Chapter 7. Routing

Routing is one of the important concepts in the ASP.NET MVC application as it takes care of incoming requests and maps them to the appropriate controller's actions.

In this chapter, we are going to learn about the following topics:

  • Using the MapRoute method to configure routing
  • Different types of routing with examples—convention and attribute-based
  • Using HTTP verbs in attribute-based routing

We briefly discussed routing in Chapter 3 , Controllers. In this chapter, we are going to discuss routing along with several options available to customize it in ASP.NET Core.

Convention-based routing

The routing engine is responsible for mapping the incoming requests to the appropriate action method of the controller.

In the Configure method of the Startup class, we have mapped the following route:

app.UseMvc(routes => 
    { 
        routes.MapRoute(name: "default", 
        template: "{controller=Employee}/{action=Index}/{id?}"); 
    });

The MapRoute method has two parameters:

  • name: This represents the name of the route as we could configure multiple routes for the same application.
  • template: This signifies the actual configuration for the route. There are three parts to this configuration value. As we are supplying default parameters, if the values are not passed, it will take the default parameter values.
  • {controller=Employee}: The first value acts as the name of the controller and we use the Employee controller as the default controller when the controller value is not available in the URL.
  • {action=Index}: The Index action method will be acting as the default action method and the second parameter from the URL will be taken as the action method name.
  • {id?}: By specifying "?" after the id parameter, we are saying that id is the optional parameter. If the value is passed as the third parameter, the id value will be taken. Otherwise, it would not be considered.

There is another method with the same functionality. The app.UseMvcWithDefaultRoute() method configures the route "{controller=Employee}/{action=Index}/{id?}". But we have used the earlier method to show that we can customize the route as we want.

Let us see a few examples and observe how our routing engine works. We are assuming the following routing for the preceding examples:

"{controller=Employee}/{action=Index}/{id?}"

Example 1

URL-http://localhost:49831/

In this URL, we have not passed a value for the controller, action, or id. Since we have not passed anything, it would take the default values for the controller and the action. So, the URL is converted into the following URL by the routing engine:

http://localhost:49831/Employee/Index

Example 2

URL-http://localhost:49831/Employee/

In this URL, we have passed the value for the controller (the first parameter), which is Employee, whereas we did not pass anything for action method (the second parameter) or id (the third parameter). So, the URL will be converted into the following URL by taking the default value for the action method:

http://localhost:49831/Employee/Index

Example 3

URL-http://localhost:49831/Manager/List

The routing engine will take the first parameter, Manager, as the controller method name and the second parameter, List, as the action method name.

Example 4

URL-http://localhost:49831/Manager/Details/2

We have passed all three parameters in this URL. So, the first parameter value, Manager, will be considered as the controller method name, the second parameter value will be considered as the action method name, and the third parameter value will be considered as the id method name.

When defining the map route, we have used the MapRoute method with a couple of parameters. The first parameter, name, represents the name of the route and the second parameter, template, represents the URL pattern to be matched along with the default values:

routes.MapRoute(name: "default",
               template: "{controller=Employee}/{action=Index}/{id?}");

There are other overloaded variations of this MapRoute method. The following is another commonly overloaded MapRoute method, where the incoming URL pattern and the default values are passed for different parameters. The name of the route is FirstRoute and this route will be applied for all URLs starting with Home. The default values for the controller and the action are Home and Index2 respectively:

routes.MapRoute(name:"FirstRoute",
               template:"Home",
               defaults:new {controller ="Home", action="Index2"});

You can define any number of routing maps for your ASP.NET MVC application. There is no restriction or limit on the routing maps. Let us add another routing map to our application. We have added another route map called FirstRoute to our application (highlighted in bold):

public void Configure(IApplicationBuilder app) 
    { 
        app.UseIISPlatformHandler(); 
        app.UseMvc(routes => 
        { 
            routes.MapRoute(name:"FirstRoute",
            template:"Home", defaults:new {controller ="Home", action="Index2"});

            routes.MapRoute(name: "default",
            template: "{controller=Employee}/{action=Index}/{id?}");
        }); 
    }

And we have added another controller method by the name HomeController with a couple of simple action methods returning different strings:

public class HomeController : Controller 
    { 
        // GET: /<controller>/ 
        public IActionResult Index() 
        { 
            return Content("Index action method"); 
        } 
 
        public IActionResult Index2() 
        { 
            return Content("Index2 action method"); 
        } 
    }

When you try to access the application through the URL, http://localhost:49831/Hello, both routing maps, FirstRoute and the default, match with the URL pattern.

Which map routing, do you think, will get applied in this scenario?

The routing engine maps the incoming URL based on the following factors:

  1. Matching pattern.
  2. On the order defined in the routing engine.

The first factor is an obvious one. For a routing map to be picked up by the routing engine, the pattern of the incoming URL should get matched with the defined template in the routing map.

The second factor is subtle but important. If more than one routing map matches with the incoming URL, the routing engine will pick the first URL as defined in the configuration. For example, if the incoming URL matches with both the FirstRoute and default maps, the routing engine will pick the FirstRoute map as it was defined first in the configuration.

Example 4

If the routing engine could not map the incoming URL to any of the mapping routes, we get an HTTP 404 error, meaning that no resource could be found. You can see the status (200 means OK, 404 means No resource found) by looking at the Network tab in the developer tools as shown in the following screenshot:

Example 4

..................Content has been hidden....................

You can't read the all page of ebook, please click here login for view all page.
Reset