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.
