The routing engine is responsible for getting the incoming request and routing that request to the appropriate Controller based on the URL pattern. We can configure the routing engine so that it can choose the appropriate controller based on the relevant information.

By convention, ASP.NET MVC follows this pattern: Controller/Action/Id.

If the user types the URL http://yourwebsite.com/Hello/Greeting/1, the routing engine selects the Hello controller class and Greeting action method within the HelloController, and passes the Id value as 1. You can give default values to some of the parameters and make some of the parameters optional.

The following is the sample configuration:

The template: "{controller=Hello}/{action=Greeting}/{id?}");

In the preceding configuration, we are giving three instructions to the routing engine:

Let us discuss how the routing engine selects the controller classes, action methods, and Id values for different URLs:

URL1:http://localhost/ 
Controller: Hello 
Action method: Greeting 
Id: no value is passed for the id parameter 

Reasoning: The Hello controller is passed as the default value as per the routing configuration, as no value is passed as the Controller in the URL.

The following action method will be picked up by the routing handler when the preceding URL is passed:

public class HelloController : Controller { 
  public ActionResult Greeting(int id) { 
    return View(); 
  } 
}
 
URL2: http://localhost/Hello/Greeting2 
Controller: Hello 
Action method: Greeting2 
Id: no value is passed for the id parameter 

Reasoning: The Hello controller will be chosen as the URL contains Hello as the first parameter, and the Greeting2 action method will be chosen as the URL contains Greeting2 as the second parameter. Please note that the default value mentioned in the configuration would be picked only when no value is present in the URL. As the id parameter is optional and the URL does not contain the value for id, no value is passed to the id parameter.

The following action method Greeting2 will be picked up by the routing handler when the preceding URL is passed:

public class HelloController : Controller { 
  public ActionResult Greeting(int id) { 
    return View(); 
  } 
 
  public ActionResult Greeting2(int id) { 
    return View(); 
  } 
} 
 
URL3: http://localhost/Hello2/Greeting2 
Controller: Hello2 
Action method: Greeting2 
Id: no value is passed for the id parameter 

Reasoning: As Hello2 is passed as the first parameter, the Hello2 controller will be selected, and Greeting2 is the action method selected since Greeting2 is passed as the second parameter. As the id parameter is optional and no value is passed for the parameter id, no value will be passed for the id.

The following action method will be picked up by the routing handler when the preceding URL is passed:

public class Hello2Controller : Controller { 
  public ActionResult Greeting2(int id) { 
    return View(); 
  } 
} 
URL4: http://localhost/Hello3/Greeting2/1 
Controller: Hello3 
Action method: Greeting2 
Id: 1 

Reasoning: Hello3 is the controller selected as it is mentioned as the first parameter, Greeting4 is the action method, and 1 is the value passed as the id.

The following action method will be picked up the routing handler when the preceding URL is passed:

public class Hello3Controller : Controller { 
  public ActionResult Greeting2(int id) { 
    return View(); 
  } 
} 

We will discuss routing in detail in a later chapter.

Once the request reaches the controller, the controller will create a response by talking to the Model and may pass the data to View and the View will then be rendered to the end user.