I think Django seems confused on the issue of clean/validation. On the one hand, it could say the "model" is just a database table and any validation should live in the business logic of your application. This would be a standard way of architecting a system where the persistence layer is in some peripheral part that isn't tied to the business logic. It's also how things like SQLAlchemy ORM are meant to be used. On the other hand, it could try to magically handle the translation of real business objects (with validation) to database tables.

It tries to do both, with bad results IMO. It sucks to use it on the periphery like SQLAlchemy, it's just not designed for that at all. So everyone builds "fat" models that try to be simultaneously business objects plus database tables. This just doesn't work for many reasons. It very quickly falls apart due to the object relational mismatch. I don't know how Rails works, but I can't imagine this ever working right. The only way is to do validation in the business layer of the application. Doing it in the views, like rest framework or form cleans is even worse.