MVC Architecture And Its Pipeline

@if (user.Role == "Admin") { }
else { }

public ActionResult Index()
{
    if (ModelState.IsValid)
    {
        dbContext.Employees.Add(model);
    }
    return RedirectToAction("Saved");
}

public ActionResult Contact()
{
    ViewBag.Message = "Your contact page.";
    return View();
}

Characteristics of MVC

These are the main characteristics of ASP.NET MVC,

• Enables clean separation of concerns (SoC).
• Follows the design of the stateless nature of the web.
• Provides Test Driven Development (TDD).
• Easy integration with JavaScript frameworks.
• Provides full control over the rendered HTML.
• No ViewState and PostBack events

Pipeline in MVC

We can say that the pipeline of MVC contains the following processes.

• Routing
• Controller Initialization
• Action Execution
• Result Execution
• View Initialization and Rendering
  

Let’s understand them one by one!

Routing

Routing is the first step in the ASP.NET MVC pipeline. In fact, it is a pattern-matching system that matches the incoming request to the registered URL patterns which reside in the Route Table.

Routing is a system in which URL patterns are matched with the URL patterns defined in the RouteTable by using the MapRoute method. The process of Routing comes into action when the application starts, firstly it registers the routes in the RouteTable. This registration of routes in the RouteTable is essential because it is the only thing that tells the Routing Engine how to treat the requested URL requests. The routes are registered in the RouteConfig class App_Start file of the application. Let's have a look at it.

public class RouteConfig
{
    public static void RegisterRoutes(RouteCollection routes)
    {
        routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
        
        routes.MapRoute(
            name: "Default",
            url: "{controller}/{action}/{id}",
            defaults: new
            {
                controller = "Home",
                action = "Index",
                id = UrlParameter.Optional
            }
        );
    }
}

The Global. asax file looks like.

protected void Application_Start()
{
    // Some other code is removed for clarity.
    RouteConfig.RegisterRoutes(RouteTable.Routes);
}

The Routing Engine is the module whose responsibility is to treat the HTTP request. When an HTTP request comes, the UrlRoutingModule starts matching the perfect URL pattern from the RouteTable, when found successfully, the Routing Engine forwards the request to RouteHandler.

In RouteHandler its interface IRouteHandler comes into action and calls its GetHttpHandler method. This method looks as below.

public interface IRouteHandler
{
    IHttpHandler GetHttpHandler(RequestContext requestContext);
}

After finding the route successfully, the ProcessRequest() method is invoked, as shown in the figure above, otherwise, user will receive an HTTP 404 error page.

Controller Initialization

While the ProcessRequest() method is invoked, it uses the IControllerFactory instance to create the controller for the URL request. The IContollerFactory is responsible to instantiate and return an appropriate controller and this created controller will become the subclass of the Controller base class.Then the Execute() method is invoked.

ProcessRequest() method looks like this.

protected internal virtual void ProcessRequest(HttpContextBase httpContext)
{
    SecurityUtil.ProcessInApplicationTrust(delegate
    {
        IController controller;
        IControllerFactory factory;
        this.ProcessRequestInit(httpContext, out controller, out factory);
        try
        {
            controller.Execute(this.RequestContext);
        }
        finally
        {
            factory.ReleaseController(controller);
        }
    });
}

Action Execution

Action Execution starts with Action Invoker. So, after the initialization of controller, it has the information about the action method, this detail of the action method is passed to the controller’s InvokeAction() method. This InvokeAction() implements the interface IActionInvoler and hence the action is selected for invoking.

public virtual bool InvokeAction(ControllerContext controllerContext, string actionName)

After ActionInvoker, Model Binders come into action. Model binders are used to retrieve the data from the HTTP request and after taking data from it, it applies the validation, and data type conversion rules on that data. For example, it checks its validity by comparing its data type with the data type of action parameters, etc. Model Binders are present in the System.Web.Mvc.DefaultModelBinder namespace.

When Model Binders take data from the requested URL then it is time to apply restrictions on the use of that data. So for this purpose, we have an Authentication filter that comes into action and authenticates the user whether that user is valid or not. You can apply authentication by using the Authenticate attribute. This authentication is done with the help of the IAuthenticationFilter interface. So you can create your own by implementing it.

After authentication after checking it the user is valid or not, the Authorization Filter comes into action and checks the user access, which means who can use the data in which way. Authorization Filter applies to the authenticated user, it doesn’t apply to unauthenticated users. So authorization filter sets the user access for the authenticated user. You can use the authorization filter by applying the Authorize attribute at the top of the action method. And this authorization is done with the help of the IAuthorizationFilter interface. So you can implement it to create your own.

After collecting data from HTTP requests, and performing authorization on any authenticated user, now is the time to execute the action. So our Action Filters come into play. Action Filters execute with the help of the IActionFilter interface. This interface has two methods that are executed before and after the action is executed, named OnActionExecuting and OnActionExecuted respectively. I’ll post another article on “How can we create a custom action filter?”

After the execution of the Action, the ActionResult is generated. Hence the process of Action Execution is completed.

Result Execution

The “Result Execution” module executes after the execution of the module “Action Execution”, in this module Result Filters come into action and execute before and after the ActionResult is executed. Result Filters are also implemented by IResultFilter, so you can create your own result filters by implementing this interface.

As you saw in the action execution section, you have Action Result as a result. There are many types of Action Results such as ViewResult, PartialViewResult, RedirectToRoute, RedirectResult, JsonResult, ContentResult, and Empty Result. These types are all categorized into two main categories named as ViewResult and Non-ViewResult types.

1. ViewResult type: ViewResult is a type of result in which the View of MVC part uses means by which an HTML page is rendered.
2. NonViewResult type: NonViewResult is a type of result that deals with only data. Data may be in text format, JSON format, or binary format.
   

View Initialization and Rendering

View Engine takes the ViewResult type and renders it as a View and shows it by using IView. The IView interface looks like as below,

public interface IView
{
    void Render(ViewContext viewContext, TextWriter writer);
}

After rendering the View, it is time to make HTML Helpers that are used to write input files, create links, forms, and much more. These helpers are extension methods of the HTML helper class. Validation rules can also be applied, for example, view should use HtmlHelpers and render a form having client-side validations.

Hence this is the pipeline of MVC. We have discussed each part very thoroughly.

Conclusion

This article included the basic and foremost things to understand about MVC architectural pattern and its pipeline. If you have any query then feel free to contact me in the comments. Also give feedback, either positive or negative, it will help me to make my articles better and increase my enthusiasm to share my knowledge.