Asp.net-mvc – How MVC (ASP.NET MVC) band 3-tier architecture can work together

M) M is your model. This is generally living in your business layer or the layer just behind your presentation layer. Many people don't like the presentation layer to have any knowledge of the business layer though and so they further abstract that by having what is called a ViewModel. These frequently are DTO (data transfer objects) that loosely map to your Domain model. For me (.net guy) there are tools such as AutoMapper to make the conversion from Domain Model to View Model.

V) V is your view. The view is your presentation layer. This is the actual HTML or PHP code that the user directly touches and interacts with. The view should be as light as possible (meaning no logic if possible). Try to keep any sort of if/then type scenarios out of the view and stick to just displaying and collecting data. Present a ViewModel to your web designers so that they don't contaminate your DomainModel.

C) C is your controller. This is much like a co-ordinator. It takes data from your view and makes sure it gets to the right back end function/method for processing that data. It also co-ordinates data from the back end on it's way to the front end.

Where multi-tier design concepts come in is behind the Presentation layer (where is where MVC is primarily). When the controller is taking data from the view and passing it back to the back end it (if you follow DDD or Domain Driven Design) would pass the data to an application service (a class that co-ordinates back end matters). The service might further push the data into a Repository layer (which is a class that speaks to the database, filesystem, web services, etc. - any infrastructure stuff). DDD is a big topic but will get your head around the n-tier approach and how it works with MVC.

While researching this topic take a look at IoC (inversion of control), DI (dependency injection), TDD (test driven development), and as many patterns as possible (facade, factory, etc.).

You don't use a file input control. Server side controls are not used in ASP.NET MVC. Checkout the following blog post which illustrates how to achieve this in ASP.NET MVC.

So you would start by creating an HTML form which would contain a file input:

@using (Html.BeginForm("Index", "Home", FormMethod.Post, new { enctype = "multipart/form-data" }))
{
    <input type="file" name="file" />
    <input type="submit" value="OK" />
}

and then you would have a controller to handle the upload:

public class HomeController : Controller
{
    // This action renders the form
    public ActionResult Index()
    {
        return View();
    }

    // This action handles the form POST and the upload
    [HttpPost]
    public ActionResult Index(HttpPostedFileBase file)
    {
        // Verify that the user selected a file
        if (file != null && file.ContentLength > 0) 
        {
            // extract only the filename
            var fileName = Path.GetFileName(file.FileName);
            // store the file inside ~/App_Data/uploads folder
            var path = Path.Combine(Server.MapPath("~/App_Data/uploads"), fileName);
            file.SaveAs(path);
        }
        // redirect back to the index action to show the form once again
        return RedirectToAction("Index");        
    }
}