This is pretty similar to what django-ninja offers as well with their Schema modeling [1]. I found it to be a big help personally and always wanted something for fastapi.

Django-ninja is essentially the fastapi of the django world so this library would be enough for me to go all in on fastapi. I just never felt like I found a python orm with the level of ergonomics of django + async of modern python

[1] https://django-ninja.dev/guides/response/django-pydantic/