Routing and URL Patterns

50 min

Routing is the process of mapping URLs to controllers and actions, determining which controller and action method should handle each HTTP request. ASP.NET Core's routing system examines incoming URLs and matches them to route patterns, extracting parameters and directing requests to appropriate handlers. Understanding routing is essential for building web applications. Routing enables clean, meaningful URLs that are both user-friendly and SEO-friendly.

ASP.NET Core uses a powerful routing system that can handle both conventional routing (route templates defined in configuration) and attribute-based routing (routes defined with attributes on controllers and actions). Conventional routing uses default patterns like `{controller}/{action}/{id?}`. Attribute routing uses `[Route]` attributes for fine-grained control. Understanding both approaches enables flexible routing. Attribute routing is more explicit and easier to understand.

You can define custom routes, route constraints, and route parameters to create clean, SEO-friendly URLs. Custom routes enable URLs that match your application's structure. Route constraints (like `{id:int}`) ensure parameters match expected types. Route parameters extract values from URLs. Understanding route configuration enables effective URL design. Good routing makes applications more intuitive.

Route templates define URL patterns using placeholders like `{controller}`, `{action}`, and `{id}`. Optional parameters use `?` (e.g., `{id?}`). Default values can be specified for parameters. Route constraints restrict parameter values (e.g., `{id:int}` only matches integers). Understanding route templates enables flexible routing. Route templates are powerful and expressive.

Attribute routing provides fine-grained control over routes using `[Route]`, `[HttpGet]`, `[HttpPost]`, and other HTTP method attributes. Attribute routing is more explicit than conventional routing and enables routes directly on actions. You can combine attribute routing with conventional routing. Understanding attribute routing enables precise route control. Attribute routing is preferred for APIs.

Best practices include using meaningful route names, using route constraints for type safety, keeping routes simple and intuitive, using attribute routing for APIs, and testing routes thoroughly. Understanding routing enables effective URL design. Good routing improves user experience and SEO. Routing is fundamental to web application structure.

Key Concepts

Routing maps URLs to controllers and actions.
ASP.NET Core supports conventional and attribute-based routing.
Route templates define URL patterns with placeholders.
Route constraints ensure parameters match expected types.
Attribute routing provides fine-grained route control.

Learning Objectives

Master

Understanding routing concepts and URL mapping
Configuring conventional and attribute routing
Defining custom routes with constraints
Creating clean, SEO-friendly URLs

Develop

Understanding URL design principles
Designing intuitive application URLs
Appreciating routing's role in web applications

Tips

Use attribute routing for APIs—it's more explicit.
Use route constraints to ensure type safety.
Keep routes simple and intuitive for users.
Test routes thoroughly to ensure they match correctly.

Common Pitfalls

Creating overly complex routes, making URLs confusing.
Not using route constraints, allowing invalid parameter types.
Not understanding route precedence, causing unexpected matches.
Not testing routes, causing 404 errors.

Summary

Routing maps URLs to controllers and actions.
ASP.NET Core supports conventional and attribute routing.
Route templates and constraints enable flexible URL design.
Understanding routing enables effective URL design.
Good routing improves user experience and SEO.

Exercise

Create a controller with custom routing that accepts parameters.

[Route("products")]
public class ProductController : Controller
{
    [HttpGet("{id:int}")]
    public IActionResult Details(int id)
    {
        return Content($"Product ID: {id}");
    }
    
    [HttpGet("category/{category}")]
    public IActionResult ByCategory(string category)
    {
        return Content($"Category: {category}");
    }
}

Routing and URL Patterns