[globular-toast]

Thanks for your reply. I'm currently in a stage of falling out of love with Django and trying to get my thoughts together on why that is.

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.

[irjustin]

Yeah definitely understand the frustration. I've been there and while I don't think we've found _the_ solution, we've settled into a flow that we're generally happy with.

For us we separate validations in two. Business and Data validations, which are generally defined as:

- Business: The Invoice in Country X is needs to ensure Y and Z taxes are applied at Billing T+3 days otherwise throw an error.

- Data Validation: The company's currency must match the country it operates in.

Business validations and logic always go inside services where as data validations are on the model. Data validations apply to 100% of all inserts. Once there's an IF statement segmenting a group it becomes business validation.

I could see an argument as to why the above is bad because sometimes it's a qualitative decision. Once in a while the lines get blurry, a data validation becomes _slightly_ too complex and an arguement ensues as to whether it's data vs business logic.

Our team really adheres to services and not fat models, sorry DHH.

To me, it's all so controversial whatever you pick will work out just fine - just stick to it and don't get lazy about it.

[globular-toast]

Services are definitely better and a solid part of a domain-driven design. The trouble is with Django I think it's a bandaid on a fundamentally broken architecture. The models end up anaemic because they're trying to be two things at once. It's super common to see things like services directly mutating model attributes and set up relationships manually by creating foreign keys etc. All of that should be hidden far away from services.

The ultimate I think is Domain-Driven Design (or Clean Architecture). This gives you a true core domain model that isn't constrained by frameworks etc. It's as powerful as it can be in whatever language you use (which in the case of Python is very powerful indeed). Some people have tried to get it to work with Django but it fights against you. It's probably more up front work as you won't get things like Django admin, but unless you really, truly are doing CRUD, then admin shouldn't be considered a good thing (it's like doing updates directly on the database, undermining any semblance of business rules).