ASP.NET MVC View Model pattern - validation and database operation

At the start of the development I faced with problem called "an impedance mismatch between domain model and the view". To solve this problem I decide to use ViewModel pattern - for every view (that is strongly typed) we create viewmodel class. But where is the validation logic is locate - in viewmodel classes or in our domain model objects? And where we need t开发者_如何转开发o perform operations to query database - in controller action, and then populate viewmodel or straight in viewmodel?

Thank you.

You should have validation logic for the viewmodel. This is what the view sends and what should be validated. As far as populating the viewmodel is concerned here's how to proceed: write a repository which queries the database and returns models. Then map those models to viewmodels (AutoMapper can help you here). Finally return viewmodels to the view. This also works the other way around: the users POSTs some data to a controller action as the form of a viewmodel which once validated is mapped back to a model and passed to the repository for update.

As an alternative to Data Annotations you may take a look at FluentValidation for validating your view models. It integrates nicely with ASP.NET MVC.