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 through my business service layer to enforce proper business rules and validation. Validation – I don’t want to perform validation in the controller using the various validation attributes ( such as [Required]) on my domain model entities because this sheds light on my front end. Not to mention this service can also be implemented through a WPF front end.
Since my validation is being done in my service layer, what are best practices for returning values back to the UI? I don’t want a ‘void addWhatever(int somethingsID)’, because I need to know if it failed. Should it be a boolean? Should it be a Enum? Should I take advantage of exception handling? Or should I return some IValidationDictionary object similar to that used by MVC when adorning validation attributes to Model objects? (which I could use an adapter pattern in the UI later if needs be)
I would like to pass my entity from the controller to the service layer, and understand whether or not validation/data-persistence failed. I also don’t want to lose sight on the fact that I need to return a view indicating the proper error messages for each field that may have failed validation (I’d like to keep this as painless as possible).
I have had several ideas, all of which don’t feel right. I feel the answer includes View-specific-model entities, but this leads to a whole mapping issue that must be dealt with, not to mention this violates the DRY (Don’t repeat yourself) principle. What is best practice?
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.