MVC Validation - Keep it DRY with a service layer - What is best practice?

Question

I am trying to adhere to best multi-layer design practices, and don\'t want my MVC controller to interact with my DAL (or any IRepository for that matter). It must go throug

Answer 1

I know, it seems like doing MVC validation violates DRY, but in reality.. it doesn't.. at least not for most (non-trivial) applications.

Why? Because your view's validation requirements are quite often different from your business objects validation requirements. Your views validation concerns itself with validating that a specific view is valid, not that your business model is valid.

Sometimes those two are the same, but if you build your app so that the view requires the business model to be valid, then you are locking yourself into this scenario. What happens if you need to split object creation into two pages? What happens if you decide to use the service layer for a web service? By locking your UI into a business layer validation scenario you severly cripple the kinds of solutions you can provide.

The view is validation of the input, not validation of the model.