Routing in a .NET Core API is the process of mapping HTTP requests to action methods in controllers. It is used to define how users can access your API.

There are two ways to define routing in a .NET Core API:

• Attribute routing: Attribute routing is the most common way to define routing in a .NET Core API. It uses attributes to map HTTP requests to action methods.
• Conventional routing: Conventional routing is a less common way to define routing in a .NET Core API. It uses conventions to map HTTP requests to action methods.

Here is an example of attribute routing in a .NET Core API:

C#

[ApiController]
[RoutePrefix("/products")]
public class ProductController : ControllerBase {

  [HttpGet]
  public IActionResult GetProducts() {
    // ...
  }

  [HttpPost]
  public IActionResult CreateProduct(Product product) {
    // ...
  }
}

In this example, the GetProducts() action method is mapped to the /products endpoint because it has the HttpGet attribute. The CreateProduct() action method is mapped to the /products endpoint because it has the HttpPost attribute.

Here is an example of conventional routing in a .NET Core API:

C#

[ApiController]
public class ProductController : ControllerBase {

  [Route("products")]
  public IActionResult GetProducts() {
    // ...
  }

  [Route("products", HttpMethod.Post)]
  public IActionResult CreateProduct(Product product) {
    // ...
  }
}

In this example, the GetProducts() action method is mapped to the /products endpoint because its method name matches the route name. The CreateProduct() action method is mapped to the /products endpoint because its method name matches the route name and the HTTP verb is POST.

Here are some additional tips for defining routing in a .NET Core API:

• Use attribute routing whenever possible. It is more flexible and easier to maintain than conventional routing.
• Use meaningful route names. This will help users to understand how to access your API.
• Use the RoutePrefix attribute to group related routes together. This will help to keep your URLs organized and easy to understand.
• Use the ApiVersion attribute to specify the API version for each route. This will help to ensure that your API is backward compatible.