MVC http request flow

This is a good diagram that shows how a http request flow work in the MVC framwork.

Request Flow

In regular ASP.NET web form applications, URLs are usually mapped to physical disk files. When a URL is requested, the code of the associated file gets executed, which generates the HTML. However, in the ASP.NET MVC Framework the URLs are tied with the Controllers rather than the disk file. The component that is responsible to map the URL with the Controller is the Routing Handler. When the application starts, it is required to register the URL Routing Rules, which the Routing Handler uses to map the controller when the request arrives. Let's take a quick view of how a request is carried in different layers of the ASP.NET MVC Framework:

Figure 2: The Request Flow

• The user requests a URL.
• The ASP.NET MVC Framework evaluates the requested URL against the registered Routing Rules and finds a matching Controller. The Framework forwards the request to the matching Controller.
• The Controller calls the Model to build ViewData. It can call the model multiple times depending upon the ViewData that it is building.
• The Model, as mentioned earlier, is the middle tier, which might involve data access components, workflow activities, external web service dependencies etc. The Model returns the requested data to Controller.
• The Controller selects a View and passes the data to the View which it previously got from the Model. The View Renders the data and returns the generated HTML to the User.