Where do you put your validation in asp.net mvc 3?

Question

One common recommended practice in asp.net mvc is that you should not send your business models to your views.. instead you should create viewmodels specific to each view.

Answer 1

Great answer by RPM1984, and nice code sample.

My view is still that using Variant 2 from the start is a pragmatic balance between productivity and structure, but you always have to be willing to move to Variant 3 in some cases, so I advocate a mix of the two approaches where logical. Patterns & Practices however recommend always doing Variant 3 as it is the ideal separation of concerns etc, and it avoids you using two approaches in the same solution which some people don't like and many customers I work with pick Variant 3 and run with that for all models.

I think the key is what RPM1984 said - reusing your business entities inside your View Models is useful for the sake of reusing the validation, but do bear in mind that often your business logic needs to do different validation too (e.g. checking the record doesn't already exist). If you use Variant 3 it empowers you to focus your View Model validation purely on the needs of your views (at the expense of a little extra effort) but you will always need some kind of business logic validation too.