How ASP .NET MVC architecture fits into the traditional multi layered architecture

Question

Moving from the traditional way of architecting web applications with a Business Layer, Service Layer, Data Access Layer and a Presentation Layer to the MVC design pattern, I find it difficult to understand how it fits in the old model.

It seems to be that the MVC model itself already has done allot of the separation of concerns that is needed and used to be achieved via a layered architecture. Can someone shed some light on this subject please?

As a reference, below is how I understand it, please share your view on this

MVC Views and Controllers along with View Models -are- Presentation Layer

MVC Models - could be - Data Access Layer or Business Layer or even Service Layer

Answer 1

I see the Asp.Net MVC part only as the view (or presentation) part of the whole application.

I struggled too with the problem how to structure the app in a proper way.
Following the Onion Architecture I heard about here (and especially the image found here), my solution looks this way:

• Project.Core
  Business logic/services implementations, entities, interfaces that must be implemented by the other projects (i.e. "IRepository", "IAuthenticationService",...)
• Project.Data
  DB connection - in my case NHibernate repositories and entity-mappings go here. Implements data-interfaces of Project.Core
• Project.UI.Web
  The Asp.Net MVC ("presentation") project - it wires the whole app together.
  Has implementations for Interfaces in Project.Core and wires them (and those from Project.Data) up with some DI framework like Castle Windsor.

Project.UI.Web follows the following conventions:

• its models are only(!) viewmodels
• the views consume their own viewmodel (one-view-one-viewmodel)
• the controllers just need to validate the input, transforms it into domain objects (as the business logic knows exacly nothing about viewmodels) and delegate the real work (business logic) to the business services.

Summary:
If you follow this model it's helpful to focus on Project.Core: that is the real application. It doesn't worry about the real persistence of data nor cares about how does it get presented. It's just about "how-to-do-it". But it's laying out the rules and contracts (interfaces) the other projects must provide implementations for.

I hope this helps you with how to layout an Asp.Net MVC application!

Lg
warappa