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

Attribute routing allows us to specify URL routes directly in controllers and actions using attributes like [Route], [HttpGet], [HttpPost].

It is a very flexible, convenient, and easy-to-maintain approach. So it is the preferred and most commonly used routing method in ASP.NET applications.

Initial setup

Before we can use attribute routing, we must first enable it in the Program.cs file.

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddControllers();

var app = builder.Build();

app.MapControllers(); // Enables attribute routing
app.Run();

Main routing attributes

We have two “families” of parameters available for use.

Let’s look at each of them,

[Route("api/products")]
public class ProductsController : ControllerBase
{
    // Here the routes start with /api/products
}

[HttpGet]
public IActionResult Get() { ... }

Complete example

Let’s see how to use each of them with a complete example, where we use them together,

[Route("api/products")]
public class ProductsController : ControllerBase
{
    [HttpGet] // GET /api/products
    public IActionResult GetAll() => Ok();

    [HttpGet("{id}")] // GET /api/products/5
    public IActionResult GetById(int id) => Ok();

    [HttpPost("create")] // POST /api/products/create
    public IActionResult Create([FromBody] Product product) => Ok();

    [HttpDelete("delete/{id}")] // DELETE /api/products/delete/5
    public IActionResult Delete(int id) => Ok();
}

Route parameters

Of course, attribute routing allows us to receive parameters, both in simple routes and complex patterns.

These parameters can be captured directly from the URL and automatically mapped to the arguments of our methods.

Basic parameters

Parameters are defined within curly braces {} and are automatically mapped to method parameters:

[HttpGet("category/{category}/product/{id}")]
public IActionResult GetProductByCategory(string category, int id)
{
    // GET api/products/category/electronics/product/123
    return Ok($"Product {id} in category {category}");
}

Advanced routing patterns

[Route("api/[controller]")]
public class OrderController : ControllerBase
{
    [HttpGet("{orderId}/items/{itemId}")]
    public IActionResult GetOrderItem(int orderId, int itemId)
    {
        // Logic to get the order item
    }
}

[HttpGet("page/{number:int=1}")]
public IActionResult GetPage(int number)
{
    // GET api/products/page -> number = 1
    // GET api/products/page/5 -> number = 5
    return Ok();
}

[HttpGet("list/{category?}")]
public IActionResult ListProducts(string category = null)
{
    // GET api/products/list
    // GET api/products/list/electronics
    return Ok();
}

[HttpGet("search/{term}")]
[HttpGet("find/{term}")]
public IActionResult SearchProducts(string term)
{
    // Accessible from both routes:
    // GET api/products/search/laptop
    // GET api/products/find/laptop
    return Ok();
}

Route constraints

Route constraints allow limiting the values that parameters can take in a route.

Some of the most common constraints include:

To apply them, we can specify types and constraints directly in the template:

[Route("api/[controller]")]
public class UserController : ControllerBase
{
    [HttpGet("{id:int}")]
    public IActionResult GetUser(int id)
    {
        // Logic to get the user
    }

    [HttpGet("{name:alpha}")]
    public IActionResult GetUserByName(string name)
    {
        // Logic to get the user by name
    }
}