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  • "Validation should be done before you hit the BLL" Different kinds of validation exist, and this statement is not correct for all of them. When the validation relies on the application of business rules, then the validation definitely belongs in, not before the BLL. UI validation (which would happen before the BLL) is valuable for UX purposes but generally still requires a last line of defense in the BLL if these failures would break the system in any way. Commented Sep 23, 2024 at 1:57
  • On re-read of my comment, just to be clear: not every validation rule can easily be implemented as a UI validation rule, e.g. when it requires very active coupling to the persistence mechanism or requires some kind of external validation. Some validation makes more sense to put on the BLL alone without a UI validation counterpart. Commented Sep 23, 2024 at 2:21
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    yeah i think you might be getting into very fine differences in the meaning of "validation" here. what i mean is, just throw errors in the BBL, do the validation in its own class. If you can't, because you have some transactional validation or whatever then do the best you can Commented Sep 23, 2024 at 9:23