What is and how to use conventional routing in ASP.NET

Conventional routing is the traditional URL mapping system in ASP.NET that uses predefined patterns to determine which controller and action should handle a specific HTTP request.

Conventional routing establishes global rules that apply to the entire application, usually in Program.cs (or Startup.cs in earlier versions).

Although minimal APIs and attribute routing are more common in modern projects, you may still encounter conventional routing in large applications or during migrations from earlier versions.

How does Conventional Routing work?

Conventional routing is based on predictable conventions that follow the standard pattern of {controller}/{action}/{id?}.

Conventional routes follow a URL pattern with this format:

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

Setting up Conventional Routing

Routing patterns are applied using methods like MapControllerRoute or MapDefaultControllerRoute.

Let’s see how conventional routing would be applied with a simple example,

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddControllersWithViews(); // Enables MVC

var app = builder.Build();

app.MapControllerRoute(
    name: "default",
    pattern: "{controller=Home}/{action=Index}/{id?}");

app.Run();

public class ProductsController : Controller
{
    public IActionResult Details(int id)
    {
        // Here would go the logic to get the product with that id
        return Content($"Displaying product with ID = {id}");
    }
}

Advanced Routing

Of course, just like with attribute routing, it is possible to create more advanced routing systems if needed for our project.

Let’s look at some of them.

app.MapControllerRoute(
    name: "blog",
    pattern: "blog/{action}/{id?}",
    defaults: new { controller = "Blog" });

app.MapControllerRoute(
    name: "blogPost",
    pattern: "blog/{year}/{month}/{day}",
    defaults: new { controller = "Blog", action = "Post" });