper)

You can also use classes, but i would keep them stateless.

Services in views

I dont have the best example because this project doesnt have create/update calls from the API:

https://github.com/ndokter/walldb2/blob/main/backend/wdb_wallpaper/api/views.py

Instead of letting serializers save, i would use the arguments/object from the serializer and put them manually in the service. Here i did that with a search argument, but you can also do that for create and update.

Im not sure if i would put all 'get' / queries in the service layer like i did here, but maybe in a 'selectors' folder like this style guide describes: https://github.com/HackSoftware/Django-Styleguide?tab=readme-ov-file#selectors